Applied Science, Faculty of
Engineering, School of (Okanagan)
DSpace
UBCO
Hashemi, Seyyed Alireza
Doctor of Philosophy - PhD
University of British Columbia
This thesis explores the innovative use of interfacial complexation to develop a versatile approach for manufacturing functional aerogels. The approach leverages structured liquids as engineerable templates for aerogel production, enabling precise control over the composition and features of aerogels from the nano-scale material chemistry and micro-scale nanoparticle-surfactant assemblies to the macro-scale porous architecture. This high degree of customization facilitated the creation of diverse 3D porous macroscopic constructs, including filamentous, free-standing, and 3D-printed aerogels. Such versatility addresses key challenges in porous construct manufacturing, including enhancing mechanical properties, fine-tuning multi-scale porosities, engineering macroscopic morphologies, inducing stimuli responsiveness, and tailoring compositions for advanced functional applications. The study begins with the synthesis and characterization of essential nanomaterials, including graphene oxide (GO), magnetic graphene oxide (mGO), and cellulose nanofibers (CNF), which serve as the primary building blocks for aerogel construction. This is followed by the design and optimization of the interfacial complexation technique, which involves nanoparticle jamming at the interface of immiscible liquids (oil/water) and stabilizing the non-equilibrium shape of the resulting structured liquids as templates for aerogel production. This approach led to the creation of ultra-lightweight, flexible, and multi-scale porous filamentous aerogels with customizable compositions, where GO played a critical role in maintaining the structured liquid integrity. Controlling aerogel features during the liquid structuring stage enabled the production of a wide range of functional aerogels, with a specific focus on electromagnetic (EM) shielding applications. The concept of "aerogel electromagnetic traps" was then introduced, yielding filamentous aerogels capable of capturing and dissipating incident EM waves as well as those reflected from highly conductive metallic substrates, effectively addressing key challenges in EM shielding science. Finally, an interfacially driven oil-in-water (O/W) emulsion templating method was developed, enabling scalable manufacturing of free-standing or 3D-printed aerogels with tunable mechanical properties and EMI shielding performance. This technique utilized post-jamming ionic crosslinking to modify the rheological properties of the emulsion ink, facilitating 3D printing via direct ink writing (DIW) and enabling the creation of complex macroscopic geometries. This work pushes the boundaries of functional aerogels, advancing their design and application potential for cutting-edge technological challenges.
From Interfacially Complexed Structured Liquids to Electromagnetic Shielding Aerogels By Seyyed Alireza Hashemi A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE COLLEGE OF GRADUATE STUDIES (Mechanical Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan) May 2025 © Seyyed Alireza Hashemi, 2025 ii The following individuals certify that they have read, and recommend to the College of Graduate Studies for acceptance, a thesis/dissertation entitled: From Interfacially Complexed Structured Liquids to Electromagnetic Shielding Aerogels Submitted by Seyyed Alireza Hashemi in partial fulfillment of the requirements of the degree of Doctor of Philosophy Examining Committee: Dr. Mohammad Arjmand, School of Engineering Supervisor Prof. Abbas Milani, School of Engineering Supervisory Committee Member Dr. Sina Kheirkhah, School of Engineering Supervisory Committee Member Dr. Christopher Collier, School of Engineering University Examiner Dr. Amir Ameli, University of Massachusetts Lowell External Examiner iii Abstract This thesis explores the innovative use of interfacial complexation to develop a versatile approach for manufacturing functional aerogels. The approach leverages structured liquids as engineerable templates for aerogel production, enabling precise control over the composition and features of aerogels from the nano-scale material chemistry and micro-scale nanoparticle-surfactant assemblies to the macro-scale porous architecture. This high degree of customization facilitated the creation of diverse 3D porous macroscopic constructs, including filamentous, free-standing, and 3D-printed aerogels. Such versatility addresses key challenges in porous construct manufacturing, including enhancing mechanical properties, fine-tuning multi-scale porosities, engineering macroscopic morphologies, inducing stimuli responsiveness, and tailoring compositions for advanced functional applications. The study begins with the synthesis and characterization of essential nanomaterials, including graphene oxide (GO), magnetic graphene oxide (mGO), and cellulose nanofibers (CNF), which serve as the primary building blocks for aerogel construction. This is followed by the design and optimization of the interfacial complexation technique, which involves nanoparticle jamming at the interface of immiscible liquids (oil/water) and stabilizing the non-equilibrium shape of the resulting structured liquids as templates for aerogel production. This approach led to the creation of ultra-lightweight, flexible, and multi-scale porous filamentous aerogels with customizable compositions, where GO played a critical role in maintaining the structured liquid integrity. Controlling aerogel features during the liquid structuring stage enabled the production of a wide range of functional aerogels, with a specific focus on electromagnetic (EM) shielding applications. iv The concept of "aerogel electromagnetic traps" was then introduced, yielding filamentous aerogels capable of capturing and dissipating incident EM waves as well as those reflected from highly conductive metallic substrates, effectively addressing key challenges in EM shielding science. Finally, an interfacially driven oil-in-water (O/W) emulsion templating method was developed, enabling scalable manufacturing of free-standing or 3D-printed aerogels with tunable mechanical properties and EMI shielding performance. This technique utilized post-jamming ionic crosslinking to modify the rheological properties of the emulsion ink, facilitating 3D printing via direct ink writing (DIW) and enabling the creation of complex macroscopic geometries. This work pushes the boundaries of functional aerogels, advancing their design and application potential for cutting-edge technological challenges. v Lay Summary This research focuses on creating a groundbreaking manufacturing method to produce aerogels, known as one of the lightest materials ever made by man. Imagine a Jello-like structure where the liquid is replaced with air, but the structure stays intact, that’s aerogel! What’s exciting is that these aerogels can be shaped like spaghetti, pancakes, or even intricate 3D-printed forms. We can tailor their properties to meet specific needs, unlocking endless possibilities to tackle global challenges, from absorbing and dissipating electromagnetic waves to monitoring human motion and cleaning up oil spills with a recoverable approach. Aerogels prove to be a versatile technological solution for a wide range of societal demands. vi Preface Seyyed Alireza Hashemi authored this doctoral dissertation as the outcome of his research efforts during his PhD program under the supervision of Dr. Mohammad Arjmand at the School of Engineering, University of British Columbia. Portions of this dissertation have been published as journal articles, with a summary of these publications and the author's specific contributions provided in subsequent sections. AI tools have been employed exclusively to partially refine the language and grammar to ensure the text is accurate and error-free. Importantly, these tools have been used solely for linguistic enhancement and not for generating scientific content or ideas. All research findings, data, and conclusions presented in this dissertation are the result of Seyyed Alireza Hashemi’s original experimental work. Additionally, permissions have been secured for all images used in the background and literature review sections (Chapter 2), with proper citations included in image captions where applicable. Original graphic illustrations are explicitly identified as the author's work. Journal Publications: A version of Chapter 2 has been published in the following papers: ❖ Hashemi, S. A.; Ghaffarkhah, A.; Hosseini, E.; Bahrani, S.; Najmi, P.; Omidifar, N.; Mousavi, S. M.; Amini, M.; Ghaedi, M.; Ramakrishna, S.; Arjmand, M., Recent progress on hybrid fibrous electromagnetic shields: Key protectors of living species against electromagnetic radiation. Matter 2022, 5 (11), 3807-3868. vii Contribution: I contributed to the topic ideation by considering the gap in the field, team-up, literature review, writing-reviewing-editing, graphic and structural design, obtaining permissions, finalization, and proof checking. ❖ Ghaffarkhah, A.; Hashemi, S. A.; Isari, A. A.; Panahi-Sarmad, M.; Jiang, F.; Russell, T. P.; Rojas, O. J.; Arjmand, M., Chemistry, applications, and future prospects of structured liquids. Chemical Society Reviews 2024 53, 9652-9717. Contribution: I contributed to the topic ideation, literature review, writing-reviewing-editing, graphic and structural design, and finalization. ❖ Hashemi, S.A.; Ghaffarkhah A.; Isari A.A.; Panahi-Sarmad M.; Jiang F.; Rojas O.J.; Wuttke S.; Dinca M.; Arjmand M.; Advancing from MOFs and COFs to functional macroscopic porous constructs, Advanced Materials 2024 (Revision Requested by Journal, Submitted on 07 August 2024 with Manuscript Number adma.202411617) Contribution: I contributed to the topic ideation by considering the gap in the field, team-up, literature review, writing-reviewing-editing, graphic and structural design, obtaining permissions, finalization, and proof checking. A version of Chapters 3, 4, and 5 has been published in the following paper: ❖ Hashemi, S. A.; Ghaffarkhah, A.; Goodarzi, M.; Nazemi, A.; Banvillet, G.; Milani, A. S.; Soroush, M.; Rojas, O. J.; Ramakrishna, S.; Wuttke, S.; Russell, T. P.; Kamkar, M.; Arjmand, M., Liquid‐templating aerogels. Advanced Materials 2023, 35 (42), 2302826. Contribution: I contributed to the topic ideation, experimental design, team-up, literature review, nanomaterials synthesis, aerogel or porous constructs manufacturing, viii characterization and data collection, application part completion, writing-reviewing-editing, graphic and structural design, finalization, and proof checking. A version of Chapters 3 and 6 has been published in the following paper: ❖ Hashemi, S. A.; Ghaffarkhah, A.; Ahmadijokani, F.; Yousefian, H.; Mhatre, S. E.; Sinelshchikova, A.; Banvillet, G.; Kamkar, M.; Rojas, O. J.; Wuttke, S.; Arjmand, M., Liquid-templated graphene aerogel electromagnetic traps. Nanoscale 2024, 16 (18), 8858-8867. Contribution: I contributed to the topic ideation, experimental design, team-up, literature review, nanomaterials synthesis, aerogel or porous constructs manufacturing, characterization and data collection, application part completion, writing-reviewing-editing, graphic and structural design, finalization, and proof checking. A version of Chapters 3 and 7 has been published in the following paper: ❖ Hashemi, S. A.; Ghaffarkhah, A.; Hosseini, H.; Arjmand, M., 3D-printed interfacially jammed emulsion aerogels. ACS Applied Materials & Interfaces 2024, 16 (35), 46923–46936. Contribution: I contributed to the topic ideation, experimental design, team-up, literature review, nanomaterials synthesis, aerogel or porous constructs manufacturing, characterization and data collection, application part completion, writing-reviewing-editing, graphic and structural design, finalization, and proof checking. ix Conference Publications and Presentations: ❖ Hashemi S.A.; Ghafarkhah A.; Kamkar M.; Arjmand M., Mechanically robust 3D liquid-liquid printed graphene-based aerogels toward effective electromagnetic shielding and thermal insulation, Canadian Chemical Engineering Conference. October 23-26, 2022, Vancouver, Canada. ❖ Hashemi S.A.; Ghafarkhah A.; Arjmand M., Anti-reflection interfacially complexed graphene-cellulose aerogels, BPI Research Day Poster Competition. May 4, 2024, Vancouver, Canada. x Table of Contents Abstract………………………………………………………………………………………..…iii Lay Summary……………………………………………………………………………….…….v Preface………………………………………………….…………………………..……….……vi Table of Contents….………………………………………….………………………..….…....…x List of Tables….………………………………………….……………………....……..………xiii List of Figures….………………………………………….…………………….....……………xiv List of Symbols….………………………………………….………………………...………xxviii List of Abbreviations….………………………………………….………………………..……xxx Acknowledgment….………………………………………….……………………...…….…xxxiii Dedication…………………………………………………………………………………….xxxiv Chapter 1: Thesis Organization & Key Argument….…………………………………………1 1.1.Thesis motivation….………………………………………….…………………….…………1 1.2. Research gap and objectives….………………………………………….…………...………3 1.3. Hypothesis, tasks, and outcomes………………………………………………………..…….7 1.4. Thesis organization & scientific progress….………………………………………...………11 Chapter 2: Background & Literature Review….……………………………………..………15 2.1. Structured liquids: Solid-like interfacial assemblies….……………………………….….…15 2.1.1. Nanoparticle surfactants: From discovery to direct evidence….………………………17 2.1.2. From nanoparticle surfactants to macroscale structured liquids…………………….…21 2.1.2.1. Structured Pickering emulsions and emulgels……………………………….……21 2.1.2.2. All-liquid molding…………………………………………………………...……26 2.1.2.3. Liquid streaming and 3D liquid-in-liquid printing…………………….….………28 2.1.2.4. Bicontinuous interfacially jammed emulsion gels (Bijels) ………………………31 2.2. EMI shielding fundamentals and mechanism………………………………………….……35 2.2.1. EMI shielding measurements and scattering parameters………………………………38 2.2.2. Shielding effectiveness…………………………………………………………………39 2.2.3. Evaluating the dominant shielding mechanism: basic concepts and a common mistake..42 2.2.4. EMI shielding mechanisms of fibrous and porous materials………………….……..…43 xi 2.3. Aerogel fabrication protocols……………………………………………………………..…45 2.3.1. Liquid-templated soft materials and aerogels…………………………………….……49 2.3.2. Conductive liquid-templated aerogels for EMI shielding……………………..…….…51 Chapter 3: Nanomaterials Synthesis & Characterization……………………………..….…54 3.1. Materials…………………………………………………………………………...……..…54 3.2. Nanomaterials Synthesis………………………………………………………………….…55 3.2.1. Graphene oxide…………………………………………………………………...……55 3.2.2. Magnetic graphene oxide………………………………………………………………56 3.2.3. Cellulose nanofibers……………………………………………………………………56 3.3. Characterizations……………………………………………………………………………58 3.4. Nanomaterials Characterizations……………………………………………………………58 3.4.1. Graphene oxide…………………………………………………………………...……58 3.4.2. Magnetic graphene oxide………………………………………………………………61 3.4.3. Cellulose nanofibers……………………………………………………………………64 Chapter 4: From Structured Liquid Templates to Filamentous Aerogels……………..……66 4.1. Introduction…………………………………………………………………………….……66 4.2. Materials………………………………………………………………………………….…69 4.3. Nanomaterials synthesis…………………………………………………………….….……69 4.4. Aerogels manufacturing protocol……………………………………………………………69 4.5. Characterization………………………………………………….…………………….....…72 4.6. Results and discussion…………………………………………………………….…………73 4.7. Conclusions…………………………………………………………..…...……….….……103 Chapter 5: Functional Filamentous Aerogels……………………….……….………………104 5.1. Experimental section…………………………………………………………….…………105 5.1.1. Materials………………………………………………………………………………105 5.1.2. Methods………………………………………………………………….……………105 5.1.2.1. Aerogel manufacturing………………………………………………...…………105 5.1.2.2. Electromagnetic interference shielding assessment…………………..….………105 5.1.2.3. Oil absorption……………………………………………………………………108 5.1.3. Characterization………………………………………………………….……………109 5.2. Design and manufacturing of functional aerogels…………………………….……………109 5.2.1. Engineerable electromagnetic shielding systems……………………...………………109 5.2.2. Oil absorption capacity of filamentous aerogels………………………….……………116 xii 5.2.3. Filamentous aerogels piezoresistive capability………………………………..………123 5.2.4. Filamentous aerogels thermal insulation and Joule-heating capability…………..……125 5.3. Conclusions………………………………………………………………………...………130 Chapter 6: Aerogel Electromagnetic Traps……………………………………………..……131 6.1. Introduction…………………………………………………….………………..…………132 6.2. Materials and Methods……………………………………………………….….…………135 6.2.1. Materials………………………………………………………………………………135 6.2.2. Methods…………………………………………………………….…………………135 6.2.2.1. Nanomaterials synthesis…………………………………………………………135 6.2.2.2. Aerogel production………………………………………………………………136 6.3. Characterization……………………………………………………………………………137 6.3.1. Electromagnetic shielding measurements………………………….……….…………137 6.4. Results and Discussion……………………………………………………….…….………137 6.5. Conclusions…………………………………………………………..……………….……160 Chapter 7: From Jammed Emulsion Gels to 3D Printable Engineerable Aerogels….……162 7.1. Introduction…………………………………………………………………..…….………162 7.2. Materials and Methods…………………………………………………..…………………165 7.2.1. Materials………………………………………………………………………………165 7.2.2. Methods………………………………………………………………….……………166 7.2.2.1. Nanomaterials synthesis…………………………………………………………166 7.2.2.2. Emulsion gels and free-standing aerogels manufacturing………….……………166 7.2.2.3. 3D-printing of jammed emulsion gels……………………….……..……………167 7.2.2.4. Aerogels reduction………………………………………………….……………167 7.3. Characterization……………………………………………………..…………..…………167 7.4. Conductivity and electromagnetic shielding assessment……………….……….…………168 7.5. Rheology assessment………………………………………………………………………168 7.6. Results and discussion……………………………………………………..………………169 7.7. Conclusions………………………………………...………………………………………211 Chapter 8: Conclusions & Future Prospects…………………………………...……………213 8.1. Summary of main findings…………………………………………………………………213 8.2. Technical challenges……………………………………………………………….………222 8.3. Future works recommendation………………………………………………….…………224 Bibliography……………………………………………………………………………………227 xiii List of Tables Table 2.1. Recently developed nanoparticle surfactant (NPS) systems and the resulting liquid construct with a solid-like behavior………………………………………………………………19 Table 4.1. Composition and processing conditions of each aquatic ink………………...……….72 Table 4.2. Mechanical performance of liquid templated aerogels compared with recent practices in the field by considering the density of aerogels………………………………….……………98 Table 5.1. A view of specific shielding effectiveness of developed engineerable aerogels compared with previous studies……………………………………………………………...…………….114 Table 5.2. Electromagnetic shielding performance of reduced engineerable aerogels compared with the recent practices in the literature………………………………………………………..114 Table 5.3. Oil/organic solvent absorption of the double reduced GO aerogel compared with previous practices in the literature………………………………………………………………119 Table 6.1. EMI shielding performance of the rGO-CNF aerogel with large and small filaments compared to recently developed porous constructs…………………………………….……….153 Table 6.2. Shielding parameters and coefficients of metallic substrates; the recorded parameters are average of four assessments in the whole X-band frequency range (8.2-12.4 GHz)….…….157 Table 6.3. Shielding parameters and coefficients of hybrid aerogel (6 mm thick rGO-CNF (1 wt%))-metallic substrates shielding system; the recorded parameters are average of four assessments in the whole X-band frequency range (8.2-12.4 GHz)…………………………….158 Table 6.4. The developed hybrid aerogel-metallic substrate shields compared with the recently developed shielding systems……………………………………………………………………159 Table 7.1. Prepared free-standing aerogels’ composition and tags…………………….……….167 Table 7.2. Extracted information from the X-ray diffractions of non-reduced aerogels….…….179 Table 7.3. Extracted information from the X-ray diffractions of reduced aerogels (800 °C under Ar for 1 h)……………………………………………………………………………….………181 Table 7.4. Extracted data from the micro-Raman spectroscopy of lyophilized aerogels before and after thermal annealing………………………………………………………………………….183 Table 7.5. The mechanical performance and density of the free-standing reduced/non-reduced aerogels holding different concentrations of CNC compared with the recent practices in the field……………………………………………………………………………………..………191 Table 7.6. The Shielding performance of the thermally annealed free-standing and 3D-printed aerogels…………………………………………………………………………………………211 xiv List of Figures Figure 1.1. Key parameters for manufacturing potent EM shielding aerogels…………..……….4 Figure 1.2. The schematic presentation showcases the main aim of this thesis to develop an aerogel manufacturing roadmap, enabling engineerable 3D-structured aerogels with control over their payload, porosity across dimensions, composition, mechanical properties, task-oriented functions, and EMI shielding mechanism………………………….…………………………………..……..7 Figure 1.3. The planned roadmap of this thesis………………………………………….……….14 Figure 2.1. (a) Formation of Pickering emulsion gel through the electrostatic interaction between the carboxylic acid functionalized nanoparticles in the aqueous phase and the α,ω-diamino functionalized polymer as the colloidal surfactant in the oil phase; the displayed confocal microscopy image showcases the formation of Pickering emulsion gel in which the oil phase is stained with Nile Red. (b) Interfacial complexation and formation of Pickering emulsion gel through the electrostatic interaction between the negatively and positively charged nanoparticles and polymeric surfactant at the oil/water interface, starting from tailing and intra-droplet looping to inter-droplet bridging and looping. (a-b) Reproduced with permission.6 Copyright 2018, Wiley-VCH……………….……………….……………….……………….……………………..…….22 Figure 2.2. (a) From the formation of Pickering emulsion gel to 3D printing; step 1) emulsification of the aqueous phase containing nanoparticles and the oil phase containing ligand via homogenizer leading to Pickering emulsion gel formation; the jammed emulsion system provides the possibility to tune the viscoelastic character of the ink toward direct ink writing. Step 2) 3D printing of the jammed emulsion gel, controlling the spatial arrangement of 3D constructs. Step 3) crosslinking and reduction, and step 4) drying to yield a 3D structured construct with the ability to add water soluble and non-soluble nanoparticles in each water and oil phase, respectively. (a) Reproduced with permission.31 Copyright 2021, Nature Publishing Group. (b) Formation of emulsion gel through interfacial complexation of MXene/GO and octadecyl amine as the ligand, enabling direct ink writing and 3D structural design. The jamming process allows tuning the rheological and viscoelastic characteristics of the ink toward 3D printing. (b) Reproduced with permission.3 Copyright 2022, American Chemical Society……………….……………….…………………..25 Figure 2.3. (a) The process of all-liquid molding, starting from (I) prewetting the mold with oil/ligand solution and placement of the CNC suspension in the mold. (II) Immersion of the mold into the oil/ligand solution and (III) its subsequent density-driven extraction from the mold. (b) Surface coverage of the CNCSs assemblies altered via the variation of pH. (c) Effect of pH on the shape fidelity of the molded liquid constructs, and (d) formation of molded liquid structured alphabets via the liquid molding strategy. (a-d) Reproduced with permission.8 Copyright 2018, Wiley-VCH……………….……………….……………….……………….……………..……..28 Figure 2.4. (a) Liquid-in-liquid printing of aqueous phases containing carboxylated nanoparticles into highly viscous silicon oil. This method generates liquid constructs with a pre-defined 3D xv architecture upon NPS formation and creation of an elastic film at the interface. (a) Reproduced with permission.26 Copyright 2018, Wiley-VCH. (b) Schematic illustration of an all-fluidic device fabricated through interfacial complexation of nanoclay and polymeric surfactant, holding the integrity of the liquid constructs and allowing the flow of fluids through the channels. (c) The disconnection of microchannels in all-liquid microfluidic devices is possible by simply cutting the bridged connections. (b-c) Reproduced with permission.27 Copyright 2019, Nature Publishing Group. (d) Liquid-in-liquid printed constructs with tunable electrical conductivity, mechanical robustness, and morphology; the 3D printed threads form upon extruding the PEDOT:PSS-based aqueous suspensions into an oil phase enriched with amine-functionalized PDMS. (e) Schematic illustration of PSS-stabilized hydrogel threads within ligand-enriched silicone oil after UV curing of the acrylate monomer. (d-e) Reproduced with permission.28 Copyright 2023, Nature Publishing Group……………….……………….……………….……………….…………………...……..31 Figure 2.5. (a) Schematic illustration of ternary phase diagram showcasing diverse emulsion states. (a) Reproduced with permission.50 Copyright 2021, Elsevier. (b) Ternary phase diagram showing the formation of oil in water (O/W), water in oil (W/O), or bicontinuous emulsion upon changing the concentration of oil, water, and surfactant with respect to each other. (b) Reproduced with permission.52 Copyright 2021, American Chemical Society……………….……………….34 Figure 2.6. Bijel formation via NPS assemblies; (a) schematic illustration of Bijel formation by NPSs jamming at the oil/water interface. (b) Stabilized emulsion system based on PDMS-NH2 dissolved in toluene with molecular weights of (i) 1000 g mol-1 and (ii) 3000 g mol-1 plus an aqueous phase containing 1 mg ml-1 carboxylated nanoparticles. (iii) Bicontinuous arrangement of toluene/water system arrested via NPS assemblies with equimolar PDMS-NH2 with a molecular weight of 1000 and 3000 g mol-1 at nanoparticle concentration of 0.5 mg ml-1. (c) Formed NPS assemblies with nanoparticle concentrations of (i) 0.1 and (ii) 0.5 mg ml-1 at a fixed PDMS-NH2 concentration. Arrangement of the bicontinuous network at a fixed nanoparticle concentration of 1 mg ml-1 and variable PDMS-NH2 concentrations of (iii) 0.161 and (iv) 16.1 mmol L-1. As can be seen, a change in the nanoparticle or ligand concentration can significantly affect Bijel’s arrangement. (a-c) Reproduced with permission.9 Copyright 2017, Nature Publishing Group……………….……………….……………….……………….…………………...……..35 Figure 2.7. The interaction mechanisms between EM waves and diverse structures including (a) laminated thin-film, (b) layer-by-layer stacked configuration, (c) porous structure, and (d) segregated structure, (e) schematic of scattering parameters in a vector network analyzer (VNA) sample holder, (f) the relationship between R and SER in EMI shielding measurements, (g) enhanced internal scattering in various fibrous EMI shields, including electrospun fibers/mats (Reprinted with permission from ref. 79, Copyright 2021 Elsevier), (h) fibrous aerogels (Reprinted with permission from ref. 77, Copyright 2022 Elsevier), and (i) layered fibrous structures (Adopted with permission from ref. 80, Copyright 2021 Wiley VCH) ……………….……………………..45 xvi Figure 2.8. Potential supporting scaffolds to yield free-standing aerogels, including wood aerogel, carbon aerogel, chitosan-based aerogel, aramid nanofiber-based fibrous aerogels, melamine foams, polyacrylonitrile (PAN) fibrous aerogels, and cellulose aerogels……………….………………..48 Figure 2.9. Schematic showing the fabrication of MXene-based structured Pickering emulsions that were used for developing aerogel-based EMI shields through the liquid templating approach. Reproduced with permission.40 Copyright 2019, Wiley-VCH……………….…………………..53 Figure 3.1. The outcome of the characterization for exfoliated GO flakes; (a) FTIR spectrum of GO, (b) micro-Raman spectroscopy of GO, (c) X-ray diffractogram of GO, (d-f) FESEM images of well-exfoliated GO flakes, (g) HRTEM image of single atomic layer GO flake, (h) high magnification HRTEM image of GO, and (i) SEAD pattern of GO flakes………………..…….60 Figure 3.2. (a) FESEM image of the focus area for EDX assessment; the scale bar is equal to 100 µm. (b) EDX analysis of GO flakes along with the elemental distribution in wt%, (c) EDX mapping analysis of GO flakes…………………………………………………………………………….61 Figure 3.3. (a) X-ray diffractogram, (b) micro Raman spectroscopy, and (c & d) FESEM images of GO-Fe3O4 flakes; the scale bar corresponds to 20 µm………………………………….…….63 Figure 3.4. (a) FESEM image of the focus area for EDX assessment; the scale bar is equal to 10 µm. (b) EDX analysis of GO-Fe3O4 flakes along with the elemental distribution in wt%, (c) EDX mapping analysis of GO-Fe3O4 flakes……………………………………………………..…….64 Figure 3.5. Characterization of CNF including (a) FTIR, (b) X-ray diffractogram, and (c) AFM analyses………………………………………………………………………………….……….65 Figure 4.1. Schematic illustration of the liquid templating methodology. (a) The developed process for generating hierarchical 3D aerogels with desired components and functionality, starting from injecting aqueous phase containing GO into an immiscible liquid, i.e., hexane, containing POSS-NH2 (Phase I) to freezing of liquid template (Phase II) and subsequent lyophilization to generate filamentous aerogels (Phase III). The aerogels comprise core-shell filaments with a thin solid skin wrapped around a porous core. In Phase I, * showcases the injection of aqueous GO-based inks into the hexane domain containing POSS-NH2, and ** indicates the interfacial complexation, viz., electrostatic interaction of ligands and NPs. As illustrated in Part II, the placement of the aqueous liquid template into a freezer at -85 °C leads to its freezing, whereas the hexane domain remains liquid owing to its low freezing point (-95.3 °C), enabling its separation before lyophilization. (b) Electrostatic interaction of POSS-NH2 molecule with GO through carboxylic acid deprotonation and amine functional group protonation. (c) (I) Break up of the liquid stream into discrete droplets to suppress instabilities, and (II) enhanced integrity of the liquid stream upon formation of NPSs at the interface, locking in the non-equilibrium shape of the liquid construct in the form of the filament. (d) The shape of the droplet in pendant drop tensiometry (I) in equilibrium without the presence of POSS in the oil phase and (II) in non-equilibrium shape upon the formation of a solid xvii skin around the droplet as a result NPSs jamming, holding the integrity of liquid construct; the black dots in the image represent the GO dispersed in the aqueous phase……………………….75 Figure 4.2. (a) Schematic illustration of 3D aerogels formation, showcasing (I) the freezing of the liquid template and (II) formation of aerogel after lyophilization, (b) production of aerogels with different compositions and characteristics, including (I) GO aerogel, (II) GO-Fe aerogel, and (III) GO-CNF aerogel; in this image, the brownish flakes in part (II) represent the GO-Fe3O4 flakes and the fibers on the aerogel in part (III) denote CNF. (c) Microfluidic injection of different aqueous inks, including (I) GO ink, (II & III) GO:GO-Fe3O4 ink, and (IV) GO:CNF ink into the non-polar hexane domain containing 1 mg mL-1 POSS-NH2; the concentrations of all inks were set at 10 mg mL-1. Formation of 3D liquid constructs out of (d) GO ink, (e) GO:GO-Fe3O4 ink, and (f) GO:CNF ink. Scale bars are equal to (c) (I) ~14.1 mm, (II) ~13.9 mm, (III) ~14.7 mm, and (IV) ~13.9 mm, (d) (I) ~12.3 mm, (II) ~3.8 mm, (e) (I) ~12.9, (II) ~6.8 mm, (f) (I) ~12.2 mm, and (II) ~6.1 mm. Of note, the showcased images in parts (c-f) were taken by a digital camera, and their scale bars are approximate. (g) Interfacial characteristics of different concentrations of aqueous GO suspension in non-polar hexane domain with and without POSS-NH2 (1 mg mL-1). (h) Interfacial tension of different aqueous inks containing GO, GO:CNF, and GO:GO-Fe3O4, with an initial concentration of 10 mg mL-1 in the hexane domain containing 1 mg mL-1 POSS-NH2. (i) Contraction and expansion assays of 1 mg mL-1 aqueous GO suspension within the hexane-POSS-NH2 medium; the wrinkles formed on the droplets imply the formation of elastic assemblies at the interface, i.e., interfacial complexation, as a result of NPs jamming…………………………….79 Figure 4.3. Dynamic interfacial tension of aqueous GO suspensions in hexane (a) at 1 mg mL-1 concentration without POSS-NH2, (b) at 1 mg mL-1 concentration with POSS-NH2, (c) at 10 mg mL-1 concentration without POSS-NH2, and (d) at 10 mg mL-1 concentration with POSS-NH2. As evidenced, an increase in the concentration of GO in the presence of POSS-NH2 remarkably minimized the interfacial tension, paving the way for stable liquid templating………………….80 Figure 4.4. Dynamic interfacial tension of aqueous hybrid inks containing equal weight ratio (1:1) of (a) GO:CNF, and (b) GO:GO-Fe3O4 at the fixed concentration of 10 mg mL-1 against hexane-POSS-NH2 medium………………………………………………………………………..…….80 Figure 4.5. The contraction of the pendent drop of 10 mg mL-1 aqueous GO suspension in hexane containing 1 mg mL-1 POSS-NH2…………………………………………………………….….81 Figure 4.6. The contraction of the pendent drop of 10 mg mL-1 aqueous GO:GO-Fe3O4 suspension in hexane containing 1 mg mL-1 POSS-NH2…………………………………………….……….81 Figure 4.7. The contraction of the pendent drop of 10 mg mL-1 aqueous GO:CNF suspension in hexane containing 1 mg mL-1 POSS-NH2………………………………………………….…….81 Figure 4.8. (a) Liquid templating of 5 mg mL-1 aqueous GO suspension in different solvents, including pentane, toluene, and hexane containing 1 mg mL-1 POSS-NH2; the scale bar is equal to ~15.2 mm. Formation of stable 3D-structured filamentous GO liquid templates in (b) pentane, (c) xviii toluene, and (d) hexane; scale bars are equal to (b) ~3.5 mm, (c) ~4.2 mm, and (d) ~3.7 mm. Generation of free-standing 3D-structured aerogels upon freezing and lyophilization of formed liquid templates in (e) pentane, (f) toluene, and (g) hexane; scale bars are equal to (e) ~4.8 mm, (f) ~6.9 mm, and (g) ~4.9 mm; of note, the images were acquired by digital camera and the scale bars are approximate……………………………………………………………………….…….82 Figure 4.9. (a) Non-reduced and reduced GO aerogels on the very light hairs of cactus, (b) a view of the reduced and non-reduced aerogels and a comparison of their size after the thermal annealing at 800 °C under Ar for 1 h, (c) a view of lightweight reduced GO aerogel capable of conducting the electricity to light up an LED, (d) combined electrical conductivity and magnetic response in reduced magnetic GO aerogel. FESEM images of (I) aerogels and (II) zoom in within their filaments, including (e) non-reduced GO aerogel, (f) reduced GO aerogel, (g) non-reduced GO-Fe aerogel, (h) reduced GO-Fe aerogel, (i) non-reduced GO-CNF aerogel, and (j) reduced GO-CNF aerogel. Scale bars are equal to (a) ~9.5 mm, (b) ~10.8 mm, (c) ~11.0 mm, (d) ~9.7 mm, (e-j) (I) 2 mm, and (II) 500 µm; the reported values of scale bars in parts (a) to (d) are approximate…………………………………………………………………………………..….84 Figure 4.10. FTIR spectrum of developed aerogels including (a) non-reduced GO aerogel, (b) reduced GO aerogel, (c) non-reduced GO-Fe aerogel, (d) reduced GO-Fe aerogel, (e) non-reduced GO-CNF aerogel, and (f) reduced GO-CNF aerogel…………………………………………….88 Figure 4.11. Micro-Raman spectroscopy results of (a) non-reduced GO aerogel, (b) reduced GO aerogel, (c) non-reduced GO-Fe aerogel, (d) reduced GO-Fe aerogel, (e) non-reduced GO-CNF aerogel, (f) reduced GO-CNF aerogel……………………………………………………..…….90 Figure 4.12. X-ray diffractograms of (a) non-reduced GO aerogel, (b) reduced GO aerogel, (c) non-reduced GO-Fe aerogel, (d) reduced GO-Fe aerogel, (e) non-reduced GO-CNF aerogel, (f) reduced GO-CNF aerogel………………………………………………………………….…….93 Figure 4.13. (a) Schematic illustration of the tunable internal micro-scale porosity of aerogel, including (I) GO aerogel, (II) GO-Fe aerogel, and (III) GO-CNF aerogel, via engineering the composition of manipulated NPs and subsequent treatment of the liquid template. FESEM images of tubular skin and internal micro-scale porosities of (b) (I-II) reduced GO aerogel and (c) the strain-stress curves of reduced GO aerogel at different compressive strains with six compression cycles at each respective strain rate; the inset shows the stress-strain curve of aerogels at 20% and 40% compressive strains. FESEM images of interfacially driven skin and micro-scale porosities of (d) (I-II) reduced GO-Fe aerogel and (e) (I-II) reduced GO-CNF aerogel. Scale bars are equal to (b) (I) 500 µm and (II) 200 µm, (d) (I) 200 µm and (II) 100 µm, and (e) (I-II) 50 µm. (f) Mechanical performance of the reduced GO aerogel compared with previous examples in the field. (g) The average thickness of aerogel skin in different samples. Tuning the (h) micro-scale pore size level of aerogels by changing the concentration of GO from 1 to 10 mg mL-1, and (i) manipulating the diameter of the filaments after lyophilization by changing the gauge number of the needle during ink injection or liquid templating…………………………………………………..…….97 xix Figure 4.14. (a-c) FESEM images from the core and skin of 10 mg mL-1 GO aerogels at different magnifications (I-III). For an accurate assessment, three different samples were assessed, and the thickness of the skin was analyzed using Image J software over the whole skin profile. The scale bars are equal to (a) (I) 200 µm, (II) 50 µm, (III) 20 µm, (b) (I) 100 µm, (II) 20 µm, (III) 10 µm, (c) (I) 200 µm, (II) 50 µm, (III) 5 µm…………………………………………………………….99 Figure 4.15. The thickness distribution range of GO aerogels’ skin generated via 10 mg mL-1 initial ink concentration related to (a) skin 1 (Figure 4.14 (a) III), (b) skin 2 (Figure 4.14 (b) III), and (c) skin 3 (Figure 4.14 (c) III) over the whole skin profile; the X-axis denotes the data point number with no specific order. As evidenced, the thickness of the skin is not uniform and varies within a specific range………………………………………………………………………………..….100 Figure 4.16. Change in the porosity level of GO aerogel upon changing the initial GO ink’s concentration. FESEM images showcase the porosity of aerogels formed with aqueous GO suspension with an initial concentration of (a) 1 mg mL-1, (b) 3 mg mL-1, (c) 5 m g mL-1, and (d) 10 mg mL-1 at different scale bars (I) 500 µm, (II) 200 µm, and (III) 200 µm………………….101 Figure 4.17. The pore size distribution and average pore size of GO aerogel generated via aqueous GO suspension with an initial concentration of (a) 1 mg mL-1, (b) 3 mg mL-1, (c) 5 m g mL-1, and (d) 10 mg mL-1; the X-axis denotes the data point number with no specific order. The corresponding images can be seen in Figure 4.16……………………………………………….101 Figure 4.18. (a) Change in the volume of liquid templates and their corresponding macro-scale porosities upon changing the needle size from gauge 27 to gauge 15; the aerogels were prepared via injecting 2 mL of 10 mg mL-1 GO inks into the hexane domain containing 1 mg mL-1 POSS-NH2; the scale bar is equal to ~10.8 mm. FESEM images of aerogel filaments were generated via a needle with (b) gauge 27 and (c) gauge 15 with scale bars of (b) (I-III) 500 µm and (c) (I-III) 1 mm. Diameter distribution and average diameter of aerogel injected via a needle with gauges (d) 27 and (e) 15 into the POSS-NH2 domain; the X-axis denotes the data point number with no specific order………………………………………………………………………………...….102 Figure 5.1. A view of the VNA setup and its crucial parameters, adapted with permission from ref. 110……………………………………………………………………………………………….107 Figure 5.2. (a) Electrical conductivity of the aerogels after thermal annealing at 800 °C for 1 h under Ar, (b) the density of aerogels before and after thermal reduction. (c) Shielding coefficient, and (d) EMI shielding performance of the reduced aerogels within the X-band frequency range (8.2-12.4 GHz). (e) Schematic illustration of shielding behavior of multi-scale aerogel shields made of (I) reduced GO aerogel, (II) reduced GO-Fe aerogel, and (III) reduced GO-CNF aerogel. (f) The density-dependant shielding effectiveness of thermally annealed (800°C for 1 h under Ar) engineerable aerogels compared with recent practices in the field, and (g) comparing the total shielding and absorbance of the thermally reduced engineerable aerogels compared with recently xx developed shields; the reported values showcase the controllable shielding characteristics of the generated aerogels………………………………………………………………………..…….112 Figure 5.3. EMI shielding performance of (a-b) reduced GO aerogel, (c-d) reduced GO-Fe aerogel, and (e-f) reduced GO-CNF aerogel at port one and port two within the X-band frequency range (8.2-12.4 GHz); the uniform and nearly equal data from both ports show the reliability of the test and similar morphology of the aerogel at both sides……………………………………..…….113 Figure 5.4. (a) Digital image of (I) hydrophobic double-reduced GO aerogel and (II-III) its hydrophobicity assessment via sessile drop technique, (b) oil absorption performance of the double-reduced GO aerogels, (c) oil absorption rate over the density of absorbed oils, (d) oil absorption-desorption stability of the double-reduced GO aerogel, (e) prompt oil absorption-desorption cycle of double-reduced GO aerogel upon squeezing, (f) rapid absorption and separation of the used motor oil from the aqueous system via the double-reduced GO aerogel, and (g) oil absorption record of the as-developed aerogels compared with existing records; in the image, the overall amount of weight gain after oil absorption compared with the initial weight of the aerogel and the oil absorption enhancement is compared with the best practices in the field; the X-axis denotes the data point number with no specific order. Scale bars are equal to (a) (I) ~10.7 mm, (e) (I) ~9.4 mm, (II) ~9.8 mm, (III) ~10.1 mm, and (f) (I) ~9.2 mm, (II) ~9.1 mm, (III) ~9.1 mm. The reported scale bars in parts (a), (e), and (f) are approximate………………………….118 Figure 5.5. (a) Assembly of the piezoresistive sensor for human motion monitoring. (b) The cyclic piezoresistive sensing performance of rGO-CNF aerogel at different compressive strains (20-80 %). (c) Response and (d) recovery time of the assembled motion monitoring sensor. (e) Sensitivity of the developed piezoresistive sensor. (f) Touch sensing via the assembled sensitive motion monitoring sensor, and (g) the recorded signal for soft and hard touching of the sensor. (h) The recorded signal of swallowing as a subtle human body motion. Monitoring large body motion, including (i) contraction-relaxation biceps muscles and (j) knee movement. (k) The stability of the motion monitoring sensor before and after 1000 compression cycles through touching……………………………………………………………………………………...….125 Figure 5.6. (a) Schematic illustration of thermal insulation character of rGO-CNF aerogel placed on a hot plate along with the temperature gradient distribution, and (b) thermal insulation property of a 4 mm thick rGO-CNF aerogel over time; the insert shows the 2D temperature gradient distribution. (c) Infrared radiation blocking capability of a 4 mm thick rGO-CNF aerogel 30 cm, 20 cm, and 10 cm far from an incandescent heat lamp bulb. (d) The 2D temperature gradient distribution of the thermal radiation source and rGO-CNF aerogel. (e) Schematic illustration of the on/off heat generator made of rGO-CNF, (f) change of the induced temperature by the rGO-CNF aerogel upon changing the applied DC voltage, and (g) 3D temperature gradient distribution of the rGO-CNF aerogel upon switching on (4V DC) and switching off after 3s………………….…128 Figure 5.7. The capability of the reduced GO and reduced GO-CNF aerogels to maintain the body temperature……………………………………………………………………………….…….128 xxi Figure 5.8. The thermal insulation performance of non-reduced and reduced GO, and GO-CNF aerogels…………………………………………………………………………………...…….129 Figure 5.9. The heat generation performance of reduced GO-CNF aerogel upon applying voltage………………………………………………………………………………………….129 Figure 6.1. (a) Yielding free-standing filamentous aerogels through interfacial complexation; (I) pressure-adjusted extrusion of either GO or GO:CNF ink into the POSS-hexane domain to generate liquid templates, (II) freezing of the formed filamentous liquid template at -85 °C, (III) lyophilization of the frozen assemblies, and (IV) formation of 3D-structured aerogels. (b) Ultra-lightweight GO aerogel on a light leaf of a daffodil; scale bar is equal to ~ 13.39 mm, of note this image is taken by a digital camera and the scale bar is approximate. FESEM images of (c) rGO and (d) rGO-CNF aerogels; sub-parts showing (I) bulk aerogel construct, (II) macro-scale porosities between filaments (inter-filament porosities), and (III) micro-scale porosities within the filaments (intra-filament porosities); scale bars correspond to (I) 2 mm, (II) 1 mm, and (III) 100 µm. (e) The density of the aerogels before and after the thermal annealing (800 °C, 1 h under Ar). (f) The stress-strain curve of rGO-CNF aerogels at different compressive strains, i.e., 20 to 90 %, with six compression cycles at each strain. FESEM images of the 3D-structured filamentous GO-CNF aerogels extruded by needles with gauge numbers (f) 15 (inner diameter (I.D.) of 1.37 mm) and (g) 27 (I.D. of 0.21 mm). Scale bars are equal to (f & g) (I) 2 mm and (II) 500 µm…………………………………………………………………………………………...….139 Figure 6.2. (a-d) Extrusion of the (a) GO (10 mg mL-1) and (b) GO:CNF (1:1 weight ratio, 10 mg mL-1) inks into the POSS-hexane medium. Formation of liquid constructs made of (c) GO and (d) GO:CNF inks as a template for aerogel production. Scale bars are equal to (a) ~ 11.31 mm, (b) ~ 11.62 mm, (c) ~ 7.13 mm, and zoom area ~ 2.79 mm, (d) ~ 7.35 mm, and zoom area ~ 3.70 mm. The images demonstrated in parts (a) to (d) were taken by a digital camera, and their scale bars are approximate………………………………………………………………………………….….141 Figure 6.3. Dynamic interfacial tension of 1 mg mL-1 GO ink against the hexane-POSS medium………………………………………………………………………………...……….142 Figure 6.4. (a) Dynamic interfacial tension of the GO:CNF ink before and after the addition of POSS molecules as ligands. (b) The average interfacial tension of the GO:CNF ink against the hexane domain with and without POSS molecules. Contraction test of 1 mg mL-1 (c) GO and (d) GO:CNF ink in the extrusion medium (1 mg mL-1 POSS in hexane); the formation of the wrinkles around the droplets indicates the generation of robust assemblies at the interface capable of withstanding the applied forces and overcome the instabilities. This enables the liquid threads to preserve their integrity in a non-equilibrium filamentous form…………………………..…….143 Figure 6.5. Contraction of pendant drop related to 1 mg mL-1 GO:CNF ink (1:1 ratio) against pure hexane without POSS………………………………………………………………………..….143 xxii Figure 6.6. The average diameter of GO-CNF aerogels prepared via an injection needle with a gauge number of (a) 15 and (b) 27………………………………………………………..…….144 Figure 6.7. Pore size distribution assessment of the samples via FESEM analysis; the FESEM images of GO-CNF aerogels composed of (a) 5 mg mL-1 and (b) 10 mg mL-1 GO:CNF (1:1 weight ratio) at different zooms (I) 200x, (II) 300x, and (III) 400x. The pore size distribution and average pore size of the GO-CNF aerogel consisted of (c) 5 mg mL-1 and (d) 10 mg mL-1 GO:CNF (1:1 weight ratio), each obtained from the assessment of various spots of three different samples. The FESEM images showcase an obvious rise in the concentration of porosities per volume of the aerogel and a notable decline in the average pore size and pore size distribution upon an increase in the concentration of GO:CNF ink…………………………………………………………….145 Figure 6.8. X-ray diffractograms of aerogels before and after thermal annealing. Reprinted with permission from reference 109 under Creative Commons CC BY-NC 3.0 license. Of note, the baseline of the X-ray diffractograms was removed via further post-processing………….…….147 Figure 6.9. Micro-Raman spectroscopy results of aerogels before and after thermal annealing…………………………………………………………………………………….….148 Figure 6.10. (a) The electrical conductivity of the rGO and rGO-CNF aerogels. (b) The EMI shielding and (c) shielding coefficients of rGO-CNF aerogels at different ink concentrations (0.5 and 1 wt%) and thicknesses (2-6 mm). (d) The frequency-dependant EMI shielding of rGO-CNF aerogels over the X-band frequency range (8.2-12.4 GHz). Comparing small-sized and large-sized filament aerogels, including (e) EMI shielding and shielding parameters, (f) frequency-dependant EMI shielding over the X-band frequency range, and (g) shielding coefficients. (h) The absorbance (A) of the rGO-CNF aerogel (1 wt% ink, gauge 27, i.e., small-sized filaments) at different thicknesses compared with previously developed foams and aerogels; the corresponding data can be seen in Table 6.1. (i) The shielding mechanism of rGO-CNF aerogels with (I) large and (II) small filaments. As illustrated, declining the diameter of the filament in rGO-CNF aerogels increases the number of interfaces and porosities per volume of the aerogel, increasing the equivalent impedance and thereby minimizing the surface reflection. This alters the nature of the shield from dominant reflection to absorption………………………………………………….149 Figure 6.11. EMI SE characteristic of rGO-CNF aerogel prepared with 0.5 wt% ink at (a) 2 mm, (b) 4 mm, and (c) 6 mm thicknesses………………………………………………………..….152 Figure 6.12. EMI SE characteristic of rGO-CNF aerogel prepared with 1 wt% ink at (a) 2 mm, (b) 4 mm, and (c) 6 mm thicknesses……………………………………………………………….152 Figure 6.13. EMI SE characteristic of 6 mm thick rGO-CNF aerogel prepared with 1 wt% ink with (a) small and (b) large filaments…………………………………………………………….….152 Figure 6.14. (a) Aerogel EM trap’s mechanism of action, including (I) their pairing with superconductive metallic substrates, (II) blocking the induced reflections, i.e., secondary EM xxiii pollution, of metallic substrates and multiple reflections among inter-filament porosities, (III) interaction of EM waves with intra-filament porosities, including the multiple reflections between the skin and core of the core-shell filaments and multiple internal reflections within the porosity of the tubular porous core of aerogel’s filaments, (IV) interfacial and/or dipole polarization losses, and (V) conduction loss as a result of electron migration and hopping. The golden rods in parts IV and V represent the CNF, while blue and red spherics show positive and negative charges. (b) The EMI SE, and (c) the shielding coefficients of 6 mm thick rGO-CNF aerogels (1 wt%, gauge 27) with and without thin metallic foils/tape cover. EMI SE of the (d) rGO-CNF aerogels without any back cover and with (e) (I) 15 µm Al foil, (II) 15 µm carbon coated Al foil (C-Al foil), (III) 10 µm Cu foil, (IV) 50 µm Cu tape, and (V) 20 µm Ti foil, (VI) 426 µm Ti mesh, and (VII) 106 µm Zn foil within the X-band frequency range………………………………………………….……..154 Figure 6.15. (a) Shielding coefficients (reflectance (R) and absorbance (A)) and (b) shielding parameters (reflection loss (SER), absorption loss (SEA), and total specific shielding (SET)) of used metallic foils, mesh, or tape…………………………………………………………………….156 Figure 6.16. EMI SE of (a) Al foil (thickness (t):15 µm), (b) carbon-coated Al (C-Al) foil (t:15 µm), (c) Cu foil (t:10 µm), (d) Cu tape (t:50 µm), (e) Ti foil (t:20 µm), (f) Ti mesh (t:426 µm), and (g) Zn foil (t:106 µm) over the X-band frequency range (8.2-12.4 GHz) ……………………….157 Figure 6.17. The EM shielding performance of developed anti-reflection aerogels paired with metallic substrates compared with recent practices in the field; corresponding data can be seen in Table 6.4……………………………………………………………………………………..….158 Figure 7.1. (a) (I) Separated oil phase containing ligand (POSS-NH2) and an aqueous phase containing nanomaterials (GO and CNC) at desired concentrations before emulsification, and (II) the actual separated aqueous and oil phases containing nanoparticles and ligands, respectively; (b) (I) mixing and subsequent emulsification upon interfacial complexation, and (II) formation of emulsion gel. The scale bars in (a) (II) and (b) (II) are equal to 7.98 mm and 8.16 mm, respectively. These images were taken by a digital camera, and their scale bars are approximate. (c and d) A view of the jamming at the interface of the aqueous phase and oil droplets upon electrostatic interaction between the nanoparticles and ligands; herein, the blue rods show CNC, purple flakes show GO, and arrow-shaped objects in the droplets represent ligand (POSS-NH2). Confocal microscopy images of (e-g) GO1 CNC10 emulsion gel, in which the aqueous phase was stained with the calcofluor white stain; accordingly, the red phase showcases the presence of GO and CNC, while the black circles show the oil droplets containing ligands; the scale bars are equal to (e) 100 µm, and (f and g) 25 µm. Dynamic interfacial tension of (h) the neat water in hexane and GO1 CNC1 in hexane without any POSS-NH2, plus (i) GO1, CNC1, and GO1 CNC1 against hexane containing 1 mg mL-1 POSS-NH2. (j) Average interfacial tension before and after the addition of the ligand to the oil phase with or without the presence of various compositions of nanoparticles. (k) The contraction of the pendant drop and wrinkles formation, showcasing the jamming of the xxiv nanoparticles at the interface and formation of a solid skin as a result of overlapping assemblies of nanoparticles and ligands at the interface……………………………………………………….171 Figure 7.2. Rheological assessment of hydrogels and emulsion gels, including shear viscosity versus shear rate (flow curve) of (a) hydrogel and (b) emulsion gel; Gʹ and G" as a function of angular frequency (frequency sweep test) of (c) hydrogel and (d) emulsion gel; creep recovery test of (e) hydrogel and (f) emulsion gel…………………………………………………………….175 Figure 7.3. (a) The graphs of storage and loss moduli as a function of shear strain (the results of the frequency sweep data), (b) loss factor, and (c) complex viscosity versus angular frequency, (d) creep compliance as a function of time and (e) Gʹ and G" versus time (amplitude sweep tests or elastic recovery) of hydrogels………………………………………………………………..….175 Figure 7.4. (a) The graphs of storage and loss moduli as a function of shear strain (the results of the frequency sweep data), (b) loss factor, and (c) complex viscosity versus angular frequency, (d) creep compliance as a function of time and (e) Gʹ and G" versus time (amplitude sweep tests or elastic recovery) of emulsion gels……………………………………………………………….176 Figure 7.5. Formation of free-standing aerogel building blocks through (a) (I) freezing of the molded jammed emulsion gels and (II) their subsequent lyophilization yields a multi-scale porous aerogel with large pores made of stabilized oil droplets and smaller pores originating from the well-stacked GO flakes integrated with CNCs. FESEM images of free-standing aerogels made of (b) GO1 CNC1, and (c) GO1 CNC10; scale bars are equal to (b) 500 µm, and (c) 200 µm. (d) Free-standing non-reduced GO1 CNC1 aerogels standing on the light hairs of a cactus; the scale bar is equal to 7.87 mm; of note, this image was taken by a digital camera, and the scale bar is approximate. (e) Density variation of the aerogels upon increase in the CNC loading and their thermal annealing. (f) Volume shrinkage of aerogels after thermal annealing at different CNC loadings……………………………………………………………………………………...….177 Figure 7.6. The X-ray diffraction of non-reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels……………………………………………………………….….179 Figure 7.7. The X-ray diffraction of reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels……………………………………………………………………….180 Figure 7.8. Micro Raman spectroscopy of non-reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels, and reduced (e) GO1 CNC1, (f) GO1 CNC3, (g) GO1 CNC5, and (h) GO1 CNC10 aerogels……………………………………………………….….182 Figure 7.9. FTIR spectroscopy of non-reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels, and reduced (e) GO1 CNC1, (f) GO1 CNC3, (g) GO1 CNC5, and (h) GO1 CNC10 aerogels……………………………………………………………………….184 Figure 7.10. FESEM images of the (a) bulk free-standing non-reduced GO1 CNC1 aerogel and its (b-f) skin made of nanoparticle surfactants. Scale bars are equal to (a) 2 mm, (b) 500 µm, (c) 10 µm, (d-f) 5 µm……………………………………………………………………………….….185 xxv Figure 7.11. FESEM images of the (a) bulk free-standing non-reduced GO1 CNC10 aerogel and (b-f) the skin surrounding the aerogel made of nanoparticle surfactants. Scale bars are equal to (a) 2 mm, (b) 1 mm, (c) 500 µm, (d) 200 µm, (e) 100 µm, and (f) 20 µm……………………..….186 Figure 7.12. Stress-strain curves of (a) non-reduced and (b) reduced aerogels at various CNC concentrations. (c) A non-reduced GO1 CNC10 aerogel capable of holding a half-kilogram weight without any plastic deformation; the scale bar is equal to 13.22 mm; this image is taken by a digital camera, and the scale bar is approximate. (d) The elastic modulus of the reduced and non-reduced aerogels at different CNC loadings. (e) Cyclic compression of reduced GO1 CNC1 aerogels with six repeated compression cycles at different strains (20 to 70%), and (f) elastic resilience of the as-developed aerogels capable of undergoing large strains (80%) and recovering their shape with the least plastic deformations; the image shows the aerogels in (i) initial state, (ii) compression, and (iii) shape recovery upon force release. (g) The compressive cyclic stability of the reduced GO1 CNC1 aerogel after 100 loading-unloading compression cycles at the strain of 40%. (h) Change in the elastic modulus of the reduced GO1 CNC1 aerogel after 100 loading-unloading compression cycles. (i) The ultimate compressive strength of the as-developed aerogels compared with recent practices in the field by considering their lightness; of note, the unit of the x-axis is in logarithmic order…………………………………………………………………………………………….190 Figure 7.13. (a) The inability of the GO1 CNC10 emulsion gel to retain its shape fidelity upon DIW, and (b) the 3D-printable post-jamming ionically crosslinked GO1 CNC10 emulsion gel, capable of maintaining its shape and printing resolution because of the improved viscoelastic properties and shear thinning behavior. The scale bars are equal to (a) 13.30 mm, and (b) 9.84 mm; these images were taken by a digital camera, and their scale bars are approximate. The rheological characterization of the ionically crosslinked GO1 CNC10 emulsion gel (EG-Salt) and GO1 CNC10 emulsion gel (EG), including (c) shear viscosity a function of the shear rate, (d) Gʹ and G" against strain, (e) Gʹ and G" versus angular frequency, and (f) elastic recovery test. (g & h) Confocal microscopy images of the ionically crosslinked GO1 CNC10 jammed emulsion gel, showcasing the stability of the oil droplets in the aqueous phase and the stability of the emulsion system even upon a secondary ionic crosslinking by NaHCO3 salt……………………………………..…….195 Figure 7.14. (a) From 3D printing of the ionically crosslinked jammed emulsion gel to freezing and lyophilization for making aerogels with controllable spatial arrangement. (b) Ultra-lightweight 3D printed GO1 CNC10 aerogels with complex geometries standing on the light hairs of a cactus. FESEM images of the 3D printed aerogel grids from (c) macro-scale up to (d-e) micro-scale porosities. (f-g) FESEM images of 3D printed aerogels with complex geometries. (h) FESEM image of the reduced 3D printed GO1 CNC10 aerogel, and (i-j) EDX mapping of the reduced 3D printed GO1 CNC10 aerogel showing the dominant carbon content and the restoration of the conductive carbonaceous network; (k and l) FESEM images of the micro-scale porosities of the reduced 3D printed GO1 CNC10 aerogel, showcasing their shear-induced alignment. Scale bars are equal to (b) 10.02 mm, (c) 500 µm, (d) 50 µm, (e) 1 mm, (f) 1 mm, (g) 2 mm, (h) 1 mm, (i) 1 xxvi mm, (j) 1 mm, (k) 500 µm, and (l) 50 µm. The image in part (b) was captured with a digital camera, and the scale bar is approximate…………………………………………………………….….197 Figure 7.15. FESEM images from the 3D-printed filaments of ionically crosslinked GO1 CNC10, showing the uniform filament diameter. The scale bars are equal to (a) 1 mm and (b-c) 500 µm…………………………………………………………………………………………...….198 Figure 7.16. The average filament diameter of 3D-printed aerogels, printed by a needle with gauge number 30 (I.D. of 0.159 mm) ………………………………………………………………….198 Figure 7.17. FESEM image of the 3D-printed ionically crosslinked GO1 CNC10 aerogel grids with 3 mm in-fill distance showing (a-c) macro-scale porosities and (d) micro-scale porosities. Scale bars are equal to (a-c) 1 mm and (d) 500 µm…………………………………………….199 Figure 7.18. (a) FESEM image of the 3D-printed post-jamming ionically crosslinked GO1 CNC10 aerogel grids and (b-c) its EDX mapping……………………………………………………….200 Figure 7.19. EDX analysis of 3D-printed ionically crosslinked GO1 CNC10 aerogel……..….200 Figure 7.20. (a) FESEM image of the micro-scale porosity of 3D-printed ionically crosslinked GO1 CNC10 aerogel, and (b-c) its EDX mapping………………………………………..…….201 Figure 7.21. EDX analysis of the micro-scale porosity of 3D-printed ionically crosslinked GO1 CNC10 aerogel…………………………………………………………………….………...….201 Figure 7.22. (a) FESEM image of the triangular-shaped 3D-printed ionically crosslinked GO1 CNC10 aerogel and (b-c) its EDX mapping…………………………………………………….202 Figure 7.23. (a) FESEM image of the micro-scale porosity of triangular-shaped 3D-printed ionically crosslinked GO1 CNC10 aerogel, and (b-c) its EDX mapping……………………….203 Figure 7.24. FESEM images of thermally annealed (800 °C, under Ar for 1 h) 3D-printed GO1 CNC10 aerogels showcasing (a-c) macro-scale porosity and (d-k) micro-scale porosities. As demonstrated, applying the shear force to the emulsion ink led to the alignment of the GO flakes in the direction of printing. Scale bars are equal to (a) 2 mm, (b) 1 mm, (c) 500 µm, (d) 500 µm, (e) 500 µm, (f) 200 µm, (g) 100 µm, (h) 20 µm, (i) 10 µm, (j) 10 µm, and (k) 10 µm………….204 Figure 7.25. (a) FESEM image of thermally annealed 3D-printed chemically crosslinked GO1 CNC10 aerogel grids and (b-c) its EDX mapping……………………………………………….205 Figure 7.26. EDX analysis of thermally annealed 3D-printed chemically crosslinked GO1 CNC10 aerogel……………………………………………………………………………………….….205 Figure 7.27. (a) FESEM image of the micro-scale porosity of thermally annealed 3D-printed ionically crosslinked GO1 CNC10 aerogel and (b-c) its EDX mapping……………………….206 Figure 7.28. (a) The electrical conductivity of the free-standing aerogel after thermal annealing at 800 °C for 1 h under Ar at different CNC loadings; (b) shielding parameters, (c) shielding coefficients, and (d) frequency-dependant shielding behavior (in the X-band, 8.2-12.4 GHz) of the xxvii free-standing aerogel with an increasing CNC content. (e) Shielding parameters, and (f) shielding coefficients of 3D printed thermally annealed GO1 CNC10 aerogels at different thicknesses. (g) Shielding mechanisms of thermally annealed (800 °C for 1 h under Ar) (I) free-standing and (II) 3D-printed aerogels………………………………………………………………………….….209 Figure 7.29. EMI shielding performance of thermally annealed (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 free-standing aerogels within the X-band frequency range (8.2-12.4 GHz) …………………………………………………………………………...…….210 Figure 7.30. EMI shielding performance of thermally annealed 3D printed grides of GO1 CNC10 with (a) 1 mm, (b) 3 mm, and (c) 4 mm thicknesses…………………………………………….210 Figure 8.1. Feature cover photo of the Journal of Advanced Material, showing the potential of liquid-templated aerogels in making capable multi-scale porous shielding systems………………………………………………………………………………………….218 Figure 8.2. The feature cover photo of the Journal of Nanoscale, showing the potential of filamentous aerogels in blocking the incident and secondary reflected EM waves from the surface of metallic substrates……………………………………………………………………………220 xxviii List of Symbols S- Complex scattering parameters S1 Generated electromagnetic wave from port 1 S2 Generated electromagnetic wave from port 2 S11 Power ratio of the reflected wave over the incident wave at port 1 S22 Power ratio of the reflected wave over the incident wave at port 2 S21 Power ratio of the transmitted wave from port 1 to 2 over the incident wave at port 1 S12 Power of the transmitted wave from port 2 to 1 over the incident wave at port 2 dB Decibel R Reflectance T Transmittance A Absorbance PR Power of the reflected electromagnetic wave PI Power of the incident electromagnetic wave PT Power of the transmitted electromagnetic wave ET Transmitted electric field EI Incident electric field SET Total shielding effectiveness SER Shielding by reflection or reflection loss SEA Shielding by absorption or absorption loss SEM Multiple reflections loss ɳ Shield impedance ɳ0 Air impedances µ Magnetic permeability σ Electrical conductivity f Frequency of the incident electromagnetic wave α Attenuation constant ε Dielectric permittivity ω Angular frequency δ Skin depth G′ Storage modulus G′′ Loss modulus xxix τy Yield stress n Flow index k Consistency index  Shear rate η Viscosity S Siemens (unit of electrical conductivity) xxx List of Abbreviations 1D One dimensional 2D Two dimensional 3D Three dimensional AD Air-dried AgNWs Silver nanowires ANF Aramid nanofiber APEG Attractive Pickering emulsion gel BC Bacterial cellulose Bijel Bicontinuous interfacially jammed emulsion gel BPWP Biomass-derived banana peel waste paper CA Calcium alginate CEOS Aberration-corrector CF Carbon fabric CNC Cellulose nanocrystal CN Carbon nanofiber CNF Cellulose nanofibers CNT Carbon nanotube CuNWs Copper nanowires DDAB Didodecyldimethylammonium bromide DIW Direct ink writing EDS Energy dispersive spectrometer EM Electromagnetic EMI Electromagnetic interference FD Freeze-drying FDM Fused deposition modelling FESEM Field emission scanning electron microscope FGQF Ferromagnetic graphene quartz fiber FTIR Fourier-transform infrared spectroscopy GNR Graphene nanoribbon GO Graphene oxide GO-Fe3O4 Decorated graphene oxide with iron oxide nanoparticles xxxi GTR Ground tire rubber HRTEM High-resolution transmission electron microscope IFT Interfacial tension KF Kapok fiber Laponite Nanoclay mGO Magnetic graphene oxide MFC Micro fibrillated cellulose MWCNT Multi-walled carbon nanotube MXene Ti3C2Tx NFC Nanofibrillated cellulose NNC Native nanocellulose NPs Nanoparticles NPS Nanoparticle surfactants NWs Nanowires ODA Octadecyl amine O/W Oil-in-water emulsion PANi Polyaniline PCC Phase change capsules PDMS Polydimethylsiloxane PEDOT:PSS Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate PEG-DA Poly(ethylene glycol) diacrylate PET Polyethylene terephthalate PI Polyimide PLA Polylactic acid PLLA Poly(L-lactide) PMMA Poly (methyl methacrylate) PMSQ Polymethylsilsesquioxane POSS Polyhedral oligomeric silsesquioxane POSS-NH2 PSS-[3-(2-aminoethyl)amino]propyl-heptaisobutyl substituted PP Polypropylene PS Polystyrene PS-NH2 Amine-terminated polystyrene xxxii PU Polyurethane PVDF Polyvinylidene fluoride PVA Polyvinyl alcohol rGO Reduced graphene oxide SA Sodium alginate SAC Stearic acid chloride SD Supercritical drying SWCNT Single-walled carbon nanotube SSE Specific shielding effectiveness SSE/t Specific shielding effectiveness over thickness TEMPO 2,2,6,6-Tetramethylpiperidine 1-oxyl, 2,2,6,6-Tetramethyl-1-piperidinyloxy TOCNF TEMPO-oxidized CNF VD Vacuum-dried VNA Vector network analyzer WBF White bamboo fibril W/O Water-in-oil emulsion WPU Water‐borne polyurethane XG Xanthan gum XRD X-ray diffraction xxxiii Acknowledgment I would like to take a moment to express my deepest gratitude to my supervisor, Dr. Mohammad Arjmand, whose invaluable guidance and mentorship over the past few years have been the cornerstone of my academic journey. His profound expertise, unwavering support, and thoughtful feedback have not only shaped this thesis but have also profoundly influenced my growth as a scholar. His belief in my potential has been a constant source of motivation. My current accomplishments and the academic future I now envision would not have been possible without his kind support. I also want to express my sincere appreciation for the supportive efforts of various research groups in international institutions and universities that made the completion of this research study possible. I am deeply grateful to Professor Thomas P. Russell from the Department of Polymer Science and Engineering, University of Massachusetts Amherst and Lawrence Berkeley National Laboratory, Professor Mircea Dincă from the Department of Chemistry at Massachusetts Institute of Technology, Professor Seeram Ramakrishna from the Department of Mechanical Engineering, National University of Singapore, Professor Orlando J. Rojas from the Department of Chemical and Biological Engineering, the University of British Columbia, Professor Feng Jiang from Faculty of Forestry, the University of British Columbia, Professor Stefan Wuttke from Basque Centre for Materials, and Professor Abbas Milani from the School of Engineering at the University of British Columbia, Okanagan Campus. Their generosity, expertise, and guidance were instrumental in helping me navigate the complexities of this research study. Their insights, collaborative spirit, and encouragement have been invaluable in shaping the direction of my future scientific endeavours. I am truly fortunate to have learned from such esteemed scholars and to have had the opportunity to collaborate with them. xxxiv Dedication I dedicate this thesis to the love of my life, my beloved wife Mehrnoosh, for her unwavering support. To my cherished parents, my lovely mother Tahereh and my brave father Yahya, whose love and support have given me the foundation upon which I stand today. 1 Chapter 1: Thesis Organization & Key Argument The main objective of this thesis is to employ the art of interfacial complexation to yield engineerable multi-scale porous materials, viz., aerogels, toward advanced functions and designs with a primary focus on absorption-dominant electromagnetic (EM) shields. This engineerability starts with the formation of the structured liquid as a template for aerogel manufacturing, enabling controlling the features of the aerogel from nano-scale chemistry, micro-scale nanoparticle-surfactant assembly, and macro-scale aerogel manufacturing. The aerogels were manufactured in three main morphologies: filamentous, free-standing, and 3D-printed. Their porosity, morphological features, electrical conductivity, magnetization, and composition were optimized to control the EM shielding character of the developed porous constructs. In fact, I obtained a roadmap to boost the most effective EM wave dissipating parameters in porous constructs like aerogels to achieve a potent EM wave absorber. Interestingly, the engineerable nature of the aerogels also allows adjusting their composition and features toward a wide range of applications, starting from oil spill cleanup, piezoresistive sensing, thermal insulation, and infrared radiation blocking to Joule-heating. In the following sections, I will delve into the main motivation and stepwise progress of this research study toward potent functional porous constructs manufacturing with favourite structural integrity and mechanical properties. 1.1. Thesis motivation Aerogels, the lightest porous material made by mankind, provide remarkable opportunities for many crucial technological demands in today’s civilization. These demands include but are not limited to energy management, energy generation, solar-driven water desalination or atmospheric water harvesting systems, payload reduction in aerospace and aviation, and potent EM shielding 2 systems. Despite their excellent technological benefits, their widespread use is still limited because of some of their noteworthy drawbacks. Most traditional aerogels suffer from poor structural integrity and brittleness, making them inappropriate for real applications. Besides, owing to the nature of conventional sol-gel or gelation methods as templates for aerogel manufacturing, it's challenging to control the features, porosities, macro-scale morphology, or properties of the aerogels across scales while maintaining acceptable structural integrity. Additionally, improving the conductive domain of the aerogels to the levels required by advanced electronics or EM shielding systems poses another challenge because of the abundant micro-scale porosities within the aerogel structure. Addressing these challenges requires a clear technical roadmap, transforming the aerogel into potent technological building blocks. If an aerogel is optimized with proper porosities across multiple scales combined with adequate electrical conductivity and possible magnetization, it can act as a potent EM dissipator for shielding applications. This provides the possibility to boost the most effective EM wave dissipating parameters. Herein, our motivation is to develop a versatile aerogel manufacturing roadmap based on the interfacial complexation to address the conventional pitfalls of aerogels and transform them into formidable technological tools. The journey began with exploring the secrets of interfacial complexation and how to tune the composition, multi-scale porosities, features, and morphologies of the formed structured liquids, acting as engineerable templates for aerogels manufacturing upon freezing and lyophilization. The formed assemblies were further processed to make filamentous, free-standing, or 3D-printed aerogels with controllable morphology. Upon the engineerability of the design, the most effective EM dissipating parameters were boosted, leading to strong EM shields and EM wave traps, enabling the addressing of the most crucial challenges in the shielding science. Besides the shielding potentials, such a versatile roadmap could also be a 3 guideline to tune the features of aerogels toward a wide range of technological developments or advanced functions across various scientific disciplines, e.g., oil spill cleanup, piezoresistive sensing, thermal insulation, and beyond. 1.2. Research gap and objectives The primary goal of this thesis is to devise a versatile aerogel manufacturing roadmap toward advanced function and design with a primary technical focus on EM shielding. This attempt not only tends to address the traditional limitations of aerogel manufacturing but also creates a pathway to control the EM dissipating parameters, generating a shielding system with engineerable character, i.e., reflective or absorptive on demand. This demand becomes more and more crucial with the rapid pace of technological development and widespread use of EM waves in telecommunication systems, aviation, healthcare, the military, and beyond. This widespread use causes modern technological pollution, namely “electromagnetic interference (EMI)”. EMI can interact with sensitive electronics and adversely affect their proper function or jeopardize the health of vulnerable groups or living entities. To address this challenge, many efforts were put into action to develop shielding systems based on highly conductive materials. The first generation of this conductive material involves highly conductive metals such as copper, aluminum, or silver. Despite their excellent total shielding effectiveness, they pose another challenge associated with their surface reflections, causing secondary pollution as harmful as the incident EM waves. Besides, metals are heavy, and their bulkiness, along with their vulnerability to corrosion, spurred the need for their replacement. The newer generation of highly conductive shielding systems based on conductive polymers like Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) or 2D nanomaterials like MXene (Ti3C2Tx) can cover some of the disadvantages of neat metallic shields. However, they 4 show the same shielding mechanism as metals, viz., reflection, while some of them, like MXene, do not present a stable conductivity and lose their performance over a short period. This highlights the requirement for focusing on several key parameters to address the challenges of the shielding science (Figure 1.1): i) material selection, ii) assembly or processing methods to make a conductive porous structure out of the selected materials, iii) structural features and composition consideration, iv) mechanical properties and proper structural integrity of the resulting construct, and v) engineering the EM wave dissipating parameters to make potent shielding systems. Figure 1.1. Key parameters for manufacturing potent EM shielding aerogels. The main objective of the thesis is to develop an aerogel production roadmap based on interfacial complexation toward absorption-dominant shielding systems. The progressive steps have been considered as follows: Step I: From structured liquids to multi-scale porous aerogels This step involves yielding filamentous liquid templates employing interfacial complexation. The process starts with the extruding of an aqueous ink containing graphene oxide (GO) with other target nanomaterials into an oil phase consisting of an active ligand within hexane. Electrostatic interaction between the GO flakes and the ligands leads to the formation of nanoparticle surfactants (NPS), preserving the non-equilibrium filamentous form of extruded ink by overcoming the 5 instabilities. This serves as a template for aerogel manufacturing upon freezing and lyophilization. The engineerability of the process enables the control of aerogel features from nano-scale chemistry and micro-scale assembly to macro-scale manufacturing. Also, with the ability to customize the composition, filament size, processing conditions, and porosity across scales, we can optimize the design for the target application or function. Step II: Engineerable aerogels toward advanced function and design The second step involves optimizing the formed filamentous liquid templates toward controllable shields with absorptive or reflective character on demand. This allows for designing a versatile strategy to tune the shielding behavior of the filamentous aerogels based on demand. Additionally, as evidence of the approach's versatility and adaptability, the aerogels demonstrated exceptional performance across multiple applications, including record-breaking oil absorption, piezoresistive sensing, thermal insulation, infrared radiation blocking, and Joule heating. Step III: Aerogel electromagnetic traps: blocking the reflection of metallic substrates Step three involves maturing the shielding behavior of aerogels and developing anti-reflection aerogel electromagnetic traps. In this step, I showed that by reducing needle size during extrusion, aerogel with a smaller filament diameter can be obtained. This reduces the impedance mismatching, minimizes the surface reflections, and increases the EM wave dissipation within the aerogel, leading to absorption-dominant shielding systems. The manufactured aerogels effectively suppress surface reflections of metallic substrates, transforming them into highly efficient absorption-dominant shielding systems when paired with a highly conductive metal sheet. The outcome of this step addressed two of the main challenges of the shielding science: i) the need for 6 absorption-dominant shielding systems and ii) blocking the surface reflections of metallic substrates as a critical requirement for nearly all electronic systems. Step IV: Mechanically robust emulsion-templating shielding systems In the fourth step, I developed a versatile oil-in-water (O/W) emulsion templating process utilizing interfacial complexation to tackle one of the most significant challenges in aerogel design: achieving mechanically robust structures. This approach enables the making of ultra-lightweight aerogels with controllable mechanical properties (flexible or stiff on demand) combined with a controllable shielding character. Besides, I showed that via post-jamming salt complexation, we can control the rheological or viscoelastic properties of the emulsion gel, allowing 3D printing through direct ink writing (DIW). This gives the advantage of controlling the 3D-spatial morphology of the aerogel before freeze-drying. The outcome of the designed steps led to an aerogel manufacturing roadmap (Figure 1.2), enabling the generation of engineerable 3D-structured aerogels with the ability to control the density, porosity across dimensions, composition and nanomaterial concentration, mechanical properties, task-oriented functions, and EMI shielding mechanism to become either absorptive or reflective on demand. It is important to note that the general term "aerogel" is used throughout this study to refer to hierarchically porous structures, in alignment with common usage in the literature. While porous materials can be more specifically classified based on their drying methods, including i) xerogels (dried at room temperature), ii) cryogels (obtained via freeze-drying), and iii) aerogels (produced through supercritical drying), the term "aerogel" is employed here as a broad descriptor. 7 Figure 1.2. The schematic presentation showcases the main aim of this thesis to develop an aerogel manufacturing roadmap, enabling engineerable 3D-structured aerogels with control over their payload, porosity across dimensions, composition, mechanical properties, task-oriented functions, and EMI shielding mechanism. 1.3. Hypothesis, tasks, and outcomes: To accomplish this thesis according to the technological requirements and research gaps outlined in the previous sections, the following objectives, hypotheses, and tasks are considered to reach the expected outcomes. The detailed explanations are as follows: Objective 1: Designing an aerogel manufacturing roadmap to transition from interfacially driven structured liquids to multi-scale porous functional constructs. Hypothesis: I hypothesize that pressure-adjusted extrusion of an aqueous ink containing nanomaterials like graphene oxide (GO) with active carboxylic acid functionalities into a non-polar medium composed of hexane enriched with active amine-terminated ligands like PSS-[3-(2-aminoethyl)amino] propyl-heptaisobutyl substituted (POSS-NH2) leads to their complexation at oil (hexane)/water interface. This pH-driven interfacial complexation passes through the electrostatic interaction between the deprotonated carboxylic acid functional groups of 8 nanomaterials and protonated amine groups of ligands, forming the hybrid species of nanoparticle surfactants (NPSs) at the oil/water interface. This results in nanoparticles jamming at the oil/water interface, leading to a decline in the interfacial energy upon forming a robust skin at the interface. This skin preserves the integrity of the formed construct in a non-equilibrium shape via suppressing Plateau–Rayleigh instabilities. The result of this interfacial complexation is a structured filamentous liquid, which allows for customizable designs by adjusting the composition and processing parameters. The formed structured liquids can be used as a starting template for aerogel manufacturing via freezing and lyophilization, enabling control from nano-scale chemistry (through nanomaterial synthesis), micro-scale nanoparticle-ligand assembly (through interfacial complexation), and macro-scale aerogel manufacturing with engineerable morphological features. The whole process and its engineerable foundation can be considered a versatile aerogel manufacturing roadmap toward advanced technological functions. Tasks: This objective was initiated by synthesizing various nanomaterials like GO, cellulose nanofibers (CNFs), and magnetic GO (mGO) as the constituent building blocks of structured liquids and aerogels. Then, the structured liquids formation mechanism was thoroughly investigated, and their formation with customized composition, morphological features, characteristics, and stimuli-responsiveness was studied and optimized. The structured liquids were then used to manufacture various kinds of aerogels with on demand features and engineerable multi-scale porosities. Imposing a conductive domain into the porous network of the aerogels upon thermal annealing at 800 °C under Ar for 1 h enabled us to use them as potent EMI shields. As proof of functionality, the aerogels were also engineered for oil spill cleanup, piezoresistive human motion monitoring, thermal insulation, infrared radiation blocking, and Joule heating. 9 Outcome: The outlined objective has been successfully concluded, and the respective results are presented in Chapters 3, 4, and 5. Objective 2: Developing absorption-dominant anti-reflection aerogels Hypothesis: I hypothesize that by benefiting from the engineerable nature of structured liquid-driven aerogels, we can give rise to the most effective EM wave dissipation parameters and transform them into formidable shielding constructs. These parameters include multiple internal scattering of EM waves within the aerogel porosities combined with dielectric, magnetic, and conduction losses. Accordingly, reducing the size of structured liquid filaments can increase the number of interacting interfaces and facilitate impedance matching, allowing the penetration of EM waves into the aerogel with minimized surface reflections. Upon penetration of EM waves into the aerogel’s multi-scale porous structure, the EM waves undergo multiple reflections between the filaments and porosities in the core of aerogels, causing their dissipation in the form of heat. This could lead to the formation of absorption-dominant aerogels. The fabricated shielding aerogels can also serve as dissipators of electromagnetic waves reflected by metallic substrates, transforming them into absorption-dominant shields when paired together. This concept enables the development of "aerogel electromagnetic traps", which effectively block and dissipate the energy of incident and secondary reflected electromagnetic waves through absorption. Tasks: I first synthesized the required nanomaterials, including GO and CNF, to generate structured liquids with large and small filaments by changing the size of the injection needle during extrusion of the aqueous ink into the complexation medium, viz., POSS-NH2 enriched hexane. The formed structured liquids were then turned into free-standing hybrid GO-CNF aerogels, which underwent thermal annealing to make them electrically conductive. The optimized absorption-dominant shielding aerogels with small-sized filaments were thence used to block the surface 10 reflections of highly conductive metallic substrates made of copper, aluminum, titanium, and zinc upon pairing with them. Outcome: The outlined objective has been successfully concluded, and the respective results are presented in Chapters 3 and 6. Objective 3: Developing an emulsion-templated aerogel manufacturing approach to precisely engineer the morphological features, functionality, and mechanical properties of aerogels Hypothesis: One of the primary limitations of aerogels is their brittle nature and insufficient mechanical integrity and strength, which restrict their functionality. To address this, an advanced aerogel manufacturing strategy is needed to enhance their mechanical properties while minimizing the payload. I hypothesize that utilizing interfacial complexation and nanoparticle jamming can facilitate the formation of stable emulsion gels with tunable compositions and properties. Mixing GO with various CNC concentrations facilitates the formation of jammed emulsion gels. This process occurs through the complexation of nanomaterials with POSS-NH2 at water/oil droplet interfaces, resulting in the creation of hybrid emulsion gel templates. These emulsion gel templates could be used for multi-scale porous aerogel manufacturing, in which increasing the concentration of CNC can significantly enhance the strength of cell walls, leading to flexible or stiff aerogels on demand. Also, post-jamming salt complexation of CNCs with sodium bicarbonate enables the enhancement of the viscoelastic properties of emulsion gels without interrupting the jammed assemblies, making them 3D printable through direct ink writing (DIW). This allows controlling the macroscopic morphology of the aerogel’s template, making complex porous geometries with desired features and compositions. 11 Tasks: After synthesizing GO and procuring CNC, I made oil-in-water (O/W) emulsion gels in which the aqueous phase consisted of GO/CNC and the oil phase consisted of POSS-NH2 enriched hexane. I adjusted the CNC concentration while maintaining a fixed concentration of GO to fabricate free-standing aerogels with tunable mechanical properties, ranging from flexible to stiff, achieved through the freezing and lyophilization of the emulsion gel template. The rheological properties of the emulsion gels were thoroughly analyzed and compared with their non-complexed hydrogel counterparts composed solely of GO/CNC. Subsequently, salt complexation of CNCs within the continuous aqueous phase of the emulsion gel enhanced their viscoelastic characteristics, enabling 3D printing via direct ink writing (DIW). After the initial thermal annealing, the resulting free-standing and 3D-printed aerogels were effectively utilized for EMI shielding applications. Outcome: The outlined objective has been successfully concluded, and the respective results are presented in Chapters 3 and 7. 1.4. Thesis organization & scientific progress This thesis is organized into eight chapters, presenting a versatile approach to engineering the aerogel features toward advanced functions and designs with a specific focus on absorption-dominant EM shields. Our journey begins with Chapter 2, which summarizes i) the concept of structured liquids and their transition into free-standing aerogels, ii) the concept of shielding along with the beneficial role of aerogels, and iii) traditional and interfacially complexed aerogels fabrication processes and their use in EM shielding. In Chapter 3, I provide the nanomaterial synthesis recipes that include graphene oxide (GO), magnetic graphene oxide (mGO), and cellulose nanofibers (CNF). These nanomaterials served as the primary building blocks for the structured liquids, which functioned as templates for aerogel production. This chapter also 12 provides a comprehensive characterization of all synthesized nanomaterials to ensure they were fabricated with the desired properties and features. In Chapter 4, I introduce a versatile methodology to yield engineerable liquid structures through interfacial complexation as a template for aerogel manufacturing. The process starts with the extrusion of GO inks with or without other supporting nanomaterials, e.g., mGO or CNF, into a medium containing hexane and active ligands (POSS-NH2). Upon extrusion of the aqueous ink into the hexane/POSS-NH2 medium, the ligand and nanomaterials electrostatically interact at the interface and preserve the filamentous form of jetted liquids by suppressing the instabilities. This yields a filamentous structured liquid template in which the filament's diameter, composition, responsiveness, features, and functionalities can be tuned. These structured liquids act as engineerable templates for aerogel manufacturing via freezing and lyophilization. The controllability of the process allows precise regulation of features and porosities across multiple scales, while enabling the integration of conductivity and magnetization into the structure for advanced technological applications. This chapter primarily focuses on optimizing the process to achieve these capabilities. In Chapter 5, I showcase the potential of the designed methodology toward advanced applications with a specific focus on EMI shielding. By adjusting the composition, porosity, electrical conductivity, and magnetization of the fabricated filamentous aerogels, their shielding properties could be tailored to be either absorptive or reflective as needed. Furthermore, to demonstrate the functionality and engineerability of these aerogels, their potential for achieving record-high oil absorption, piezoresistive sensing, thermal insulation, infrared radiation blocking, and Joule heating was thoroughly evaluated. 13 In Chapter 6, I present the concept of "aerogel EM traps", highlighting optimized filamentous aerogels engineered to absorb the majority of incident EM waves while minimizing surface reflections when integrated with highly conductive metallic substrates. Interestingly, the shielding effectiveness of the resulting paired system synergistically combines the individual shielding capabilities of its components, resulting in an absorption-dominant EM shielding design with high total shielding effectiveness. This innovation addresses two longstanding challenges in shielding science: (i) the development of absorption-dominant shielding materials and (ii) the suppression of surface reflections from highly conductive metallic components, which are critical in many technological applications. This breakthrough enables the deployment of metallic shields while mitigating their harmful surface reflections, significantly enhancing their practicality and functionality. In Chapter 7, I introduce a methodology based on the oil-in-water (O/W) emulsion systems for aerogel manufacturing. The approach involves mixing fixed GO concentration with varying concentrations of cellulose nanocrystals (CNCs), followed by their subsequent mixing with hexane/POSS-NH2 medium. This leads to the formation of jammed emulsion gels, which serve as a template for aerogel manufacturing. Upon altering the concentration of CNC, I managed to change them from soft to stiffer aerogels, while their post-annealing at 800 °C under Ar turned them into an ultra-lightweight flexible aerogel with strong shielding capability. I also showed that via post-jamming ionic crosslinking, it is possible to enhance the rheological properties of the ink, enabling the 3D printing of the emulsion gels through direct ink writing (DIW). This allows controlling the 3D spatial arrangement of resulting aerogels with an aligned GO network in the direction of printing, increasing the electrical conductivity of the resulting construct. 14 In Chapter 8, I summarize the key findings of this thesis and outline future prospects and recommendations for advancing research on interfacial complexation in aerogel manufacturing. Figure 1.3 presents the roadmap developed and followed throughout this thesis, highlighting the major steps and milestones of the study. Figure 1.3. The planned roadmap for this thesis. 15 Chapter 2: Background & Literature Review This thesis explores the potential of interfacial complexation for creating engineerable structured liquids as templates for aerogel manufacturing. Given the critical role of structural engineering in electromagnetic interference (EMI) shielding and other advanced applications, I begin with a comprehensive discussion of the principles of interfacial complexation and its application in producing structured liquids in non-equilibrium states. I then examine various structured liquid systems and their transformation into free-standing porous materials. I continue the discussion with an understanding of the fundamentals and formulations of EMI shielding, focusing on the key parameters that contribute to effective EM waves’ absorption and shielding performance. Finally, I provide an overview of common aerogel manufacturing methods, highlighting recent advancements and their potential impact on EMI shielding. This chapter aims to offer a thorough understanding of the concepts presented in this thesis, emphasizing the creation of free-standing aerogels through the lens of interfacial science. 2.1. Structured liquids: Solid-like interfacial assemblies The assembly of solid particles and macromolecules at the liquid-liquid interface becomes even more interesting if we can engineer the interface to reflect solid-like behavior. Such a system can help us maintain non-equilibrium configurations of the immiscible liquids to generate a novel class of soft materials routinely called “structured liquids.” In practice, transitioning from the liquid-like or dynamic assembly of nanoparticles and macromolecules to solid-like behavior can be achieved through interfacial jamming.1, 2 Interfacial jamming typically happens when geometric constraints among neighbouring particles hinder their mobility at the interface, and even with dynamic forces at the liquid-liquid interface, the solid particles remain attached, i.e., pinned to the interface.3 For instance, when nanoparticles 16 become jammed at the interface, the temperature gradient and subsequent Brownian motion, which would typically displace nanoparticles in liquid-like assemblies with ease, are unable to eject them from the interface in a jammed system. This scenario is similar to experiencing traffic jams in a crowded city. During normal hours, with fewer cars on the street, maneuvering towards our destination is easy. However, during rush hours, when there are too many cars around us, changing lanes becomes difficult due to geometric constraints imposed by other vehicles, reducing our maneuverability. Similarly, interfacial jamming restricts particle mobility at the liquid-liquid interface, leading to solid-like behavior and maintaining non-equilibrium configurations.4 The concept of interfacial jamming and structured liquids has been explored through two primary pathways: the formation and jamming of nanoparticle surfactant (NPS) and the assembly of supermacromolecules at the liquid-liquid interface. In practice, interfacial jamming of NPSs can be realized when functionalized nanoparticles dispersed in one liquid interact with polymeric/oligomeric ligands with complementary functionality dissolved in a second immiscible liquid, forming NPS in situ. This process arrests the reduction in the interfacial area, stabilizing highly non-equilibrium shapes of liquids. On the other hand, supramolecular jamming involves the formation of a network of interconnected macromolecules at the interface. This structure offers the distinct advantage of creating an interface capable of resisting both compression and expansion, a capability not possible with nanoparticle-structured liquids.5 Up to now, these concepts have been used in designing a broad range of interfacially driven soft materials, including structured Pickering emulsions and emulgels,6 worm-like liquids,7 molded liquids,8 and to some extent, bicontinuous interfacially jammed emulsion gels (Bijels).9 In the following sections, we delve into the underlying mechanisms governing structured liquids, examining various morphologies designed based on interfacial jamming. 17 2.1.1. Nanoparticle surfactants: From discovery to direct evidence NPSs are a unique product of interfacial complexation, forming as a result of electrostatic interaction between nanoparticles with active functionalities in one liquid phase and ligands in another immiscible phase.10 This process was initially introduced by Russell and co-workers in which the interfacial interaction of an aqueous phase containing carboxylated polystyrene (PS) (diameter (D): 15 nm) was examined against an oil phase reinforced with amine-terminated polydimethylsiloxane (PDMS-NH2).10 In this system, NPSs were formed at the interface of the two immiscible liquids upon ammonium-carboxylated electrostatic interactions, capable of overcoming the weak interfacial forces governing the nanoparticles' interfacial adsorption. The mechanism of NPS formation at the interface of two immiscible liquids involves multiple processes, starting from the end-functionalized ligands diffusion to the interface, followed by the diffusion of nanoparticles from bulk toward the interface, and their subsequent assembly at the interface by electrostatic interaction between the nanoparticles and ligands. In the case of in situ formation of NPSs through electrostatic interactions, the final number of the anchored ligands to the nanoparticles at two immiscible liquid interfaces is self-regulated, acting in a way to reduce the interfacial energy as much as possible.11 Correspondingly, if the number of anchored ligands is too small, NPS assemblies would draw into the aqueous phase, whereas if the number of these ligands is too large, the NPS would draw into the oil phase, known as phase transfer.12-15 The packing of NPSs and their interfacial complexation can be controlled by tuning various parameters, including but not limited to i) concentration of nanoparticles and ligands, ii) the molecular weight of the amine-terminated polymeric ligands, iii) size of nanoparticles, iv) pH of the medium, and v) ionic strength of the aqueous phase.16-21 In general, an increase in the nanoparticles or ligand concentration highly contributes to minimizing the interfacial tension, 18 thereby stabilizing the liquid structures. It is also worth noting that aside from the concentration of the ligands, their size also affects the interfacial assembly and jamming of NPSs, especially in the case of polymeric ligands. For instance, in the case of amine-terminated polymeric ligands, by increasing the ligands’ molecular weight, their diffusion into the interface slows down. Therefore, the initial reduction in interfacial tension is much lower. Conversely, reducing the molecular weight of the polymer can lead to a significant decrease in equilibrium interfacial tension as individual polymeric chains become more effective in migrating to the interface.4 The formation of NPSs is also significantly influenced by the pH of the medium. This influence arises from the pKa values of the functional groups involved in electrostatic interactions. For instance, in a study by Russell and coworkers, the carboxylic acid group of nanoparticles and the amino groups of ligands have pKa values of approximately 4.2 and 9, respectively.10 When the pH of the medium is between the pKa values associated with the amine group of ligands and carboxyl functional groups of nanoparticles, the functional groups of nanoparticles get deprotonated while the amine functional groups of ligands get protonated. These deprotonated and protonated species undergo a strong electrostatic interaction that leads to interfacial complexation between nanoparticles and amine-terminated ligands. This process leads to NPS jamming at the interface, creating a thin solid layer capable of preserving the non-equilibrium shape of liquid constructs, facilitating the transition from liquid-like to solid-like behavior.4, 22, 23 However, if the pH value, for example, is lower than the pKa of carboxylic functional groups, these chemical moieties cannot undergo deprotonation, and as a result, we get no NPS formation and jamming at the interface. Therefore, pH is one of the strongest factors for controlling the NPSs assemblies and jamming in a system. 19 The ionic strength of the aqueous phase is another effective factor that can affect the interfacial packing of NPSs at the oil/water interface. Accordingly, an increase in the ionic strength could decrease the interfacial tension, increasing the density of disordered assemblies of the nanoparticles at the oil/water interface.19 So far, various types of NPS assemblies have been introduced and employed, preserving the non-equilibrium shape of liquid constructs through the jamming of NPS via a transition to solid-like behavior at the interface of two immiscible liquids. Table 2.1 tabulates a list of recently practiced interfacially driven systems based on the NPSs formation. Table 2.1. Recently developed nanoparticle surfactant (NPS) systems and the resulting liquid construct with a solid-like behavior. Liquid Construct Nanoparticle(s) Surfactant(s) Remarks Ref. Filamentous GO threads GO POSS-NH2 Liquid-in-liquid printing and streaming of aqueous GO ink into the silicone oil containing POSS-NH2. The interfacial complexation happens upon electrostatic interaction between the deprotonated carboxylic acid of GO and protonated POSS-NH3+ at the interface of two immersible liquids. 24 Filamentous GO threads GO POSS-NH2 Streaming of GO ink into the hexane containing POSS-NH2. 7 Filamentous emulsion GO threads GO POSS-NH2 Streaming of GO emulsion (O/W emulsion upon mixing hexane-enriched POSS-NH2 with an aqueous phase containing GO) into the hexane-POSS-NH2. 7 Filamentous GO threads GO POSS-NH2 Streaming of GO ink into the hexane-POSS-NH2. 25 Filamentous GO:MXene threads GO:MXene POSS-NH2 Streaming of hybrid GO:MXene ink into the hexane-POSS-NH2. The weight ratios of GO:MXene are 1:1 and 0.2:0.8. 25 MXene beads MXene POSS-NH2 Generating MXene liquid beads upon extruding 50 or 80 wt% MXene suspension into the hexane-POSS-NH2; the liquid beads form as a result of liquid stream break-up into discrete droplets. 25 Reconfigurable liquid structure of silica and CNC NPs Carboxylated silica, Carboxylated CNC PDMS-NH2 Liquid-in-liquid printing of aqueous suspension of carboxylated silica or CNC nanoparticles in the PDMS-NH2 enriched silicone oil, leading to reconfigurable and stimuli-responsive (pH-responsive) liquid structures. 26 Nanocaly liquid constructs Nanoclay PDMS-NH2 Streaming or liquid-in-liquid printing of nanoclay suspension into the PDMS-NH2 27 20 Liquid Construct Nanoparticle(s) Surfactant(s) Remarks Ref. enriched silicone oil, toluene, or hexadecane. Conductive PEDOT:PSS liquid constructs PEDOT:PSS PDMS-NH2 3D liquid-in-liquid printing of PEDOT:PSS ink into the PDMS-NH2 enriched silicone oil. 28 UV curable PEDOT:PSS liquid constructs PEDOT:PSS plus PEG-DA PDMS-NH2 Liquid-in-liquid printing of PEDOT:PSS ink with PEG-DA accompanied with a photo-curable component into the PDMS-NH2 enriched silicone oil. 28 CNC liquid letters CNC-OSO3- PS-NH2 Generation of the liquid letter upon interfacial complexation between the deprotonated CNC-OSO3- and protonated PS-NH2. 8 Filamentous CNC liquid constructs CNC PS-NH2 Streaming of CNC aqueous dispersion into the toluene containing PS-NH2, forming CNC liquid threads. 29 Liquid tubules or beads based on silica nanoparticles Carboxylated silica PDMS-NH2 Formation of tubules or bead-shaped liquids upon extruding aqueous dispersion of carboxylated silica nanoparticles into toluene-enriched PDMS-NH2. 30 Pickering emulsion gel Carboxylated silica PDMS-NH2 Formation of Pickering emulsion gel upon electrostatic interaction of carboxylated nanoparticles dispersed in the aqueous phase with 𝛼, 𝜔 -diamino functionalized polymers in the oil phase. The complexation happens at the oil/water interface. 6 3D printable GO/MXene emulsion gel GO and MXene ODA Formation of emulsion upon electrostatic interaction between the GO and MXene dispersed in the water phase and ODA in the oil phase (toluene), improving the viscoelastic character of the ink and allowing direct ink writing. 3 3D printable hybrid GO emulsion gel GO, CNC, or nanoclay DDAB Formation of 3D printable emulsion ink upon interfacial complexation between the negatively charged nanoparticles dispersed in the aqueous phase and DDAB in the oil phase. 31 Interfacially complexed Bijel arrangement Silica nanoparticles PDMS-NH2 Formation of Bijel upon mixing aqueous dispersion of silica nanoparticles and toluene containing two different molecular weights of PDMS-NH2 (1000 and 3000 g/mol). 9 Abbreviations: Graphene oxide (GO), aminopropylsobutyl polyhedral oligomeric silsesquioxane (POSS-NH2), oil in water emulsion (O/W), water in oil emulsion (W/O), Ti3C2Tx (MXene), mono-aminopropyl terminated poly(dimethylsiloxane) (PDMS-NH2), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), poly(ethylene glycol) diacrylate (PEG-DA), amine-terminated polystyrene (PS-NH2), octadecyl amine (ODA), didodecyldimethylammonium bromide (DDAB), and bicontinuous interfacially jammed emulsion gel (Bijel). 21 2.1.2. From nanoparticle surfactants to macro-scale structured liquids 2.1.2.1. Structured Pickering emulsions and emulgels The Pickering emulsion is known as a type of emulsion in which its stabilization passes through the adsorption of colloidal particles at the interface of two immiscible phases.32 The Pickering emulsion can be either water-in-oil (W/O) or oil-in-water (O/W) types based on the wettability of the particles. This can be described according to the contact angle of a solid particle at the oil/water interface.33, 34 In emulsion systems stabilized by solid particles, typically, one liquid wets the particles more thoroughly than the other, causing the less wetting liquid to become the dispersed phase. Accordingly, if the contact angle measured through the water phase becomes less than ˂ 90°, the particles are more hydrophilic, stabilizing the o/w emulsion systems. In contrast, at contact angles more than ˃90° where the particles are hydrophobic, the w/o emulsion will be stabilized.35, 36 Interestingly, employing the art of interfacial complexation in the Pickering emulsions provides the opportunity to stabilize the emulsion through the jamming of nanoparticles at the interface of two immiscible liquids. Additionally, structured emulsions facilitate the tailoring of viscoelastic properties and microstructures, enabling the creation of structured emulgels suitable for use in additive manufacturing.3, 6, 31 In this regard, attractive Pickering emulsion gels (APEGs) were obtained via electrostatic interactions between the nanoparticles stabilizing the water droplets and a telechelic polymer within the oil phase.6 In this approach, the water droplets are covered via negatively charged nanoparticles, i.e., carboxylic acid functionalized nanoparticles, providing active sites for electrostatic interaction with the positively charged telechelic polymeric ligands. Similar to typical NPS assemblies, this interaction is also based on the ammonium-carboxylated electrostatic interactions, in which telechelic polymeric ligands with two -NH2 ends interact with 22 two negatively charged nanoparticles in two neighboring aqueous droplets, bridging these droplets and facilitating the formation of APEGs (Figure 2.1). In such a system, the type of nanoparticles, oil phase, and telechelic polysemic ligands are customizable, providing a pathway to engineering the composition of APEGs on demand. Importantly, such a jammed system induces a strong viscoelastic and shear-thinning character, enabling the direct ink writing of the APEGs to yield customized 3D structures in the air or even under water. Of note, the rheological properties of APEGs can also be tuned by the molecular weight of the telechelic polymeric ligand, pH, and temperature, providing several opportunities for designing functional materials with controllable composition and rheological characteristics. Figure 2.1. (a) Formation of Pickering emulsion gel through the electrostatic interaction between the carboxylic acid functionalized nanoparticles in the aqueous phase and the 𝛼, 𝜔-diamino functionalized polymer as the colloidal surfactant in the oil phase; the displayed confocal microscopy image showcases the formation of Pickering emulsion gel in which the oil phase is stained with Nile Red. (b) Interfacial complexation and formation of Pickering emulsion gel through the electrostatic interaction between the negatively and positively charged nanoparticles and polymeric surfactant at the oil/water interface, starting from tailing and intra-droplet looping to inter-droplet bridging and looping. (a-b) Reproduced with permission.6 Copyright 2018, Wiley-VCH. 23 In another study, Zhang et al.31 developed viscoelastic Pickering emulsion gel through NPSs jamming at the interface. The formed Pickering emulsion gel consisted of negatively charged nanoparticles dispersed within the aqueous phase, i.e., cellulose nanofiber (CNF), graphene oxide (GO), and nanoclay (laponite), and didodecyldimethylammonium bromide (DDAB) as the ligand dispersed within the oil phase.31 The electrostatic interaction between the nanoparticles and ligands at the interface formed stable Pickering emulgels that stabilized the oil droplets within the continuous phase. In this system, the jamming of nanoparticles such as GO restricted the droplets and led to an increase in the viscosity and stiffness of the emulsion gel, leading to ideal printability. This also provides the possibility of homogeneous hybridization of non-water soluble and water-soluble nanoparticles at each respective oil and water phase, allowing for the customized composition and flexibility of design (Figure 2.2 (a)). It was evident that the GO stacking at the interface through jamming could improve the viscoelastic properties of the dispersions.37, 38 Upon an increase in the concentration of GO to more than 1 wt%, short distances among the GO flakes enhance their interactions, which are mainly based on hydrogen bonding, limiting their movement and mobility. This could also be accompanied by the steric hindrance of large GO flakes that restrict their movement upon jamming at the interface.38, 39 The jamming of the nanoparticles substantially reduces the spacing between the droplets, limiting their ability to deform and move. This restriction enhances the viscosity and stiffness of the emulgels, thereby improving their printability. In contrast to Pickering emulgels, which are designed using classical surfactants without interfacial jamming, NPSs formed through electrostatic interactions between nanoparticles in the aqueous phase and ligands in the oil phase can stabilize emulsion systems more effectively. This enhanced stability arises from the significantly higher binding energy of NPSs to the interface compared to 24 classical surfactants, thereby preventing droplet coalescence in emulsion systems. In this regard, Li et al.3 employed the art of interfacial complexation to yield 3D printable GO/MXene emulsion gel inks at low nanoparticle concentrations. The system is composed of low concentrations of GO (2.8 mg cm-3) and MXene (4.1 mg cm-3) in the aqueous phase, electrostatically interacting with the octadecyl amine (ODA) as the ligand in the oil phase (toluene), forming sheet-like NPS assemblies at the interface (Figure 2.2 (b)). In this system, the anchored ligand interactions among droplets dictate the rheological characteristic of the system, allowing a gel-like behavior with required viscoelastic properties toward direct ink writing at low 2D nanomaterials concentration. This happens upon reduction in the interfacial tension by electrostatic interactions between the nanoparticles and ligands at the interface, their subsequent jamming, and minimizing the interfacial area of the emulsion droplets.40, 41 This locks in the shape of the droplets within the continuous aqueous phase and forms stable emulsion gel with ideal viscoelastic behavior toward additive manufacturing. It is worth noting that the interfacial assembly of 2D GO and MXene and the viscoelastic characteristics of the resulting emulsion gel are spurred by a substantial reduction in Helmholtz free energy, which is contingent upon the geometry and shape of these nanoparticles.10 This suggests that a broader array of 2D nanomaterials, such as MoS2 or boron nitride, could potentially be employed to create emulsion gel systems in the future. 25 Figure 2.2. (a) From the formation of Pickering emulsion gel to 3D printing; step 1) emulsification of the aqueous phase containing nanoparticles and the oil phase containing ligand via homogenizer leading to Pickering emulsion gel formation; the jammed emulsion system provides the possibility to tune the viscoelastic character of the ink toward direct ink writing. Step 2) 3D printing of the jammed emulsion gel, controlling the spatial arrangement of 3D constructs. Step 3) crosslinking and reduction, and step 4) drying to yield a 3D structured construct with the ability to add water soluble and non-soluble nanoparticles in each water and oil phase, respectively. (a) Reproduced with permission.31 Copyright 2021, Nature Publishing Group. (b) Formation of emulsion gel through interfacial complexation of MXene/GO and octadecyl amine as the ligand, enabling direct ink writing and 3D structural design. The jamming process allows tuning the rheological and viscoelastic characteristics of the ink toward 3D printing. (b) Reproduced with permission.3 Copyright 2022, American Chemical Society. 26 2.1.2.2. All-liquid molding The robust NPS assemblies also provide a versatile and simple approach for the fabrication of 3D-shaped all-liquid molded constructs.8 In this method, adaptive and stimuli-responsive all-liquid structures are fabricated through molding and density-driven extraction of the formed liquid construct from the mold, in which the shape and details of the mold are preserved on the formed liquid objects. The sculpted liquid construct retains all the inherent characteristics of the constituent nanoparticles and preserves its 3D shape like a solid object, showcasing the potential of NPS in driving the liquid structures from liquid-like to solid-like behavior on demand. Notably, the approach enables a wide range of material selection for advanced functions and designs, providing a lot of opportunities for the next generation of smart soft materials. Importantly, from the technical perspective, the formation of all-liquid molded constructs is quite challenging due to several crucial criteria: 1) the binding energy that preserves the NPS assemblies at the interface must be high enough to retain their integrity, 2) the NPS assemblies formation must be faster than any relaxation of fluids, avoiding their deformation into equilibrium droplets, 3) the disordered interfacially driven elastic film generated from the jamming of NPS assemblies must be robust enough to suppress the instabilities during the removal of structured liquids from the mold and maintain the integrity of the liquid construct in a non-equilibrium form.4, 8 These criteria were satisfied through the prompt and strong binding of the cellulose nanocrystals (CNCs) with amine-terminated polystyrene (PS-NH2) at the oil/water interface, forming robust interfacially driven assemblies of cellulose nanocrystal surfactants (CNCSs).29 The turning point of CNCSs is their rapid and strong binding to the oil/water interface that could overcome the instabilities and retain the structural integrity of the liquid structures, paving the way for precisely designed 3D-structured all-liquid constructs.8 27 The all-liquid molding process starts from the placement of the CNC suspension into a predesigned mold, prewetted with an oil solution containing an amine-terminated polymeric ligand (Figure 2.3 (a)). Upon immersing the mold in the oil solution containing amine-terminated ligands, CNCSs rapidly form at the exposed interfaces, and the sculpted liquid constructs will be extracted from the mold because of the oil's higher density than the aqueous phase. Upon the extraction of the sculpted liquid construct from the mold, a decrease in the interfacial area will be initiated upon jamming of CNCSs assemblies at the interface, arresting the non-equilibrium shape of the molded liquid structure indefinitely. The electrostatic interaction of CNC and PS-NH2 ligand is pH-driven and occurs as a result of the complexation of the deprotonated sulfate group (−OSO3−, pKa of ≈1.9) of CNC and protonated amine group (−NH3+, pKa of ≈9.0) of PS-NH2, leading to disordered CNCSs assemblies at the interface and a dramatic decline in the interfacial tension. Accordingly, altering the pH of the medium can significantly affect the surface coverage of CNCSs assemblies, with higher surface coverage and structural stability at pH~3 (Figures 2.3 (b-c)). This enables reconfigurable all-liquid molded soft materials with ideal structural integrity and fidelity, e.g., complex geometries of alphabets with inherent mechanical robustness of NPS assemblies (Figure 2.3 (d)). Furthermore, the shape of the sculpted liquid objects can be altered via external stimuli by applying an electric field, external force, shear force, and varying the medium’s pH, 8 holding a great promise for developing smart and stimuli-responsive soft materials. 28 Figure 2.3. (a) The process of all-liquid molding, starting from (I) prewetting the mold with oil/ligand solution and placement of the CNC suspension in the mold. (II) Immersion of the mold into the oil/ligand solution and (III) its subsequent density-driven extraction from the mold. (b) Surface coverage of the CNCSs assemblies altered via the variation of pH. (c) Effect of pH on the shape fidelity of the molded liquid constructs, and (d) formation of molded liquid structured alphabets via the liquid molding strategy. (a-d) Reproduced with permission.8 Copyright 2018, Wiley-VCH. 2.1.2.3. Liquid streaming and 3D liquid-in-liquid printing Liquid streaming is a versatile approach wherein a jetted stream of one liquid within an external immiscible liquid can be stabilized through interfacial jamming by NPS assemblies, resulting in the formation of tubular liquid threads.9, 23, 42 To understand the potential of this approach, it is essential to explore what happens when a liquid stream is introduced into another immiscible domain, a phenomenon often elucidated by Plateau-Rayleigh instabilities. Upon streaming an aqueous liquid jet into a secondary immiscible liquid, the stream elongates and undergoes radius reduction after a specific distance. The jet’s elongation increases the surface area relative to I IIIII 29 volume, triggering periodic oscillations in the jet's diameter and the formation of curvature sites with concave and convex shapes. This causes an internal flux from areas with higher imposed pressure (concave area) to lower-pressure sites (convex area). This pressure gradient-induced flux declines the surface area on concave sites and increases the applied pressures and interfacial tension. As a result, the liquid stream breaks down into discrete droplets from these concave sites to overcome instabilities and reach an equilibrium by lowering the energy state.43 As a result, a jetted liquid within another immiscible liquid domain has been unable to produce filamentous structures or be used for 3D structural design via liquid-in-liquid printing. However, this limitation has recently been overcome by structuring a liquid jet through the interfacial assembly and jamming of NPSs, opening up numerous opportunities for further exploration in future studies.43, 44 Stabilized liquid streams have also been used in liquid-in-liquid printing to design complex all-liquid 3D geometries with on demand chemical or structural features. 10, 26 To this end, 3D liquid-in-liquid printing of an aqueous suspension of carboxylated nanoparticles into a highly viscous silicone oil containing amphiphilic amine-terminated polymeric ligands, i.e., amine-terminated polydimethylsiloxane (PDMS) was introduced (Figure 2.4 (a)).26 Interestingly, these printed structures are responsive to their external environment, i.e., pH, possess a tunable lifetime, and exhibit a compartmentalized response to chemical cues. As a result, such a construct can be used in applications ranging from liquid electronics and biphasic reaction vessels to cell or active material encapsulation platforms. Furthermore, reconfigurable all-liquid printed constructs have also been used to develop all-liquid microfluidic devices. In this regard, an assembly of NPSs, consisting of nanoclay and amine-functionalized PDMS, was used to create 3D all-liquid fluidic devices.27 This device features 30 spatially programmed functions and can be infinitely reconfigured (Figure 2.4 (b)). Employing 3D liquid-in-liquid printing, micropatterned 2D arrays were printed as channels for fluid flow. These channels are stabilized via a semi-permeable and anionic NPS membrane formed at the interface of liquids, allowing the on demand chemical exchange in the system. Besides, the anionic membrane of the device can be further functionalized with small cationic molecules, nanocrystal catalysts, and enzymes for a wide range of applications. Interestingly, the device could undergo multi-step chemical transformations in the induced microchannels, allowing selective mass transportation across the assemblies at the liquid-liquid interface for task-oriented separation. These microfluidic devices can be automated using detectors, pumps, and appropriate control systems, demonstrating potential capabilities for learning and recognizing chemical logic (Figure 2.4 (c)). In another attempt, conductive structures of poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) were fabricated through 3D liquid-in-liquid printing, where an aqueous suspension of PEDOT:PSS was injected into an oil phase containing PDMS-NH2 as a ligand. In this process, the colloidal PEDOT:PSS particles, consisting of a hydrophobic PEDOT core with a hydrophilic shell, electrostatically interact with the protonated amine group of PDMS-NH3+ via the deprotonated sulfonate group R-SO3- of PSS upon injection into the ligand-enriched oil phase. This results in the formation of an elastic skin at the interface, which stabilizes the threads and maintains their non-equilibrium filamentous shape (Figures 2.4 (d-e)). To improve the mechanical strength of these conductive liquid threads, poly(ethylene glycol) diacrylate (PEG-DA) was added to the aqueous phase and crosslinked by being irradiated under 395 nm UV light. This approach enables the creation of mechanically robust and electrically conductive liquid structures suitable 31 for biomedical applications, as well as customizable electro-microfluidic devices designed for implanting biochips for near-field communication within living organisms.28 Figure 2.4. (a) Liquid-in-liquid printing of aqueous phases containing carboxylated nanoparticles into highly viscous silicon oil. This method generates liquid constructs with a pre-defined 3D architecture upon NPS formation and creation of an elastic film at the interface. (a) Reproduced with permission.26 Copyright 2018, Wiley-VCH. (b) Schematic illustration of an all-fluidic device fabricated through interfacial complexation of nanoclay and polymeric surfactant, holding the integrity of the liquid constructs and allowing the flow of fluids through the channels. (c) The disconnection of microchannels in all-liquid microfluidic devices is possible by simply cutting the bridged connections. (b-c) Reproduced with permission.27 Copyright 2019, Nature Publishing Group. (d) Liquid-in-liquid printed constructs with tunable electrical conductivity, mechanical robustness, and morphology; the 3D printed threads form upon extruding the PEDOT:PSS-based aqueous suspensions into an oil phase enriched with amine-functionalized PDMS. (e) Schematic illustration of PSS-stabilized hydrogel threads within ligand-enriched silicone oil after UV curing of the acrylate monomer. (d-e) Reproduced with permission.28 Copyright 2023, Nature Publishing Group. 2.1.2.4. Bicontinuous interfacially jammed emulsion gels (Bijels) Bijels are non-equilibrium emulsion systems where two immiscible liquids’ interpenetrating domains are stabilized through interfacial colloidal monolayers.45, 46 The formation of Bijels was initially predicted through simulations, which suggested the possibility of generating this class of 32 soft materials through demixing and spinodal decomposition (phase separation). This process creates interpenetrating domains of two liquids with an extensive interfacial area, forming a fluid labyrinth where each liquid phase connects one side of the sample to the other. In such a system, the interpenetrating domains of liquids are arrested in place by the adsorption of a layer of colloidal nanoparticles onto the liquid-liquid interface. In the context of Bijels, spinodal decomposition describes the process of phase separation where two immiscible fluids naturally separate into distinct regions due to thermodynamic instability caused by changes in the chemical composition or temperature of the system. This phenomenon results in the formation of tortuous or interconnected domains of liquids, as previously discussed. However, achieving and maintaining Bijels through this mechanism poses significant challenges, requiring two key considerations: 1) The first consideration involves selecting particles that are neutrally wettable by both liquid phases, ensuring a contact angle of 90° to prevent curvature imposition on the liquid-liquid interface during phase separation. 2) The size of nanoparticles used to stabilize the complex interfaces within the Bijel domain is also crucial. Small nanoparticles (<50 nm) have lower binding energies to oil/water interfaces, especially in Bijels with low surface tensions, limiting their ability to solidify the non-equilibrium interface shapes.47-49 In the context of demixing and spinodal decomposition in an oil/water/surfactant system, it is crucial to determine the proportions of each component to achieve bicontinuous systems instead of forming oil-in-water or water-in-oil emulsion droplets. To accomplish this, triangular pseudo-ternary phase diagrams should be created for such systems (Figure 2.5). These diagrams serve as technical maps that depict the emulsion's phase behavior, stability, properties, and droplet size.50 As illustrated in Figure 2.5, the apex of the triangular phase diagram represents the pure component (100%), gradually decreasing to 0% as it approaches the opposite apex, where the other component 33 is at 100%. This diagram is typically generated using the water titration method, where fixed weight ratios of the surfactant are mixed into either the oil or water phase and then added to the opposite phase at varying ratios (w/w). The resulting phase diagram provides a visual guide to observe spinodal decomposition at specific oil/water/surfactant ratios. This observation helps determine the likelihood, type, and characteristics of the emulsions formed at different compositions of oil/water/surfactant.50, 51 As illustrated in Figure 2.5, the triangular phase diagram delineates several distinct regions: Side A represents a water/surfactant binary system, indicating the likelihood of oil-in-water (O/W) emulsion formation due to an abundance of water and limited concentrations of oil and surfactant. This configuration results in micelles with hydrophilic groups oriented outward, situated within the water phase. Side B depicts an oil/surfactant binary system, showcasing the highest probability of water-in-oil (W/O) emulsion formation. Here, reverse micelles with hydrophobic groups positioned outward within the oil phase are predominant. Side C illustrates the water and oil binary system with minimal surfactant content, leading to the presence of multiple phases with decreased stability. The upper apex corresponds to the maximum surfactant concentration and minimal water or oil content, resulting in surfactant molecules adopting a lamellar morphology to prevent emulsion formation. Finally, the bicontinuous phase represents the desired region for Bijels, where a bicontinuous structure will form, characterized by interpenetrating domains of both water and oil phases. These delineations offer insights into the phase behavior and emulsion formation tendencies within the oil/water/surfactant system, aiding in the design and understanding of complex emulsion structures.50, 52 34 Figure 2.5. (a) Schematic illustration of ternary phase diagram showcasing diverse emulsion states. (a) Reproduced with permission.50 Copyright 2021, Elsevier. (b) Ternary phase diagram showing the formation of oil in water (O/W), water in oil (W/O), or bicontinuous emulsion upon changing the concentration of oil, water, and surfactant with respect to each other. (b) Reproduced with permission.52 Copyright 2021, American Chemical Society. Using NPS assemblies, Russell and co-workers developed a scalable and facile approach for generating macroscopic Bijel assemblies with a tunable internal feature size in sub-micrometer scale (˂5 µm).9 In such a system, the jammed emulsions are tortuous, showing interconnected constructs of two immiscible liquids that are kinetically arrested by colloidal nanoparticles, irreversibly bonded to the oil/water interface. Instead of spinodal decomposition, this type of Bijels with sub-micron domains can be generated via homogenization. As a result, the system arrests the bicontinuous assembly at the liquid decomposition point through electrostatic interaction between the ligand dispersed in toluene (PDMS-NH2, with molecular weights of 1000 and 3000 g mol-1) and carboxylated nanoparticles in the aqueous phase, occurring at the liquid-liquid interface. This process locks in the non-equilibrium bicontinuous toluene/water system through NPSs jamming at the interface (Figure 2.6). Interestingly, the developed approach is simple and scalable, capable of generating bicontinuous arrangements upon vigorous shaking of the oil/water system, where the domain size (1-10 µm), stability, and structure of the Bijels can be altered by customizing the 35 constituent components, i.e., nanoparticles, polymeric ligand, and liquids. This shows significant potential for the development of reconfigurable bicontinuous liquids on an industrial scale, which can be reshaped as desired with an external field. Figure 2.6. Bijel formation via NPS assemblies; (a) schematic illustration of Bijel formation by NPSs jamming at the oil/water interface. (b) Stabilized emulsion system based on PDMS-NH2 dissolved in toluene with molecular weights of (i) 1000 g mol-1 and (ii) 3000 g mol-1 plus an aqueous phase containing 1 mg ml-1 carboxylated nanoparticles. (iii) Bicontinuous arrangement of toluene/water system arrested via NPS assemblies with equimolar PDMS-NH2 with a molecular weight of 1000 and 3000 g mol-1 at nanoparticle concentration of 0.5 mg ml-1. (c) Formed NPS assemblies with nanoparticle concentrations of (i) 0.1 and (ii) 0.5 mg ml-1 at a fixed PDMS-NH2 concentration. Arrangement of the bicontinuous network at a fixed nanoparticle concentration of 1 mg ml-1 and variable PDMS-NH2 concentrations of (iii) 0.161 and (iv) 16.1 mmol L-1. As can be seen, a change in the nanoparticle or ligand concentration can significantly affect Bijel’s arrangement. (a-c) Reproduced with permission.9 Copyright 2017, Nature Publishing Group. 2.2. EMI shielding fundamentals and mechanism Design and development of potent EM shielding systems require an in-depth understanding of the mechanism and fundamentals of the shielding science. To this end, the interaction between the incident EM waves and the surface/interior of an EM shield can be categorized into reflection, absorption, and multiple reflections. Based on the morphology and material selection of the EMI shields, another shielding mechanism, referred to as internal scattering or multiple internal 36 reflections, can also be adopted to describe the EMI shielding behavior of a structure. The primary shielding mechanism is the reflection that happens due to the impedance mismatch between free space and the electrically conductive material used for shielding 53-56. The wave impedance of an EM wave is the ratio of the transverse components of the electric and magnetic fields, and its value for free space is around 377 Ω. However, in highly conductive materials, the impedance is much lower, showing the inability of EM waves to propagate through conductive materials. In this case, the energy of EM waves transfers to the electrons and free-charged particles within the shield and forces them to oscillate. The enforced oscillating charges create a scattered or induced field known as reflection. Highly conductive materials (e.g., metals, graphene, MWCNTs, MXene, and conductive polymers) are traditionally employed for various EMI shielding applications 53-56. It is also worth noting that reflection happens at the surface of EMI shielding materials and mainly relies on the electrical conductivity of the structures 7, 56. Aside from reflection, the energy of EM waves also dissipates in terms of heat while interacting with the shielding materials. This secondary shielding mechanism is called absorption, which happens in the material with electrical or magnetic dipoles and finite electrical conductivity 56, 57. Beyond this point, a portion of the incident wave may pass through the shielding material (transmission). Multiple reflections and internal scattering mechanisms also affect the shielding behavior of a material. These two concepts are often mistakenly confused with each other in previous studies 58, 59. Multiple reflections happen at thin EMI shields (Figure 2.7 (a)). In this case, the wave that has already passed through the front interface of a thin shield might be reflected from the back interface and move toward the front interface, where a portion of the wave exits the shield and the rest re-reflects inside to contribute to the second transmission. Multiple reflections repeatedly occur until the wave's energy is completely dissipated, as the wave travels back and forth through the thin 37 EMI shields. Multiple reflections are highly dependent on the thickness and become negligible at a thickness close to or larger than the skin depth (the distance beneath the surface at which the intensity of the electric field decreases to e-1 of the original incident wave intensity). However, if the thickness of a thin EMI shield is significantly smaller than the skin depth, multiple reflections between the front and back of the shield will lower the shielding effectiveness of the material 56, 60, 61. On the other hand, internal scattering, also called internal multiple reflections, happens within materials containing numerous internal interfaces (e.g., aerogels and foams, multi-layered shields, and segregated structures). In contrast to multiple reflections, internal scattering can significantly enhance the shielding effectiveness of a material. In this case, interfaces with mismatching impedance contribute to the multiple back-and-forth reflections inside the shield, extend the propagation path length of the waves before transmission, and provide a higher chance of interaction between the shield and the waves. These back-and-forth reflections eventually tend to dissipate the energy of the waves in terms of heat and contribute to higher absorption. The internal scattering of the waves in aerogels and foams, multi-layered shields, and segregated structures is schematically shown in Figure 2.7 (b-d). Of note, the internal scattering should be distinguished from multiple reflections. Internal scattering happens due to the numerous internal interfaces inside the shield, which trap the waves inside the structure until their energy dissipates in the form of heat. However, multiple reflections occur between the front and back interfaces of a thin shield and enhance the chance of waves exiting the shield, reducing the shielding effectiveness 56, 60, 62, 63. 38 2.2.1. EMI shielding measurements and scattering parameters In the field of EMI shielding, the two-port vector network analyzer (VNA) is widely used for characterizing the shielding effectiveness. In this method, the samples are sandwiched between two flanges that are connected to the waveguides of the VNA (Figure 2.7 (e)). For each measurement, the system sends a signal from port one (S1) at a single frequency to the sandwiched sample. The receivers detect the reflected (S11) and transmitted (S21) waves, and the magnitude and phase data of each signal are then measured. After the same signal is sent to the sample from port two (S2) with the same frequency, the new reflected (S22) and transmitted (S12) waves are detected by the receivers. When the source shifts to the next frequency, the new measurements are made again. In the end, the reflection and transmission measurements are presented in terms of complex scattering (S-) parameters. It is important to point out that the homogeneity of the sample results in equal values for S11 and S22 together, as well as S21 and S12 together 64. The scattering (S-) parameters are used to calculate the EMI shielding coefficients, namely, reflectance (R), absorbance (A), and transmittance (T). The underlying EMI shielding mechanisms can be accurately evaluated based on these EMI shielding coefficients. The power of the reflected wave (PR) over that of the incident wave (PI) is defined as the R coefficient. The following equation can be used to calculate R based on the complex S11 parameter 65: R =PRPI= |𝑆11|2 = |𝑆22|2 (2.1) Where S11 is the complex scattering parameter that is measured based on the reflected voltage magnitude divided by the incident voltage magnitude in port S1. On the other hand, the power of the transmitted wave (PT) over that of the incident wave is the T coefficient, which is calculated based on the complex S21 parameter 65: 39 T =PTPI= |𝑆12|2 = |𝑆21|2 (2.2) Where S21 is the transmitted voltage magnitude from port 1 to port 2 divided by the incident voltage magnitude in port 1. Finally, the A coefficient is calculated based on the following equations 65: A = 1 − R − T (2.3) 2.2.2. Shielding effectiveness Aside from shielding coefficients, the shielding effectiveness, also known as the total EMI shielding effectiveness (SET), is routinely used to investigate the performance of a shield. SET is the effective protection of a shield against incident EM waves, which is defined as the ratio of the transmitted and incident powers of EM waves on a logarithmic scale. The respective formula can be expressed as follows 65: SET(dB) = 10logPIPT= 20logEIET (2.4) where P and E correspond to the power intensity and intensity of the electric field, respectively. The subscripts T and I show the transmitted and incident EM waves, respectively. Based on the Schelkunoff’s theory, SET is the sum of attenuation resulting from the reflection loss (SER), absorption loss (SEA), and multiple reflections loss (SEM) 66-69: SET = SER + SEA + SEM (2.5) The magnitude of the SER from the front or back sides of the shield could be accurately quantified by using the simplified version of Fresnel’s equation for a conductive shield, which can be defined as follows 60: SER(dB) = 20log(ɳ + ɳ0)24ɳɳ0 (2.6) 40 SER(dB) = 39.5 + 10logσ2πfμ (2.7) SER(dB) = 10 log (11 − R ) (2.8) Where ɳ and ɳ0 correspond to the shield and air impedances in Ω, respectively; µ and σ are attributed to the magnetic permeability and electrical conductivity, respectively, and f is the incident EM wave’s frequency in Hz. In this regard, SER has a direct relationship with the electrical conductivity of the shield, and upon increasing the electrical conductivity, the reflection loss will improve accordingly. Besides electrical conductivity, the frequency of the incident EM waves and the magnetic permeability of the shield also play a crucial role in the magnitude of the reflection loss 60. An incident EM wave will be attenuated upon its propagation in a lossy medium with electrical or magnetic dipoles and finite electrical conductivity. Reaching a high rate of EM wave attenuation requires several conditions, including finite electrical conductivity for effective ohmic losses that contribute to the interaction between the incident EM waves and electrons in the shield 70, high dielectric permittivity for effective dielectric losses that happen due to the generation of multiple micro-/nano-capacitors 71, and high magnetic permeability to boost magnetic losses associated with the eddy current loss and magnetic hysteresis loss 72. The absorption loss or SEA can be calculated based on the following equations: SEA(dB) = 20logeαd = 20 (dδ) log10 e = 8.68 (dδ) = 8.7d√πfμσ (2.9) SEA(dB) = 10 log ( 1 ― R T ) (2.10) Where δ corresponds to the penetration depth or skin depth in µm. This parameter is crucial in shielding and expresses the distance beneath the surface of a shield at which the intensity of the 41 electric field decreases to 1/e of the original intensity of an incident EM wave. For a conductive EM shield, the skin depth can be measured via the following equation 65: δ = (√πfσμ)−1 (2.11) Based on the equation related to SEA, both the electrical conductivity and thickness improve the absorption rate, whereas permeability and permittivity are used to determine the absorption loss. In a thin shield with a small thickness, reflection from the back interface of the shield affects the final transmission because of the multiple reflections, as the reflected EM waves re-reflect at the front surface and lead to a second transmission. It is worth noting that multiple reflections between the front and back surfaces of a shield contribute to a lower value of SET. The multiple reflection loss or SEM can be calculated via the following formula 65: SEM(dB) = 20 log10(1 − e−αd) = 20 log10 [1 − e−2dδ ] (2.12) SEM depends on the thickness of the shield, and it becomes negligible at a thickness larger or close to the skin depth (δ) when the SET reaches values higher than 15 dB. When the thickness becomes smaller than the skin depth, the multiple reflections become a significant attenuation parameter. Therefore, it is vital to consider the value of multiple reflections in such cases to measure the total EMI shielding effectiveness of a material precisely. Lightweight shields are highly sought for designing an effective shielding material, especially for applications such as compact electronics and aerospace. The specific shielding effectiveness (SSE) over thickness (SSE/t) is a parameter that considers both the density and thickness of a shield. SSE (in dB cm2 g-1) can be measured by dividing the SET (in dB) by the thickness (in cm) and density ρ (in g. cm−3). This important parameter can be calculated as follows 65: 42 𝑆𝑆𝐸/𝑡 =𝑆𝐸𝑇ρ ∗ t (2.13) 2.2.3. Evaluating the dominant shielding mechanism: basic concepts and a common mistake The dominant shielding mechanism of a shield should be evaluated based on the ratio of the incident power to the reflected and transmitted power of EM waves. However, some of the recently published studies used the ratio of SEA and SER to report the dominant EMI shielding mechanism of various compounds 58, 59. Typically, these studies have stated incorrectly that if SEA>SER or SEA/SER>1, the dominant shielding mechanism will be absorption. Nevertheless, it is entirely wrong to assess the shielding mechanism based on the ratio of SE parameters since their values are logarithmic ratios of powers and should not be used to examine the amount of absorbed or reflected incident EM waves by a shield 53. Calculations used for the absorption loss (SEA) demonstrate that the ratio of SE values should not be used to evaluate the dominant EMI shielding mechanism of a material (Equations 10 and 11). In a typical EMI shielding measurement setup, the scattering parameters are recorded and converted to the shielding coefficients (R, A, and T). Based on the measured shielding coefficients, the value of SEA is calculated to be 10 log ( 1− R T ). According to this equation, SEA is the ratio of the wave that penetrates the shield (after deducting the reflectance from the incident waves) over the transmittance and is not a direct representation of the ratio of the incident wave over the reflected or transmitted wave. Hence, EMI shielding coefficients should be used to evaluate the dominant shielding mechanism of a material. Accordingly, if the value of R becomes higher than A for a material, the dominant shielding mechanism is reflection. This can be translated to R>0.5 or SER>3dB, as shown in Figure 2.7 (f). Such a mechanism can be observed for highly conductive materials, which mainly happens due to the impedance mismatch and causes unfavourable 43 secondary reflections. However, in a shield with a dominant absorption mechanism, the value of A is higher than R (R<0.5 or SER<3dB). 2.2.4. EMI shielding mechanisms of fibrous and porous materials The dominant EMI shielding mechanism of a shielding system strongly depends on the types of materials, fabrication process, and morphology of the construct. In this section, we considered several types of shielding structures including: (i) electrospun fibers/mats, (ii) layered fibrous structures, and (iii) aerogels, to provide in-depth insight into differences in the shielding mechanism of diverse structural designs. Accordingly, most of the electrospun fibers/mats shields are mainly built of conductive nanocomposites, translating into a high R coefficient (R>0.5) and reflection-dominant shielding mechanism. The electrospun shields of polyacrylonitrile fibers decorated with Ag seeds 73, polyaniline (PANI)/polyethylene oxide (PEO)/MWCNTs 74, TaC/Fe3C/C 75, and polyacrylonitrile/Ag nanoparticle 76 were all characterized by > 50% reflectance, presenting reflection-dominant shielding mechanism, although some mistakenly defined the shielding mechanism based on the ratio of SEA over SER. Aside from the reflection as their dominant shielding mechanism, highly conductive electrospun shields are characterized by numerous internal interfaces that boost the internal scattering and thus shielding by absorption (Figure 2.7 (g)). In this case, a large portion of penetrated electromagnetic waves through the electrospun structures will be dissipated in the form of heat, resulting in higher SET and lower EM wave transmittance. Fiber-based nanomaterials or their nanocomposites can also be used to develop aerogels as lightweight EMI shields with exceptional SSE/t. Due to the presence of various internal interfaces, the internal scattering of EM waves inside aerogels is strong (Figure 2.7 (h)). Therefore, in the case of finite electrical conductivity, these structures tend to trap the penetrated EM waves and 44 transform their energy into heat 7, 77. The main shielding mechanism of aerogels depends on the type of materials and electrical conductivity of structures and should be defined based on the shielding coefficients. For instance, the aerogels of Ag nanowires/nanocellulose were characterized by R>0.5 and SER>3dB, resulting in a reflection-dominant shielding mechanism 78. However, a TiC/carbon hybrid aerogel derived from MXene/cellulose aerogel demonstrated an absorption-dominant behavior with SET=72.9 dB, SER=1.8 dB, and R=0.24 77. Multilayer fibrous EMI shields consist of various layers of conductive and magnetic materials or layers with various conductivities. The layers can be designed to generate a gradient of impedance mismatch, deemed as futuristic shields. In this approach, the interface between various layers can significantly boost the internal scattering and thus the shielding effectiveness of the structures (Figure 2.7 (i)). Despite the fact that the multilayer fibrous EMI shields are still in their infancy, developing EMI shields with alternating electrically conductive and magnetic layers using the electrospinning approaches can result in the emergence of novel classes of absorption-dominant EMI shields. Such an assembly of layers should be designed based on a careful selection of electrically conductive nanofillers and strong non-conductive magnetic nanoparticles, similar to the study by Amini et al. 55 for conventional multilayer structures. 45 Figure 2.7. The interaction mechanisms between EM waves and diverse structures including (a) laminated thin-film, (b) layer-by-layer stacked configuration, (c) porous structure, and (d) segregated structure, (e) schematic of scattering parameters in a vector network analyzer (VNA) sample holder, (f) the relationship between R and SER in EMI shielding measurements, (g) enhanced internal scattering in various fibrous EMI shields, including electrospun fibers/mats (Reprinted with permission from ref. 79, Copyright 2021 Elsevier), (h) fibrous aerogels (Reprinted with permission from ref. 77, Copyright 2022 Elsevier), and (i) layered fibrous structures (Adopted with permission from ref. 80, Copyright 2021 Wiley VCH). 2.3. Aerogel fabrication protocols Aerogels, as the lightest 3D porous macrostructure, were first manufactured by Kristler in 1931 81 and are known for their ultra-lightweight and large surface area 82. Aerogel is referred to as a gel in which the whole liquid content is replaced with gas or air without the collapse of the gel network, leading to a hierarchically porous framework 83. The remarkable characteristics of aerogels, including their low density, abundant porosities across scales, large surface area, low thermal 46 conductivity, and induction of a hierarchically porous electrically conductive structure, make them promising for a wide range of applications 65, 84, 85. Their potential capabilities transform aerogels into promising tools for applications involving EMI shielding, energy storage, sensors, thermal insulating materials, aerospace, and beyond, revolutionizing features of advanced technological products 65, 86-89. The common aerogel manufacturing approach involves the formation of a starting gel through the sol-gel process. In this case, sol is attributed to colloidal particles distributed within a liquid medium, the size of which could be in the range of 2-200 nm. The gel corresponds to an interconnected semi-solid arrangement that is stable throughout the liquid medium and shaped according to the container. The typical process starts from gel formation and aging to drying, resulting in an ultra-lightweight porous arrangement 89, 90. The liquid within the generated gels can be extracted through several drying methods, including ambient pressure drying, vacuum drying, supercritical drying, and freeze drying.89 The ambient pressure drying can take place when the cell walls are robust enough to withstand the capillary pressure, precluding the irreversible shrinkage of porous structures. Two main strategies have been considered for drying at ambient pressure: (i) employing a solvent exchange step using low surface tension solvents, such as ethanol, acetone, and hexane, to minimize capillary pressure, and (ii) enhancing the gel’s robustness to withstand the applied capillary stress. Supercritical drying is another drying approach that allows the preservation of the porous framework with the least shrinkage. This approach enables capillary force minimization and solvent removal within the pores of the gel under supercritical conditions. Supercritical-based drying approaches usually take place through two main strategies: i) the low-temperature supercritical drying that involves the replacement of the synthesis solvent with a lower-47 temperature solvent, e.g., CO2 at supercritical state (90 atm, 40 °C), and ii) high-temperature supercritical drying, employing the alcohol at supercritical state (120 atm, 265 °C) to dry the gel and obtain an aerogel. In the low-temperature state, this method has some limitations in water removal owing to the poor CO2 solubility in water at supercritical conditions, necessitating the replacement with an organic solvent.89 Freeze-drying is another widely used gel-drying approach, enabling aerogel production with the least shrinkage and excellent pore preservation. In this method, the drying process takes place at low temperatures and pressures to sublimate ice crystals instead of gas-liquid transformation.89 Both supercritical and freeze-drying are capable of preventing structure shrinkage as a result of capillary pressures caused by the outer surface menisci. This prevents the collapse of the cell walls and maintains the integrity of the 3D structured porous frameworks even at ultra-low densities.91-94 The formed porous constructs are named xerogel, cryogel, or aerogel, according to the drying method used. The term "xerogel" typically refers to materials dried at ambient pressure and temperature, resulting in a structure with higher density compared to cryogels and aerogels. In contrast, porous structures created through freeze-drying (lyophilization), which involves freezing the gel and sublimating the ice crystals, are known as "cryogels". When supercritical drying is used, the resulting porous structure is called an "aerogel".95, 96 Notably, the literature related to hierarchically porous constructs commonly uses the term "aerogels" for the majority of the resulting structures. Therefore, we adopt the term "aerogels" to align with the terminology used in published research. In cases where nanomaterials do not have the proper structuring capability, like the case of some metal-organic frameworks (MOFs) and/or some types of covalent organic frameworks (COFs), to yield free-standing aerogels with proper structural integrity, potent structuring components can be 48 used to address this weakness. In this case, hybridization of nanomaterials with less structuring capability with other compounds as integrity boosters or supporting scaffolds, e.g., graphene oxide 97, 98, cellulose 99-101, chitosan 102, 103, melamine 104, 105, and so on, can significantly increase the integrity of the final structure toward the demand of advanced applications. Figure 2.8 showcases a summary of the most common supporting scaffolds used in the preparation of aerogels. Figure 2.8. Potential supporting scaffolds to yield free-standing aerogels, including wood aerogel, carbon aerogel, chitosan-based aerogel, aramid nanofiber-based fibrous aerogels, melamine foams, polyacrylonitrile (PAN) fibrous aerogels, and cellulose aerogels. 49 The aerogels demonstrate exceptional potential for creating absorption-dominant shielding constructs, attributed to the formation of an electrically conductive, or potentially conductive-magnetic, network within a hierarchically porous structure designed to minimize surface reflections. This allows the EM waves to penetrate the aerogel porous medium and become highly dissipated as a result of multiple interfacial scattering combined with EM wave dissipating parameters like dielectric and magnetic losses 65. However, despite the potential of aerogels for EMI shielding 65, the inability of traditional fabrication methods to engineer the function and properties across dimensions, combined with the weak mechanical properties or structural integrity of some aerogels, limited their function toward real-world applications 89. Hence, alternative aerogel manufacturing roadmaps are needed to address the limitations of current technologies. To this end, interfacial complexation through nanoparticle jamming provides a great opportunity to address these challenges. This approach facilitates the engineering and precise control of aerogel features across multiple dimensions, allowing the customization of the hierarchically porous structure to incorporate desired properties on demand.4, 106 Given these promising potentials, we focus on the fabrication of soft materials and aerogels through interfacial science, with a particular emphasis on applications in electromagnetic interference (EMI) shielding. 2.3.1. Liquid-templated soft materials and aerogels Using structured liquids as a template for developing mechanically stable functional aerogels is a relatively new topic in the field of soft materials. However, we believe this approach holds promise as a groundbreaking fabrication platform with diverse potential applications. Firstly, the interfacially driven skin that stabilizes structured liquids plays a crucial role in maintaining the integrity of the resulting aerogels. Furthermore, this skin imparts specific chemical characteristics to the final constructs. These properties are determined by the type of ligands, nanoparticles, or 50 macromolecules incorporated into the original structured liquids, allowing for tailored functionality in the aerogels. For instance, the aerogels fabricated based on a liquid template that is stabilized by Ti3C2TX/POSS NPS showcased exceptional hydrophobic characteristics and water stability.40 It is worth noting that Ti3C2TX aerogels with numerous hydrophilic functional groups usually degrade in humid environments and cannot be submerged into aqueous media.107, 108 However, by utilizing interfacial complexation techniques, researchers were able to create a structure with POSS molecules uniformly distributed at the surface of MXene flakes. This arrangement endows the final aerogels with hydrophobic characteristics and exceptional water stability. Consequently, this development allows the aerogel to be submerged in an aqueous environment without concerns about its structural integrity, opening up new possibilities for its use in various water-related applications.40 In addition, structured liquids offer a powerful means to integrate the intrinsic properties of nanoparticles into final structures in a customizable way. For example, the creation of worm-like conductive aerogels using Ti3C2TX/GO takes advantage of the surfactant-like properties of GO.25 When coupled with a ligand, GO stabilizes liquid-like threads while incorporating Ti3C2TX imparts unique electrical conductivity to the structure, making it suitable for a variety of applications. Importantly, these aerogels do not require polymeric additives or crosslinkers, which typically increase the density of the final products significantly. In what follows, we will explore a few pioneering studies focused on the potential applications of liquid-templated aerogels. Our discussion will center on the inherent characteristics, including the chemistry of the interface and the controllable composition and porosities of these aerogels, which have led to breakthroughs in the field of soft functional materials. 51 2.3.2. Conductive liquid-templated aerogels for EMI shielding Liquid-templated aerogels made from 2D nanomaterials like MXene and reduced graphene oxide (rGO) have been used in EMI shielding applications because they combine high electrical conductivity, exceptionally low density, and high porosity in one package.25, 109 These aerogels can be engineered to achieve high absorption indices and excellent shielding effectiveness while maintaining low density and customizable thickness, making them versatile and cost-effective solutions for diverse EMI shielding applications.54, 110 Shi et al.40 were among the first researchers to utilize liquid-templated aerogels of MXenes for EMI shielding. In their study, they reported the co-assembly of Ti3C2Tx and POSS-NH2 at the toluene/water interface, which stabilized oil-in-water Pickering emulsions. These emulsion templates were then concentrated through simple centrifugation and used as a template to fabricate lightweight, hydrophobic, isotropic MXene aerogels with outstanding mechanical properties (Figure 2.9). These aerogels served as a framework for developing conductive epoxy nanocomposites; the MXene aerogels were impregnated with epoxy precursors and allowed to cure. The resulting polymer nanocomposites, with a very low MXene filler content (0.40 vol% of Ti3C2Tx), exhibited SET of 34.5 dB, significantly surpassing conventional polymer nanocomposites of MXene. However, the EMI shielding mechanism of these aerogels primarily relied on reflecting electromagnetic waves due to their relatively high electrical conductivity of 195.3 S/m, leading to a substantial impedance mismatch at the interface of these structures. More recently, worm-like aerogels of Ti3C2TX/GO were utilized to develop a new class of EMI shields.25, 111 This strategy focused on two key factors: 1) Keeping the electrical conductivity of these aerogels relatively low to allow incident electromagnetic waves to enter the structures with minimal reflectance. 2) Leveraging the dual micro-to-macro-scale porosities of worm-like 52 aerogels, unique to these structures, to enhance internal scattering and absorption capabilities. This approach enabled us to achieve high SET values (>30 dB) and absorption-dominant characteristics (A > 0.5) for some of these samples. For instance, using worm-like templates of Ti3C2TX/GO, ultra-lightweight aerogels with a density of 3-7 mg/cm3 were obtained. When these aerogels served as the backbone for epoxy nanocomposites, unique polymer nanocomposites with extremely low filler content (0.3-0.7 wt%) and exceptional EMI shielding characteristics (SET of 31.7–51.4 dB and A ≈52–54% were achieved, indicating dominant absorption behavior) for the samples.25 This highlights the potential of liquid-templated aerogels for large-scale and cost-effective fabrication of modern EMI shields for military and commercial purposes. Janus aerogels of Ti3C2Tx/GO:mGO/GO, with non-interfering magnetic/conductive domains, are also utilized for developing absorption-dominant aerogel traps, exhibiting impressive performance with a SET of approximately 51 dB, SER of around 0.4 dB, and A = 0.91.111 In this system, the inclusion of non-interfering magnetic/conductive domains in these aerogels further reduces reflectance, as the presence of magnetic stripes adjacent to conductive strips at the interface significantly further reduces the impedance mismatch. Moreover, the interface between magnetic and conductive domains within the aerogels contributes to internal scattering and enhances the absorption capability of these aerogels. These advantages, combined with the absence of thermal and chemical reduction requirements, position these Janus aerogels at the forefront of the EMI shielding field. 53 Figure 2.9. Schematic showing the fabrication of MXene-based structured Pickering emulsions that were used for developing aerogel-based EMI shields through the liquid templating approach. Reproduced with permission.40 Copyright 2019, Wiley-VCH. 54 Chapter 3: Nanomaterials Synthesis & Characterization This chapter reports detailed information on procured or synthesized 1D/2D nanomaterials as the basis of aerogel manufacturing. These nanomaterials include 2D nanoflakes like graphene oxide (GO) and magnetic graphene oxide (mGO) and 1D biopolymers like cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs). Accordingly, a comprehensive overview is provided, detailing the analytical chemical reagents used, the procedures followed, the characterization techniques employed, and the validation of the successful synthesis of the nanomaterials. 3.1. Materials In this thesis, active nanomaterials were synthesized using analytical-grade chemical reagents. For the synthesis of graphene oxide (GO), graphite flakes were supplied by Asbury Carbons; other reagents such as orto-phosphoric acid 85% (H3PO4), sulfuric acid 95-98% (H2SO4), potassium permanganate (KMnO4), hydrochloric acid 37% (HCl), hydrogen peroxide 30% (H2O2), and anhydrous ethanol (≤0.003% H2O) were supplied by Sigma-Aldrich. For the preparation of magnetic nanoparticles (Fe3O4), analytical grade iron (II) chloride tetrahydrate (FeCl2.4H2O), iron (III) chloride hexahydrate (FeCl3.6H2O), and ammonium hydroxide 28-30% (NH4OH) were used and supplied by Sigma-Aldrich. Throughout the production procedures, ultra-pure deionized water (18.2 MΩ) was utilized, generated via the ELGA model MEDICA EDI 15/30. For the fabrication of nano-fibrillated cellulose, i.e., cellulose nanofiber (CNF), required chemical regents, including sodium hydroxide (NaOH ˃97%), 2,2,6,6-Tetramethylpiperidine 1-oxyl, 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) (98%), sodium bromide (NaBr ≥99.5%), and sodium hypochlorite (NaCIO) solution (10-15 %) were supplied by Sigma-Aldrich. The refined and bleached Eucalyptus kraft pulp with a solid content of 2 wt% was considered the source of 55 CNF (dry weight: 30 g and wet weight: 1500 g). The cellulose nanocrystals (CNCs) were supplied by CelluForce and employed for aerogel manufacturing. 3.2. Nanomaterials Synthesis 3.2.1. Graphene oxide Well-exfoliated GO flakes were produced according to the improved Hummers’ method reported by Marcano et al. 112, with some improvements owing to the nature of used graphite flakes. Briefly, first, H2SO4 and H3PO4 were mixed with a ratio of 9:1 (360 mL:40 mL), followed by stirring for 10 min at 350 rpm. Next, 3 g of graphite flakes were added to the acidic mixture and stirred for 30 min at ambient temperature, followed by reducing the suspension temperature to 0-5 °C via an ice bath. After that, 18 g KMnO4 was slightly added to the suspension and then mixed for 30 min within the ice bath. The ice bath was replaced with a silicon oil bath, and the suspension temperature increased slightly to 50 °C with a very slight ramp. The resulting mixture was stirred for 16 h at 50 °C, cooled down after the considered time, and then terminated via a mixture of 800 mL deionized water and 5 mL H2O2. The exfoliated GO flakes were then purified through a stepwise protocol. The as-synthesized GO flakes were separated from the acidic medium through centrifugation at 11000 rpm and then washed several times with deionized water, 30 vol% HCl, and anhydrous ethanol till reaching the pH of 6. The purified GO suspension was thence diluted to the concentration of ~2 mg mL-1, followed by ultrasonication for 1 h at moderate power within an ultrasonic bath. The ultrasonicated and stabilized suspension was thence applied to centrifugation at 3500 rpm for 15 min to separate the well-exfoliated GO from few-layer GO and graphite oxide flakes. The collected supernatant as the main product was thence concentrated through centrifugation at 11000 rpm for 1 h to reach a concentration between 10-12 mg mL-1. The final concentrated GO suspension was kept in a sealed container till further use. 56 3.2.2. Magnetic graphene oxide Magnetic nanoparticles were synthesized according to the co-precipitation of FeCl2.4H2O and FeCl3.6H2O. For this matter, FeCl2.4H2O and FeCl3.6H2O were added with a molar ratio of 2:1 in 100 mL of deionized water and vigorously stirred at room temperature under the N2 atmosphere. Next, the ammonium hydroxide (28-30%) solution was added to the resulting mixture dropwise till reaching the pH of 9. The obtained mixture was thence stirred at 350 rpm with a temperature of 60 °C for 1 h until the magnetic (Fe3O4) nanoparticles formed. Afterward, the precipitated Fe3O4 nanoparticles were collected with a strong magnet and washed several times with ultrapure deionized water to wash off impurities. The obtained Fe3O4 nanoparticles were dried overnight at 60 °C and used for immobilization on the surface of GO. For loading the Fe3O4 nanoparticles on the surface of GO, first, 10 mL of the stock suspension of GO with concertation of 10 mg mL-1 was added to 25 mL of deionized water; meanwhile, 100 mg of Fe3O4 nanoparticles were ultrasonically mixed within 15 mL deionized water followed by subsequent stirring till gaining a fully homogeneous suspension. The GO suspension was placed under a probe sonicator, and the homogeneous Fe3O4 suspension was slightly added to it. Next, the suspension was stirred overnight at 50 °C till full immobilization of Fe3O4 nanoparticles on the surface of GO sheets. The obtained suspension contains 4 mg mL-1 decorated GO sheets with Fe3O4 nanoparticles (GO-Fe3O4). To get a higher GO-Fe3O4 concentration, the suspension was concentrated via ultrasonication at 11000 rpm for 1 h. 3.2.3. Cellulose nanofibers Herein, the TEMPO-mediated oxidation, followed by the mechanical treatment, is used to fabricate nano-fibrillated cellulose from commercial softwood bleached pulp. Accordingly, the cellulose 57 nanofiber (CNF) is prepared based on a stepwise procedure. In this matter, first, 460 g of refined, bleached Eucalyptus kraft pulp is dispersed within 23 L of deionized water (2 wt%) and mixed via a repulper two times. The refining process is performed via a valley beater until reaching the CSF of 350. Afterward, an aquatic mixture of processed pulp within deionized water with the concertation of 15 g dry pulp per Kg (1.5 wt%) was prepared. Next, 3.09 g NaBr and 0.48 g of ground TEMPO were dissolved within 300 mL of deionized water for 30 min. Meanwhile, 85.89 g of NaCIO (13%) solution is poured into a beaker, and the pH is adjusted to 10 using 3 M HCl. Afterward, the pulp suspension is poured into a large 4 L beaker and stirred at ambient temperature (25 °C) at 200 rpm. The aquatic mixture of NaBr and TEMPO was added to the pulp suspension and agitated for 3 min, followed by dropwise addition of NaCIO to the suspension and subsequent addition of deionized water till reaching a volume of 3 L (1 wt%). The pH of the suspension is adjusted at 10 ± 0.1 via 3M NaOH till no more decline in the pH is observed; this means that no more -COOH functional groups were created, and NaCIO is fully consumed within the process. The pH of the suspension declined to 7 via 3 M HCl; the resulting mixture was centrifuged at 8000 rpm for 5 min and washed with deionized water till the conductivity of the supernatant reached less than 5 µS cm-1. The obtained nano-fibrillated cellulose was thence stored at 3 °C till further consumption. The chief mechanism of such oxidation through the TEMPO-NaBr-NaCIO system is based on the regioselective conversion of the primary alcohols, viz., C6 hydroxyls within the cellulose chain, into carboxylic acid functional groups 113. Through the TEMPO-oxidation process, the cellulose fibrils that are strongly adhered to each other via hydroxyl (-OH) functional groups are converted into carboxylic acid-functionalized fibrils with distinctive electrostatic repulsion that facilitates their separation 114. 58 3.3. Characterizations The synthesized nanomaterials were characterized via diverse analyses. In this regard, the initial assessment of synthesized nanomaterials was conducted via Fourier-Transform Infrared Spectroscopy (FTIR) (Nicolet-S20) in the spectrum range of 600-4000 cm-1, and micro-Raman spectroscopy (Brucker Senterra II) assembled with an Olympus U-TV1X-2 microscope. The X-ray diffractogram of synthesized nanomaterials was collected via X-ray diffraction (XRD) setup (Brucker D8 Advance) with an Eiger2R 500K detector using a copper anode (K𝛼1=1.540 Å, K𝛼2=1.544 Å, and K𝛽1=1.392 Å) with a Ni K𝛽 filter. The height of the samples was manually determined via a twin laser system installed on the diffractometer. Moreover, the morphology and elemental composition of developed compounds were examined via a Field Emission Scanning Electron Microscope (FESEM) (Tescan Mira 3 XMU) equipped with an Oxford Instruments X-Max energy dispersive spectrometer (EDS) detector. Exfoliated GO flakes were examined via a High-Resolution Transmission Electron Microscope (HRTEM) (80-300 Titan LB) equipped with an aberration-corrector (CEOS), operated at 300 kV; images were also acquired using a FirstLight CCD, Gatan. 3.4. Nanomaterials Characterizations 3.4.1. Graphene oxide The synthesized nanomaterials were characterized via diverse analyses to confirm their successful synthesis with the required features and functionalities. In Figure 3.1 (a), the outcome of FTIR analysis for GO can be seen, demonstrating the fingerprint peaks of GO flakes synthesized via the improved Hummers methods 112. As illuminated, the appeared peaks in the FTIR spectrum of GO are attributed to the C-O (1090 cm-1), C-O-C (1227 cm-1), C-OH (1390 cm-1), C=C double bonds 59 carbon atoms (1630 cm-1), carbonyl (C=O) moieties (1740 cm-1), and hydroxyl (-OH) functional groups (3380 cm-1) 115, 116. Figure 3.1 (b) depicts the outcome of micro Raman spectroscopy for the GO flakes. As depicted, GO showed well-defined peaks at 1336 and 1579 cm-1, which is attributed to the D-band and G-band of GO flakes. The appeared peak at 2672 cm-1 corresponds to the 2D-band, showing the Raman signature of the sp2 graphitic compounds. The as-developed GO flakes also showed an ID/IG ratio of 0.87, revealing the controlled rate of defects and high quality of GO flakes 117, 118. Figure 3.1 (c) exhibits the X-ray diffractogram of GO. Based on the obtained diffractogram, GO demonstrated a well-defined sharp peak at 2θ of 11.1 attributed to the (001) crystalline plane of GO and confirmed the prosperous exfoliation of graphite flakes via the employed method 119, 120. Figure 3.1 (d-f) illustrates the FESEM images of GO flakes. According to Figure 3.1 (d & e), obtained GO flakes show a large active surface area with a 2D morphology. Likewise, Figure 3.1 (f) shows a view of the well-exfoliated GO flakes packed on each other, confirming the success of the employed methodology in the exfoliation of GO flakes. Following previous analyses, the HRTEM assessment of GO also exhibited the formation of 2D single-layer GO with a wide active surface area and large flakes (Figure 3.1 (g)). In addition, high magnification HRTEM assessment also confirms the formation of high-quality single atomic layer GO flakes with the least defects, which is in accord with the obtained data from micro Raman spectroscopy (Figure 3.1 (h)). The respective SEAD pattern of GO flakes also depicts the well-arranged crystalline structure of as-synthesized GO flakes (Figure 3.1 (i)). 60 Figure 3.1. The outcome of the characterization for exfoliated GO flakes; (a) FTIR spectrum of GO, (b) micro-Raman spectroscopy of GO, (c) X-ray diffractogram of GO, (d-f) FESEM images of well-exfoliated GO flakes, (g) HRTEM image of single atomic layer GO flake, (h) high magnification HRTEM image of GO, and (i) SEAD pattern of GO flakes. EDX analysis is performed to assess the elemental distribution of GO flakes. Figure 3.2 (a-c) demonstrates the EDX and EDX mapping of GO flakes. As shown, GO flakes consisted of 50.0 wt% oxygen, 43.7 wt% carbon, 5.6 wt% sulfur, 0.5 wt% nitrogen, and 0.3 wt% rest of the elements (Cl and P), homogeneously distributed throughout the 2D surface area of GO. 61 Figure 3.2. (a) FESEM image of the focus area for EDX assessment; the scale bar is equal to 100 µm. (b) EDX analysis of GO flakes along with the elemental distribution in wt%, (c) EDX mapping analysis of GO flakes. 3.4.2. Magnetic graphene oxide The successful immobilization of magnetic nanoparticles on the surface of GO was assessed through diverse analyses. Figure 3.3 depicts the X-ray diffractogram, micro Raman spectroscopy, and FESEM images of GO-Fe3O4 hybrid magnetic flakes. As depicted in part (a), the applied treatment and ultrasonic assembly of Fe3O4 on the wide active surface area of the GO flakes led to a shift in the 2Ѳ fingerprint peak of GO from 11.1 for neat GO to 7.97 for magnetic GO, corresponding to (001) crystalline plane of GO. This shift shows the change in the d-spacing of GO from 7.980 Å to 11.08 Å for magnetic GO and also the interaction of GO flakes with Fe3O4 nanoparticles. Additionally, the heat and/or ultrasonic treatment of GO flakes during Fe3O4 assembly reduced a portion of GO flakes into rGO, as evidenced by the 2Ѳ peak of 21.24 62 corresponding to the (002) plane of GO. Other appeared peaks at 2Ѳ positions of 18.34, 30.24, 35.64, 43.21, 53.53, 57.26, 62.90, and 74.46 are attributed to the (111), (220), (311), (400), (422), (511), (400), and (533) crystalline planes of Fe3O4 nanoparticles, which is in well-accord with the standard card of JCPDS 19-0629, showcasing the successful immobilization of magnetic nanoparticles on the surface of GO 121. Figure 3.3 (b) demonstrates the micro-Raman spectroscopy of magnetic GO. As illustrated, magnetic GO shows the two fingerprint peaks of GO at 1350 and 1587 cm-1, corresponding to the D-band and G-band of GO flakes. In this case, the ID/IG ratio was changed from 0.87 for GO to 0.95 for GO-Fe3O4, indicating the rise in the level of structural defects owing to the heat and/or ultrasonic treatment of GO that was also evidenced in the XRD analysis upon the appearance of the peak at 2Ѳ of 21.24 related to the reduced form of GO 119-122. Likewise, Figure 3.3 (c) and (d) demonstrate the FESEM images of magnetic GO flakes. As depicted, the employed procedure leads to the successful decoration of magnetic nanoparticles, i.e., Fe3O4, on GO and the formation of 2D magnetic flakes with homogenous distribution of magnetic nanoparticles throughout GO flakes' wide active surface area. These analyses confirm the prosperous formation of 2D magnetic flakes of GO with desired features toward interfacial assembly. 63 Figure 3.3. (a) X-ray diffractogram, (b) micro Raman spectroscopy, and (c & d) FESEM images of GO-Fe3O4 flakes; the scale bar corresponds to 20 µm. Figure 3.4 showcases the EDX and EDX mapping analyses of magnetic GO. As shown in this Figure, magnetic GO consists of 54.2 wt% iron, 27.1 wt% oxygen, 12.7 wt% carbon, 0.8 wt% sulfur, 2.3 wt% nitrogen, and 2.9 wt% chlorine. Importantly, magnetic iron nanoparticles were homogeneously distributed throughout the surface area of GO, leading to a homogenous magnetic response from the 2D magnetic flakes. 64 Figure 3.4. (a) FESEM image of the focus area for EDX assessment; the scale bar is equal to 10 µm. (b) EDX analysis of GO-Fe3O4 flakes along with the elemental distribution in wt%, (c) EDX mapping analysis of GO-Fe3O4 flakes. 3.4.3. Cellulose nanofibers Figure 3.5 demonstrates various analyses of CNF, including (a) FTIR, (b) X-ray diffractogram, and (c) AFM analyses. The FTIR analysis is performed to assess the chemical functionalities and the prosperous formation of TEMPO-oxidized CNF (TOCNF). As depicted in Figure 3.5 (a), the broad peak at about 3339.33 cm-1 is attributed to the stretching vibration of hydroxyl (-OH) functional groups. Accordingly, the presence of absorbed water molecules along with intra- and/or intermolecular hydrogen bonds could contribute to the broadness of the hydroxyl peak. Moreover, the peak at about 2883.71 cm-1 is attributed to the C-H stretching vibration. The major characteristic of TOCNF revealed itself at about 1603.96 cm-1, corresponding to the sodium-associated C=O stretching vibration of carboxyl functional groups. The other prominent peak of C-O arose from the symmetric stretching vibration of -COONa and appeared at about 1412.57 cm-65 1. Other peaks at about 1158.65 and 1022.65 cm-1 correspond to the C-O-C and C-O stretching vibrations within the CNF structure, respectively 123, 124. Figure 3.5 (b) illustrates the X-ray diffractogram of TOCNF; as depicted, CNF showed two well-defined 2Ѳ peaks at about 15.01 and 22.55 corresponding to the (110) and (200) crystalline planes of cellulose.125 In addition, the well-defined filamentous morphology of TOCNF was identified via the AFM analysis, as depicted in Figure 3.5 (c). The obtained outcomes vividly illuminated the successful formation of TOCNF with desired morphology, crystalline structure, and functionalities. Figure 3.5. Characterization of CNF including (a) FTIR, (b) X-ray diffractogram, and (c) AFM analyses. 66 Chapter 4: From Structured Liquid Templates to Filamentous Aerogels Modern materials science has witnessed the era of advanced fabrication methods to engineer functionality from the nano- to macro-scales. Versatile fabrication and additive manufacturing methods have been developed, but the ability to design a material for a given application is still limited. In this chapter, I introduce a novel strategy that enables target-oriented manufacturing of ultra-lightweight aerogels with on demand characteristics. The process relies on controllable liquid templating through interfacial complexation to generate tunable, stimuli-responsive 3D-structured (multi-phase) filamentous liquid templates. The methodology involves nano-scale chemistry and micro-scale assembly of nanoparticles (NPs) at liquid-liquid interfaces to produce hierarchical macroscopic aerogels featuring multi-scale porosity, ultra-low density (3.05-3.41 mg cm-3), and high compressibility (90%) combined with elastic resilience and instant shape recovery. I overcome the challenges facing ultra-lightweight aerogels, including poor mechanical integrity and the inability to form predefined 3D constructs with on demand functionality for a multitude of applications. In this chapter, I chiefly focused on the optimization of the process, designing a roadmap to engineer the features of the interfacially driven filamentous aerogels toward the demand for advanced applications. 4.1. Introduction The use of interactions at the interface between two immiscible liquids is an emergent strategy to assemble nanoparticles (NPs) in a constrained setting, spurring much academic interest, since it underpins many technological developments 9, 23, 42. The soft liquid-liquid interface provides an ideal platform to assemble chemically functionalized NPs into densely packed 2D arrays on planar and curved interfaces, which can be easily integrated into 3D meso- and macro-scale constructs 4, 67 40, 126, 127. Such a controllable approach allows the generation of hierarchical soft materials, where the inherent characteristics of NPs are integrated into the final assembly to impart unique electrical, magnetic, optical, and stimuli-responsive properties 4, 23. The interfacial interactions between functionalized NPs dispersed in one liquid and oligomeric/polymeric ligands with complementary functionality dissolved in a second immiscible liquid form so-called nanoparticles surfactants (NPSs) at the interface, markedly increasing the binding energy of the NPs to the interface 128-131. This process leads to the formation of robust NPS assemblies at the liquid-liquid interface between two immiscible liquids, eventually leading to a jamming of the interfacial assemblies. These jammed assemblies can support compressive loads, enabling the structuring of liquids. Interfacially jammed assemblies can be used to stabilize a jetted stream of one liquid into a second immiscible liquid, i.e., all-liquid 3D printing, by locking the liquids into non-equilibrium shapes 130, 132. The jamming of NPs at the interface, key to structuring the liquid constructs, results from the formation of a percolated pathway of NPSs capable of withstanding compressive loads imposed on the assembly 27, 133, 134. This cooperative assembly can be used to form multi-functional building blocks, allowing the development of the next generation of stimuli-responsive soft matter with applications ranging from all-liquid electronics to bicontinuous separations systems and biphasic reactors 9, 27, 135, 136. The key to liquid structuring is to overcome the applied pressure gradients on the liquid jet and resulting instabilities. According to the Plateau-Rayleigh instabilities, upon the injection of a falling liquid jet into another medium, beyond a given distance, the liquid jet will be accelerated and lengthened, leading to a decline in the jet’s radius, increasing the surface area of the jet relative to the volume. The instability leads to characteristic periodic oscillation in the jet diameter. The increase in the amplitude of these oscillations increases the curvature sites on the falling jet, viz., 68 causing concave and convex sites, giving rise to the pressure gradient and thus generating a flux momentum from high-pressure areas (concave areas) to low-pressure areas (convex areas). This induced flux from high- to low-pressure sites decreases the surface area, leading to an increase in Young-Laplace pressure gradients and interfacial tension, resulting in droplet formation to minimize the interfacial area of a droplet of a given volume 43, 44. The jammed jets of one liquid in another yield tubular or filamentous liquid constructs by injecting a stream of the liquid containing engineered NPs into the immiscible liquid phase containing active ligands 4, 7. The efficient generation of filamentous liquid constructs requires the formation, assembly, and jamming of NPSs that are more rapid than the flow of liquids to change shape to minimize the interfacial area. The solid-like layer of jammed NPSs encasing the tubular liquid thread preserves the integrity of the liquid construct 23, 27, 29. The filamentous liquid construct can be transformed into a 3D aerogel by removing the liquids via evaporation or lyophilization, where the resulting aerogel is self-supporting and porous on multiple length scales 7, 24. A multi-length scale porosity is advantageous for designing reconfigurable and engineerable aerogels for advanced applications, such as electromagnetic interference (EMI) shielding and human motion monitoring 7. There is still, though, a huge gap in the generation of robust filamentous liquid constructs with tailored compositions, since the required rapid interfacial assembly to reduce interfacial tension and suppress the Plateau-Rayleigh instabilities limits materials selection to achieve the desired responsiveness to selected stimuli 7, 24. Here, we addressed this by developing a process, termed “liquid templating”, where hydrophilic NPs, e.g., graphene oxide (GO), GO decorated with Fe3O4 (GO-Fe3O4), and cellulose nanofibers (CNFs), very rapidly assemble at the interfaces of two immiscible liquids, enabling the formation of filamentous liquid threads with an on demand 69 composition. This process allows the assembly of tailored NPs at the liquid-liquid interface and the stabilization of filamentous structures that constitute a template for stimuli-responsive 3D filamentous aerogels, enabling the engineering from the nano-scale chemistry to assemblies on the micro- and macro-scale. The hierarchical 3D multi-scale arrangement and robust interfacial skin of these aerogels allow the production of ultra-flexible soft constructs capable of withstanding 90% compressive strain combined with a very rapid shape recovery. The engineerable nature of the process allows for the easy tunning of the features of aerogels across scales to meet the demands of advanced applications. 4.2. Materials For the aerogel manufacturing, GO, mGO, and TEMPO-oxidized CNF were used; detailed information about the materials used for the synthesis of these nanomaterials was outlined in Chapter 3. Hydrazine hydrate 50-60% (N2H4) (supplied by Sigma-Aldrich) was utilized for the initial reduction of aerogels toward oil absorption application; the applicability of the aerogels toward oil absorption is outlined in Chapter 5. The microfluidic injection medium was prepared via a mixture of hexane (97%) and PSS-[3-(2-Aminoethyl)amino] propyl-heptaisobutyl substituted (POSS-NH2) as the ligand (supplied by Sigma-Aldrich). 4.3. Nanomaterials synthesis: The complete details of the synthesis and characterization of nanomaterials, including GO, mGO, and CNF, are thoroughly discussed in Chapter 3. 4.4. Aerogels manufacturing protocol: The multifunctional aerogels with a well-defined 3D morphology were prepared upon freezing and lyophilization, i.e., freeze-drying, of a custom filamentous liquid template, prepared through 70 streaming an aqueous ink into an immiscible liquid host containing active ligands, viz., POSS-NH2. Accordingly, a mixture of hexane containing 1 mg mL-1 POSS-NH2 was prepared as the microfluidic injection medium and isolated till further use. For preparing the aquatic inks, aquatic mixtures of GO, 1:1 GO:GO-Fe3O4 (GO-Fe), and 1:1 GO:CNF (GO-CNF) with a final concentration of 10 mg mL-1 were prepared; detailed preparation parameters and composition/concentration of each aquatic ink can be seen in Table 4.1. Additionally, different ink concentrations (1, 3, 5, and 10 mg mL-1) were also prepared and used for various kinds of supporting experiments. Correspondingly, the prepared mixture of each ink was stirred for 3 h (400 rpm at 25 °C), followed by 30 min subsequent bath sonication at low power levels. Each prepared ink was placed within a syringe equipped with the desired needle gauge and assembled within the Allevi 2 3D bioprinter. A premixed injection medium of hexane-POSS-NH2 was poured into considered containers, and the needle was immersed within the printing medium. The aquatic ink was streamed within the hexane-POSS at a pressure between 8-15 psi till the required aerogel thickness was reached. The formed worm-shaped streams of aquatic ink within the hexane-POSS-NH2 were then transferred to an ultra-freezer and kept at -80 °C for 24 h. The hexane-POSS-NH2 was thence decent away, and the frozen samples were freeze-dried (LABCONCO 4.5 L, -50 °C benchtop freeze dryer) for 48 h. For the density measurement, after placing the frozen filamentous aerogel in the ultra-freezer, the filaments were washed several times with pure hexane to remove any impurities prior to the freeze-drying process. Five different samples of each type of aerogel were prepared, and their density was analyzed before and after thermal reduction. Additionally, for aerogels’ shrinkage measurements, three different samples were prepared with 10 mg mL-1 aqueous GO ink using gauge 18 (outer 71 diameter (O.D.) of 1.27 mm) needles during injection, and the average volume shrinkage and density were measured after thermal annealing at 800 °C under Ar for 1 h. For assessing the micro-scale pore size distribution, aqueous GO suspensions with concentrations 1, 3, 5, and 10 mg mL-1 were prepared and poured into different molds. The molds were thence placed in an ultra-freezer at -85 °C, and the frozen GO suspensions were lyophilized for 48 h to yield porous GO aerogel frameworks. The aerogels were thence analyzed via FESEM at different magnifications, and the pore sizes were measured using Image J software. The macro-scale porosity assessment was carried out by injecting the 10 mg mL-1 aqueous GO ink into a hexane domain containing 1 mg mL-1 POSS-NH2 using needles with different gauges (27 (O.D. of 0.42 mm) and 15 (O.D. 1.65 mm)). Accordingly, GO liquid templates were generated by injecting 2 mL of a 10 mg mL-1 stock GO suspension into a hexane-POSS-NH2 medium, and then the increase in the volume of the liquid template was monitored by considering the change in the needle gauge from 27 to 15. The generated liquid templates fabricated with needles with different gauges were used to yield free-standing aerogels, and the average filament diameter was assessed by processing FESEM images using Image J software. To measure the thickness of the skin around aerogel filaments, three different aerogel samples generated via 10 mg mL-1 GO ink were prepared and cut into two pieces using a sharp cutter. The aerogels cross-section was thence scanned via FESEM images, and the skin thickness of each sample was analyzed via Image J software. For micro-scale pore size, diameter, and skin thickness assessments, 50 different sites of each sample were analyzed, and the respective average values were reported. In all of the experiments and illustrated experimental graphs, the standard deviations were measured and reported. 72 Table 4.1. Composition and processing conditions of each aquatic ink. Aerogel Components & Ratios Concentration (mg mL-1) Stirring Bath Sonication Temperature (°C) GO GO, 1:0 1-10 3 h-400 rpm 30 min-low power 25 GO-Fe GO:GO-Fe3O4, 1:1 10 3 h-400 rpm 30 min-low power 25 GO-CNF GO:CNF, 1:1 10 3 h-400 rpm 30 min-low power 25 For the reduction or carbonization of GO, GO-Fe, and GO-CNF aerogels for shielding applications, aerogel samples were placed within an Across International tube furnace and thermally treated at 800 °C for 1 h under Ar atmosphere with a flow rate of 50 mL min -1. For oil absorption tests, GO aerogels were initially placed within a 3 MPa autoclave containing 10 mL 50-60% hydrazine hydrate, followed by treatment at 100 °C for 24 h. The initially reduced aerogels were then treated at 800 °C for 1 h under an Ar atmosphere to minimize the density and boost the multi-scale porosity of aerogels. 4.5. Characterization The developed graphene-based aerogels were characterized via diverse analyses. In this regard, the initial assessment of aerogels was conducted via Fourier-Transform Infrared Spectroscopy (FTIR) (Nicolet-S20) in the spectrum range of 600-4000 cm-1, and micro Raman spectroscopy (Brucker Senterra II) assembled with an Olympus U-TV1X-2 microscope. The Bruker D8 Advance X-ray diffractogram was used to characterize the materials. The instrument is equipped with an Eiger2R 500K detector, using a copper anode with K𝛼1=1.540 Å, K𝛼2=1.544 Å, K𝛼ave=1.5418, and K𝛽=1.392 Å. For samples examined with standard beam optic, a Ni K𝛽 filter was used, while for examined aerogel with parallel beam technique, a Göbel mirror was used. Sample position and height were manually optimized via a twin laser system assembled on the X-ray diffractometer. Of note, the parallel beam setup was used for assessing the aerogel samples owing to the inability of standard beam optics to properly examine the aerogels because of their 73 uneven surface and abundant porosities. The height of the samples was manually determined via a twin laser system installed on the diffractometer. Moreover, the morphology and elemental composition of developed aerogels were examined via a Field Emission Scanning Electron Microscope (FESEM) (Tescan Mira 3 XMU) equipped with an Oxford Instruments X-Max energy dispersive spectrometer (EDS) detector. The electrical conductivity of the reduced/carbonized aerogel samples was assessed through the Loresta GP resistivity meter (Mitsubishi Chemical Co. model MCP-T700). The dynamic interfacial tension (IFT) tests of developed inks were acquired by holding 5 µL of aquatic droplets of inks’ suspensions at the required concentration/composition in the organic hexane domain with and without POSS-NH2. The contraction/expansion test was also performed via injecting and withdrawing the droplet from the non-polar medium (hexane) with and without POSS-NH2 to analyze the wrinkles on the droplet and assess the jamming of nanoparticles. The water contact angle of double-step reduced GO aerogels was assessed through a goniometer (Rame´-hart Model 260) and the sessile drop method. The static contact angle of the aerogels was observed by depositing a 10 µL water droplet onto the surface through a microsyringe. The cyclic compression test was conducted using a universal tensile machine (Zwick/Roell) equipped with a 200 N load cell at 20, 40, 60, 70, 80, and 90% compressive strains with a loading/unloading speed of 5 mm/min. 4.6. Results and discussion Figure 4.1 shows the different stages of “liquid templating:” i) formation of the liquid template upon electrostatic interaction between ligand and nanoparticles (NPs) (Phase I); ii) freezing of the liquid template (Phase II); and iii) lyophilization of the liquid template to form an aerogel with a porous core surrounded by a solid skin (Phase III). Upon pressure-adjusted jetting of the aqueous 74 phase containing NPs into hexane containing POSS-NH2, initially, the POSS-NH2 rapidly assembles at the interface, forming a positively-charged POSS-NH3+ layer that reduces the interfacial energy and suppresses Plateau-Rayleigh instabilities. Subsequently, the GO flakes diffuse to and assemble at the interface, and then the deprotonated carboxylic acid (-COO-) groups of GO electrostatically interact with the protonated amine groups (-NH3+) of POSS-NH3+ 4. This electrostatic interaction between the ligand and NPs forms an assembly of nanoparticle surfactants (NPSs). The driving force of this pH-dependant electrostatic interaction stems from the pKa value of amine (~9) and carboxylic acid (~4.2) functional groups, allowing their protonation and deprotonation when the pKa value becomes higher and lower than the pH of the medium, respectively. This produces robust electrostatic interactions, leading to a cooperative interfacial complexation between the ligand and NPs, generating disordered assemblies at the interface, further reducing the interfacial energy, and leading to a skin around the filament 4, 22, 23. The selection of POSS-NH2 as a ligand for this process is advantageous because of its high interfacial activity and rapid diffusion to the interface, enabling the formation of NPSs. This process forms a robust interfacial skin at the interface of two immiscible liquids, preserving the integrity of filamentous liquid templates 7, 40. Freezing and lyophilizing the liquid templates lead to the formation of engineerable filamentous aerogels consisting of core-shell filaments composed of a robust solid skin wrapped around a porous tubular core. 75 Figure 4.1. Schematic illustration of the liquid templating methodology. (a) The developed process for generating hierarchical 3D aerogels with desired components and functionality, starting from injecting aqueous phase containing GO into an immiscible liquid, i.e., hexane, containing POSS-NH2 (Phase I) to freezing of liquid template (Phase II) and subsequent lyophilization to generate filamentous aerogels (Phase III). The aerogels comprise core-shell filaments with a thin solid skin wrapped around a porous core. In Phase I, * showcases the injection of aqueous GO-based inks into the hexane domain containing POSS-NH2, and ** indicates the interfacial complexation, viz., electrostatic interaction of ligands and NPs. As illustrated in Part II, the placement of the aqueous liquid template into a freezer at -85 °C leads to its freezing, whereas the hexane domain remains liquid owing to its low freezing point (-95.3 °C), enabling its separation before lyophilization. (b) Electrostatic interaction of POSS-NH2 molecule with GO through carboxylic acid deprotonation and amine functional group protonation. (c) (I) Break up of the liquid stream into discrete droplets to suppress instabilities, and (II) enhanced integrity of the liquid stream upon formation of NPSs at the interface, locking in the non-equilibrium shape of the liquid construct in the form of the filament. (d) The shape of the droplet in pendant drop tensiometry (I) in equilibrium without the presence of POSS in the oil phase and (II) in non-equilibrium shape upon the formation of a solid skin around the droplet as a result NPSs jamming, holding the integrity of liquid construct; the black dots in the image represent the GO dispersed in the aqueous phase. 76 A 3D printer is used for microfluidic injection of aqueous inks containing tailored NPs, i.e., GO (10 mg mL-1), GO:GO-Fe3O4 (1:1 (weight ratio), 10 mg mL-1), and GO:CNF (1:1, 10 mg mL-1), (Figure 4.2 (a)) into a PSS-[3-(2-aminoethyl)amino]propyl-heptaisobutyl substituted (POSS-NH2) solution in hexane. Initially, POSS-NH2 assembles at the interface between the two immiscible liquids, reducing the interfacial tension. The engineered NPs dispersed in the aqueous phase then diffuse into the interface and electrostatically bond to the POSS-NH2, forming NPSs that jam at the interface. This leads to the formation of a solid-like layer around the tubular liquid thread, locking-in the non-equilibrium shape of tubular filamentous liquid threads. The attachment rate depends on the NPs concentration and their diffusion coefficient in the aqueous phase 19, 137. The liquid phase is then rapidly frozen (Figure 4.2 (a) - part I) and lyophilized to yield 3D filamentous ultra-lightweight aerogels with the characteristics of the assembled NPs (Figure 4.2 (a) - part II). This methodology allows the generation of on demand 3D structured aerogels with controllable functionality and porosity (from micro-scale to macro-scale) by tuning the concentration/type of NPs, injection medium, injection parameters, and needle size. Figure 4.2 (b) shows schematics of the hierarchical 3D filamentous aerogel composed of GO (GO aerogel) (I), GO:GO-Fe3O4 (GO-Fe aerogel) (II-III), and GO:CNF (GO-CNF aerogel) (IV), where the shape or 3D architecture, diameter of the tubular filaments, composition and concentration of the substances, conductive and/or magnetic characteristics, and the stimuli responsiveness of these aerogels can be engineered by varying the chemical composition of constituent NPs and the ligands. As a direct consequence of reducing interfacial area and the associated compressive forces to the tubular liquid construct, generating stable jets of water in oil, e.g., hexane, and reaching the on demand characteristics in liquid templating require precise nano-scale engineering of the chemistry of the GO, GO-Fe3O4, and CNF with predefined features. As evidenced by Chapter 3, the GO 77 flakes have inherent functionalities, i.e., active carboxylic acid functional groups, that undergo electrostatic interactions with the ligands and form a robust skin around the liquid thread, enabling the liquid templating of aqueous inks containing hydrophilic nano-scale engineered GO-Fe3O4 and CNF NPs. The strong interfacial activity of GO enables the generation of filamentous liquid templates from GO (Figure 4.2 (c) (I)), GO:GO-Fe3O4 (Figure 4.2 (c) (II & III)), and GO:CNF (Figure 4.2 (c) (IV)) inks, leading to the formation of free-standing tailorable liquid templates of GO, GO:GO-Fe3O4 and GO:CNF (Figure 4.2 (d-f)). Notably, the magnetic liquid jets were responsive to an external magnetic field upon incorporating magnetic GO-Fe3O4 flakes into the inks (Figure 4.2 (c) part (III)). Different compositions of the interfacially active nano-scale materials can be used to generate custom liquid templates, demonstrating their versatility in varying the properties of the aerogels. The strong interfacial activity of GO accounts for the integrity of these liquid constructs, resulting from the co-assembly of nanosheets and POSS-NH2, forming a strong interfacial NPS skin, completely suppressing the break-up of liquid streams into discrete droplets. This was validated by dynamic interfacial tension (IFT) measured by pendant drop tensiometry (Figure 4.2 (g) and Figure 4.3). Upon injection of an aqueous ink containing 1 and 10 mg mL-1 GO into the non-polar hexane domain, the IFT rapidly decreased from ~49 mN/m (for neat water and hexane) to 27.28 and 6.56 mN/m, respectively, demonstrating the surfactant nature of GO and the influence of GO concentration on minimizing the interfacial tension 138. This surfactant-like character of GO arises from its dual hydrophilic-hydrophobic nature, having a non-polar basal plane and polar functional groups 7. However, even with this high interfacial activity, liquid-like GO aqueous suspensions are unable to form filaments in the absence of ligands in the non-polar domain, forming matrix-dispersed emulsions 24. By injecting the GO ink with concentrations of 1 and 10 mg mL-1 into the 78 non-polar hexane domain containing 1 mg mL-1 POSS-NH2, the GO rapidly migrated to the interface and tightly bonded to the ligands, thereby forming NPSs, lowering the IFT to 2.83 and 1.35 mN/m, leading to a robust solid-like tubular NPSs skin wrapping the aqueous thread. This interfacial skin can lock in the non-equilibrium filamentous shape of the jetted liquid by suppressing the Plateau-Rayleigh instabilities, preventing the break-up of the aqueous jet into discrete droplets 43. Mixtures of GO along with GO-Fe3O4 and CNF showed an equilibrium IFT of 1.05 and 1.60 mN/m (Figure 4.3 (h) and Figure 4.4), respectively, allowing liquid templating of the hybrid inks upon generation of a GO-based robust interfacial skin around the liquid threads. The beauty of the dual nature of GO is its ability to generate a robust interfacial skin and sustain the integrity of the liquid construct even in the presence of highly hydrophilic NPs (i.e., CNF and GO-Fe3O4) in the aqueous phase. This feature paves the way for designing on demand functionalities. The formation of the NPSs interfacial skin around the aqueous phase is visualized during the contraction/expansion of the pendent droplet in the non-polar hexane/POSS-NH2 domain (Figure 4.2 (i) and Figures 4.5-4.7). As shown, a droplet of 1 mg mL-1 aqueous GO suspension is suspended within the non-polar hexane medium containing 1 mg mL-1 POSS-NH2. Upon decreasing the volume of the droplet, the interfacial area decreases, and a compressive force is imposed on the assembly at the interface. This causes a wrinkling of the assembly, demonstrating the elastic nature of the interfacial skin. The wrinkles formation implies the secure positioning of GO by POSS-NH2 at the interface, generating a resilient interfacial thin film as a consequence of overlapping complex assemblies of GO-POSS-NH2 NPSs. This process leads to the formation of well-arranged 3D filamentous liquid constructs that can be used as a template for aerogel generation. Interestingly, the versatile nature of the process allows liquid templating in various non-polar solvents. Control 79 experiments show the possibility of stable liquid templating in low freezing point solvents, such as pentane and toluene, capable of being transformed into well-defined aerogels upon freezing and lyophilization (Figure 4.8). Figure 4.2. (a) Schematic illustration of 3D aerogels formation, showcasing (I) the freezing of the liquid template and (II) formation of aerogel after lyophilization, (b) production of aerogels with different compositions and characteristics, including (I) GO aerogel, (II) GO-Fe aerogel, and (III) GO-CNF aerogel; in this image, the brownish flakes in part (II) represent the GO-Fe3O4 flakes and the fibers on the aerogel in part (III) denote CNF. (c) Microfluidic injection of different aqueous inks, including (I) GO ink, (II & III) GO:GO-Fe3O4 ink, and (IV) GO:CNF ink into the non-polar hexane domain containing 1 mg mL-1 POSS-NH2; the concentrations of all inks were set at 10 mg mL-1. Formation of 3D liquid constructs out of (d) GO ink, (e) GO:GO-Fe3O4 ink, and (f) GO:CNF ink. Scale bars are equal to (c) (I) ~14.1 mm, (II) ~13.9 mm, (III) ~14.7 mm, and (IV) ~13.9 mm, (d) (I) ~12.3 mm, (II) ~3.8 mm, (e) (I) ~12.9, (II) ~6.8 mm, (f) (I) ~12.2 mm, and (II) ~6.1 mm. Of note, the showcased images in parts (c-f) were taken by a digital camera, and their scale bars are approximate. (g) Interfacial characteristics of different concentrations of aqueous GO suspension in non-polar hexane domain with and without POSS-NH2 (1 mg mL-1). (h) Interfacial tension of different aqueous inks containing GO, GO:CNF, and GO:GO-Fe3O4, with an initial concentration of 10 mg mL-1 in the hexane domain containing 1 mg mL-1 POSS-NH2. (i) Contraction and expansion assays of 1 mg mL-1 aqueous GO suspension within the hexane-POSS-NH2 medium; the wrinkles formed on the droplets imply the formation of elastic assemblies at the interface, i.e., interfacial complexation, as a result of NPs jamming. 80 Figure 4.3. Dynamic interfacial tension of aqueous GO suspensions in hexane (a) at 1 mg mL-1 concentration without POSS-NH2, (b) at 1 mg mL-1 concentration with POSS-NH2, (c) at 10 mg mL-1 concentration without POSS-NH2, and (d) at 10 mg mL-1 concentration with POSS-NH2. As evidenced, an increase in the concentration of GO in the presence of POSS-NH2 remarkably minimized the interfacial tension, paving the way for stable liquid templating. Figure 4.4. Dynamic interfacial tension of aqueous hybrid inks containing equal weight ratio (1:1) of (a) GO:CNF, and (b) GO:GO-Fe3O4 at the fixed concentration of 10 mg mL-1 against hexane-POSS-NH2 medium. 81 Figure 4.5. The contraction of the pendent drop of 10 mg mL-1 aqueous GO suspension in hexane containing 1 mg mL-1 POSS-NH2. Figure 4.6. The contraction of the pendent drop of 10 mg mL-1 aqueous GO:GO-Fe3O4 suspension in hexane containing 1 mg mL-1 POSS-NH2. Figure 4.7. The contraction of the pendent drop of 10 mg mL-1 aqueous GO:CNF suspension in hexane containing 1 mg mL-1 POSS-NH2. 82 Figure 4.8. (a) Liquid templating of 5 mg mL-1 aqueous GO suspension in different solvents, including pentane, toluene, and hexane containing 1 mg mL-1 POSS-NH2; the scale bar is equal to ~15.2 mm. Formation of stable 3D-structured filamentous GO liquid templates in (b) pentane, (c) toluene, and (d) hexane; scale bars are equal to (b) ~3.5 mm, (c) ~4.2 mm, and (d) ~3.7 mm. Generation of free-standing 3D-structured aerogels upon freezing and lyophilization of formed liquid templates in (e) pentane, (f) toluene, and (g) hexane; scale bars are equal to (e) ~4.8 mm, (f) ~6.9 mm, and (g) ~4.9 mm; of note, the images were acquired by digital camera and the scale bars are approximate. 83 Freezing and lyophilizing the structured liquid templates containing the engineered NPs led to the generation of well-arranged ultra-lightweight aerogels with a 3D hierarchical architecture, featuring a unique worm-like morphology with multi-scale porosity (Figure 4.9). These structures are among the lightest reported structures in the literature, and the very light hairs of a cactus can withstand their weight (Figure 4.9 (a)). The post-processing of these aerogels through thermal reduction at 800 °C under argon for 1 h (Figure 4.9 (b), the black sample) resulted in aerogel constructs with inherent electrical conductivity (Figure 4.9 (c)) or stimuli-responsive aerogels with a combined magnetic response and high electrical conductivity (Figure 4.9 (d)). The magnetic aerogels rapidly respond to an external magnetic field while maintaining their integrity. Additionally, for shrinkage assessment, a series of raw GO aerogel was prepared using a 10 mg mL-1 GO ink and injected with a needle gauge of 18 (outer diameter (O.D.) of 1.27 mm). The thermal annealing of the as-prepared GO aerogels at 800 °C in Ar for 1 h leads to an average volume shrinkage rate of 16.60% and a density of about 3.17 mg cm-3 after the reduction process. Morphological assessment of 3D structured filamentous aerogels prepared with GO, GO:GO-Fe3O4, and GO:CNF inks is shown in Figure 4.9 (e-j). As seen in the FESEM images, the lyophilization of the frozen templated structured liquids led to the formation of 3D filamentous aerogels with abundant controllable macro-scale porosities between filaments. Such a process enables controlling the 3D shape, morphology, size/dimension, and micro-scale/macro-scale porosity of aerogels by adjusting the liquid template for potential applications. 84 Figure 4.9. (a) Non-reduced and reduced GO aerogels on the very light hairs of cactus, (b) a view of the reduced and non-reduced aerogels and a comparison of their size after the thermal annealing at 800 °C under Ar for 1 h, (c) a view of lightweight reduced GO aerogel capable of conducting the electricity to light up an LED, (d) combined electrical conductivity and magnetic response in reduced magnetic GO aerogel. FESEM images of (I) aerogels and (II) zoom in within their filaments, including (e) non-reduced GO aerogel, (f) reduced GO aerogel, (g) non-reduced GO-Fe aerogel, (h) reduced GO-Fe aerogel, (i) non-reduced GO-CNF aerogel, and (j) reduced GO-CNF aerogel. Scale bars are equal to (a) ~9.5 mm, (b) ~10.8 mm, (c) ~11.0 mm, (d) ~9.7 mm, (e-j) (I) 2 mm, and (II) 500 µm; the reported values of scale bars in parts (a) to (d) are approximate. The developed aerogels were assessed via FTIR, micro-Raman spectroscopy, and parallel beam X-ray diffraction, showing the formation of a well-established complex between the ligand, i.e., POSS-NH2, and synthesized NPs. Accordingly, the developed aerogels with either GO, CNF, GO-Fe3O4, or a combination thereof were assessed before and after either hydrazine vapor treatment or thermal reduction at 800 °C under Ar for 1 h. Figure 4.10 depicts the FTIR spectrums of developed aerogels before and after thermal reduction. As depicted, the FTIR spectrum of non-reduced GO aerogel (Figure 4.10 (a)) shows well-defined peaks originating from the tight bond between the GO and POSS-NH2, leading to the formation of the so-called “nanoparticle surfactant (NPS)” during liquid template generation. In this spectrum, peaks at 738.60 and 835.99 cm-1 are attributed to the Si-C-H and Si-C stretching vibrations of POSS-NH2, respectively 139-141. One of 85 the main fingerprint peaks of POSS-NH2 appeared at 1099.22 cm-1, attributed to the Si-O-Si stretching vibration of siloxane groups, which are known as the prominent characteristic peak for the absorption of silsesquioxane cages 139, 142. Moreover, the peak at 1230.36 cm-1 and group peaks between 1330.64 to 1402.95 cm-1 are attributed to the stretching vibration of Si-C and bending vibration of -CH2CH2CH2- groups of POSS-NH2 skeleton, respectively 142, 143. Interestingly, the formation of NPS, owing to the bond between GO and POSS-NH2, leads to the formation of a hybrid structure that showed the main fingerprint peaks of GO in the FTIR spectrum. As illustrated, the peak at about 1465.63 cm-1, with a slight shift compared with neat GO, could be due to the C-OH group of GO. The broadened peaks at 1628.59 and 1740.44 cm-1 arise because of the merged C=C and C=O stretching vibration of GO and POSS-NH2 120, 122, 142. Importantly, the shift in these peaks compared with their original locations in the FTIR spectrums of GO and POSS-NH2 reveals the participation of oxygen molecules of amide functional groups in the complexation. Additionally, the group peaks between the range of 2867.63 to 2955.37 cm-1 are attributed to the stretching vibration of C-H functional groups originating from the six pendant organic arms of POSS 142. Moreover, the reduction of GO through thermal treatment at 800 °C under Ar leads to the removal of oxygen-based functional groups and considerable decline/removal of assigned peaks to the POSS-NH2 (Figure 4.10 (b)). As demonstrated, the main peaks at about 739.56, 802.24, 1122, and 2886.94-2979 cm-1 are attributed to the Si-C-H, Si-C, reduced Si-O-Si groups, and C-H stretching vibration, respectively. In addition, the FTIR spectrum of non-reduced GO-Fe aerogel (Figure 4.10 (c)) also depicted the formation of a hybrid complex among GO, POSS, and GO-Fe3O4. As depicted in Figure 4.10 (c), some main fingerprint peaks of POSS-NH2, including the stretching vibration of Si-C-H, Si-C, Si-86 O-Si, and Si-C, appeared at 739.56, 836.95, 1103.08, and 1230.36 cm-1, respectively. Other fingerprint peaks of POSS-NH2, including the bending vibrations of -CH2CH2CH2- and stretching vibration of C-H groups of organic pendant arms of POSS-NH2, appeared between ranges 1336-1435 cm-1 and 2870-2980 cm-1, respectively. The -OH groups of GO flakes showed themselves at about 1462.74 cm-1. Notably, owing to the assembly of different compounds through the formation of NPSs, both C=C and C=O functional groups showed several sub-peaks near each other. Accordingly, C=C double bonds appeared at 1644.98 and 1625 cm-1, while the C=O stretching vibrations appeared at 1715.37, 1731.76, and 1747.19 cm-1. The weak peak of hydroxyl functional groups was also observed at 3404.70 cm-1. Interestingly, hydrazine reduction of GO-Fe aerogel significantly declined the oxygen-based functional groups, increased the ratio of C=C double bond over oxygen-based domains, and maintained the POSS-NH2 skeleton wrapped around the filamentous threads (Figure 4.10 (d)). As demonstrated in Figure 4.10 (d), the hydrazine reduction of GO-Fe aerogel showcased all of the fingerprint peaks of POSS-NH2 with high intensity, including 742.45 cm-1 (Si-C-H), 836.95 cm-1 (Si-C), 1102.11 cm-1 (Si-O-Si), 1227.46 cm-1 (Si-C), 1367.28-1435.74 cm-1 (bending vibration of -CH2CH2CH2-), and 2871.48-2979.48 cm-1 (C-H stretching vibration). Meanwhile, this FTIR spectrum showcased elevated peaks of C=C double bonds carbon atoms at 1575.55 and 1666.91 cm-1 and also a considerable decline in the intensity of oxygen-based functional groups such as C=O stretching vibration (1752.01 cm-1), -OH stretching vibration of GO (1461.77 cm-1), and also hydroxyl functional groups, viz., -OH, (3198 cm-1). Although the reduction at high temperatures could change the nature of the wrapped shell around the filamentous threads through the carbonization and/or reduction process, the hydrazine reduction approach keeps the main skeleton 87 of the POSS-NH2 within the structure while it declines the content of the oxygen-based functional groups through the vaporized reduction process. Furthermore, the non-reduced GO-CNF aerogel (Figure 4.10 (e)) exhibits the main fingerprint peaks of GO, POSS-NH2, and CNF, showcasing the formation of a complex among the mentioned compounds. Accordingly, this FTIR spectrum showed stretching vibration of Si-C-H, Si-C, Si-O-Si, and Si-C at 738.60, 836.95, 1100.19, and 1230.36 cm-1, respectively, showing the presence of POSS-NH2 in the complex. The other peak at 1060 cm-1, along with the main fingerprint peak of POSS-NH2, originated from the C-O stretching vibration of CNF. Additionally, the related peaks of bending vibration of -CH2CH2CH2- groups of POSS-NH2 skeleton showed themselves between the range 1335.46-1382.71 cm-1, whereas the C-H stretching vibrations of POSS-NH2 appeared between 2886.91-2980.44 cm-1. Moreover, the secondary C-O stretching vibration of the CNF structure appeared at 1418 cm-1. The -OH stretching vibration of GO also showed itself at 1459.84 cm-1. Notably, most of the interactions between functional groups of GO, POSS-NH2, and CNF were observed between 1600-1750 cm-1, showcasing the residue of C=C and/or C=O functional groups of components participated in the interfacial complexation, confirming the interaction between the compounds mentioned above during the formation of NPS. The broad peak at about 3403.74 cm-1 originated from the hydroxyl (-OH) functional groups. The thermal reduction of GO-CNF aerogel also demonstrated the same outcomes as reduced GO aerogel, showing the removal of oxygen-based functional groups and the main skeleton of the POSS owing to the treatment at high temperatures. 88 Figure 4.10. FTIR spectrum of developed aerogels including (a) non-reduced GO aerogel, (b) reduced GO aerogel, (c) non-reduced GO-Fe aerogel, (d) reduced GO-Fe aerogel, (e) non-reduced GO-CNF aerogel, and (f) reduced GO-CNF aerogel. 89 Figure 4.11 depicts the outcome of micro Raman spectroscopy for reduced and non-reduced aerogels developed based on either GO, CNF, GO-Fe3O4, or a combination thereof. As demonstrated, all aerogels exhibited two well-defined peaks at 1338 and 1583 cm-1, which arose because of the D-band and G-band of assembled GO at the liquid-liquid interface of immiscible liquids, forming a hierarchical 3D arrangement after subsequent freezing and lyophilization. As depicted in Figure 4.11, the aerogel composed of GO (a) showcases ID/IG ratio of 0.928 that increased to 1.193 after thermal reduction at 800 °C under Ar for 1 h (b) because of the detachment of functional groups from the GO and remnant of structural defects on the surface of the GO. What is more, the non-reduced and reduced GO-Fe aerogels showed the same characteristics as neat GO. As evidenced in Figure 4.11 (c), the non-reduced GO-Fe aerogel demonstrated an ID/IG ratio of 0.838, which soared to 0.991 (d) upon thermal reduction, increasing the number of structural defects because of the thermal reduction at high temperatures. The lower ID/IG of non-reduced GO-Fe aerogel compared with non-reduced GO aerogel could be owing to the more dense composition of the GO-Fe aerogel's framework, leading to the formation of a well-packed 3D hierarchical arrangement of GO and magnetic GO. However, the GO-CNF aerogel showed different behavior than GO and GO-Fe aerogels. As depicted in Figure 4.11 (e), the non-reduced GO-CNF aerogel showed ID/IG of 0.931, which declined to 0.919 (f) upon carbonization of CNF and simultaneous thermal reduction of GO, leading to the formation of a 3D well-ordered framework with declined structural defects. This matter benefits applications requiring higher electron mobility and/or electrical conductivity, such as EMI shielding. 90 Figure 4.11. Micro-Raman spectroscopy results of (a) non-reduced GO aerogel, (b) reduced GO aerogel, (c) non-reduced GO-Fe aerogel, (d) reduced GO-Fe aerogel, (e) non-reduced GO-CNF aerogel, (f) reduced GO-CNF aerogel. The parallel beam X-ray diffraction technique based on a polycapillary collimating optic is employed to assess the composition and crystalline arrangement of formed hierarchical aerogel frameworks. This technique eliminates errors associated with the displacement of samples as well as instrumental errors that could lead to asymmetric peak broadening for samples with non-flat 91 and/or rough sources such as aerogels; hence, it provides the possibility for accurate and in-depth assessment of aerogel constructs and the hierarchical arrangements within them. Figure 4.12 demonstrates the X-ray diffractogram of developed aerogels consisting of GO, GO-Fe3O4, CNF, and a combination thereof. As depicted in Figure 4.12 (a), non-reduced GO aerogel showcases a sharp and well-defined peak at 2Ѳ of 10.7 with interlayer spacing (d-spacing) of 8.2 Å corresponding to the (001) crystalline plane of GO. This increase in the d-spacing compared with neat graphite with a d-spacing of 3.4 Å is due to the existence of oxygen-based functional groups on the GO that affected the distance between the GO layers 144. The second peak at 2Ѳ of 25.2 with a d-spacing of 3.5 Å is due to the stacking of GO sheets within the aerogel framework 145. Figure 4.12 (b) depicts the X-ray diffractogram of GO aerogel after thermal treatment at 800 °C for 1 h under Ar. As depicted, the reduced GO aerogel showed a well-defined peak at 2Ѳ of 25.9, corresponding to the d-spacing of 3.4 Å. The obtained d-spacing matches the interlayer spacing of graphite flakes, indicating the removal of oxygen-based functional groups, graphitization of the aerogel framework, formation of a well-oriented stacking arrangement among graphene sheets, and also restoration of a 𝜋-conjugated network within the graphene flakes assembled in a 3D hierarchical structure 144, 146. The other broad and weak peak positioned at 2Ѳ of 16.98 (d-spacing of 5.2 Å) shows the restacking of reduced graphene flakes and the existence of π- π stacking interactions in the cross-linked areas of the graphene flakes upon a decline in the hydrophilic functional groups (as also evidenced in FTIR spectrum) 144, 147. Figure 4.12 (c) illustrates the X-ray diffractogram of non-reduced GO-Fe aerogel. As depicted, this aerogel showcased two separate 2Ѳ peaks at 8.30 and 10.54, corresponding to the d-spacing of 92 10.64 and 8.38 Å. The first peak arises from the GO-Fe3O4 flakes, and the second peak is from the neat GO flakes. As evidenced in the X-ray diffractogram of neat GO-Fe3O4 flakes (see Chapter 3), immobilization of Fe3O4 on the GO flakes led to a decline in the interlayer spacing of the magnetic GO compared with GO. This matter clearly confirms the assembly of two different types of GO flakes within the aerogel framework. In addition, other appeared peaks in the XRD of GO-Fe aerogel at 2Ѳ of 30.23, 35.62, 43.20, 57.24, and 62.85 correspond to the (220), (311), (400), (511), and (400) crystalline planes of Fe3O4 nanoparticles showcasing the existence of magnetic nanoparticles in the aerogel framework 121. These outcomes clearly confirm the co-assembly of GO and GO-Fe3O4 in the GO-Fe aerogel’s hierarchical construct. The reduction of GO-Fe aerogel within the hydrothermal autoclave with hydrazine vapor at 100 °C changed the 2Ѳ peak of both GO and GO-Fe3O4 to 8.21 (d-spacing of 10.76 Å), showcasing the decline in the rate of oxygen-based functional groups which is in accord with obtained data from FTIR analysis (Figure 4.12 (d)). Other 2Ѳ peaks at 18.40, 30.16, 35.61, 43.21, 53.63, 57.22, 62.86, and 74.54 corresponding to the (111), (220), (311), (400), (422), (511), (400), and (422) crystalline planes of Fe3O4 nanoparticles. Moreover, Figure 4.12 (e) shows the XRD profile of non-reduced GO-CNF aerogel. This X-ray diffractogram showcases the main 2Ѳ peak of GO at 10.64 with an enlarged d-spacing of 8.31 Å compared with neat graphite (3.4 Å), indicating the existence of oxygen-based functional groups on assembled GO flakes within the aerogel framework. The broad and weak peak at 2Ѳ of 22.37 (d-spacing of 3.97 Å) corresponds to the (002) crystalline plane of native cellulose and is in accord with the card number JCPDS 03-0289. These outcomes clearly show the assembly of GO and CNF in the hierarchical 3D-arranged aerogel framework. However, the simultaneous thermal reduction of GO and carbonization of assembled CNF in the framework completely change the X-ray 93 diffractogram of reduced GO-CNF compared with the non-reduced one. As illustrated in Figure 4.12 (f), the thermally treated GO-CNF at 800 °C showed a broad peak at 2Ѳ of 25.74 with a d-spacing of 3.45 Å, near the d-spacing of graphite flakes. This outcome showcases the successful removal of the oxygen domains from graphene flakes and the formation of a 3D stacked arrangement between the graphene flakes and carbonized CNF. The obtained outcomes from the XRD analysis through the parallel beam technique showed the successful formation of hybrid aerogels with the desired compositions. Figure 4.12. X-ray diffractograms of (a) non-reduced GO aerogel, (b) reduced GO aerogel, (c) non-reduced GO-Fe aerogel, (d) reduced GO-Fe aerogel, (e) non-reduced GO-CNF aerogel, (f) reduced GO-CNF aerogel. 94 Tuning the composition of the liquid templates makes it possible to change the arrangement of the micro-scale pores within the filamentous aerogels after their lyophilization. Figure 4.13 (a) shows a schematic of the different constituents of the core-shell aerogel filaments. These filaments feature tunable internal micro-sale porosities within filamentous threads from (I) less densely packed hierarchical GO arrangement to (II) hybrid GO:GO-Fe3O4 or (III) GO:CNF frameworks with densified porosities. Figure 4.13 (b) shows the FESEM images of (I) the internal micro-scale porosities of GO and (II) the formation of a robust solid skin around the porous tubular framework of GO flakes. This interfacially driven robust skin comprised of NPSs is one of the main reasons for the mechanical integrity of the aerogels. The reduced GO aerogel had a high reversible compressibility, capable of reaching compressive strains of 90% and recovering its shape rapidly after force release (Figure 4.13 (c)). Such remarkable mechanical integrity arises from the robust skin around tubular filamentous constructs and the hierarchical GO framework within the core of filaments, enabling compression and shape recovery upon force release. This hierarchical framework results from basal connections of GO flakes, capable of withstanding high compressive strains 148. Indeed, common ultra-lightweight aerogels suffer from poor mechanical properties, and in most cases, they lose their shape if one touches them. However, the strategy described here generates handleable ultra-lightweight aerogel constructs realizing practical applications. As evidenced in the FESEM images (Figure 4.13 (b) (I-II)), lyophilization of the frozen filamentous liquid construct of GO, followed by thermal annealing, led to the formation of an aligned framework of internal micro-scale porosities. Upon incorporating GO-Fe3O4 nanomaterials into GO inks, a more densely packed micro-scale porous morphology is achieved (Figure 4.13 (d) I-II). Introducing naturally harnessed compounds such as CNF along with GO to the hierarchical construct and their simultaneous reduction/carbonization lead to the formation of 95 3D densely packed interconnected micro-scale porosity arrangements aligned in the direction of the filaments (Figure 4.13 (e) I-II). Compared with the previous practices in the field, the aerogels described here show one of the highest elastic resilience at a very low density of 3.12 mg cm-3 (Figure 4.13 (f) and Table 4.2), highlighting the remarkable potential of tunable aerogels in advanced applications due to the lightweight of the construct. The thickness of the interfacial solid skin as the main source of integrity and elastic resilience of the aerogels was examined by FESEM after lyophilization of the liquid templates (Figure 4.14). Three different GO aerogel samples (10 mg mL-1) were selected, and the thickness of the aerogel filaments’ skin was examined at 50 different spots. Image J software was used to extract the thickness distribution (Figure 4.15). As evidenced in Figure 4.13 (g) and Figures 4.14-4.15, average skin thicknesses of 189 ±29 nm, 182±23 nm, and 173±15 nm were found. The average skin thicknesses for the three aerogel samples were measured to be between 119-242 nm. The formation of NPSs at the interface creates a non-uniform skin around the liquid thread due to the random packing/stacking of NPSs, which is in agreement with previous studies 41. These densely packed NPSs assemblies could be governed by varying the pH of the medium (allow the protonation and deprotonation of functional groups), the concentration of ligands and NPs, the ionic strength of the aqueous phase, and the size of NPs 4. The controllable nature of the described process enables fine-tuning the aerogels’ micro-scale and macro-scale porosity levels by simply adjusting the processing conditions or manipulating the solid content in the inks. As evidenced in Figure 4.13 (h) and Figure 4.16, changing the concentration of GO from 1 mg mL-1 to 10 mg mL-1 led to a change in the average size of micro-scale porosities and their overall distribution range. As shown in Figure 4.17, the aerogels generated from 1, 3, 5, and 10 mg mL-1 aqueous GO suspension exhibited average micro-scale 96 porosity sizes of 105±32 µm, 88±24 µm, 83±19 µm, and 60±18 µm, respectively. Similarly, changing the gauge number of the injection needles from 27 (O.D. of 0.42 mm) to 15 (O.D. of 1.65 mm) considerably changed the macro-scale porosity level. As shown in Figure 4.18 (a), by changing the gauge number of the injection needle from 15 to 27, the volume of the aerogel increased by 32%, leading to a considerable macro-scale porosity enhancement. This is also accompanied by a variation of the aerogel filaments diameter, as reducing the needle size during the injection from gauge 15 to 27 could change the average diameter of filaments from 0.92±0.11 mm to 0.14±0.01 mm (Figure 4.13 (i) and Figure 4.18 (b-e)) after lyophilization. These results highlight the potential of the liquid templating approach in controlling the multi-level porosity of aerogels based on demand. 97 Figure 4.13. (a) Schematic illustration of the tunable internal micro-scale porosity of aerogel, including (I) GO aerogel, (II) GO-Fe aerogel, and (III) GO-CNF aerogel, via engineering the composition of manipulated NPs and subsequent treatment of the liquid template. FESEM images of tubular skin and internal micro-scale porosities of (b) (I-II) reduced GO aerogel and (c) the strain-stress curves of reduced GO aerogel at different compressive strains with six compression cycles at each respective strain rate; the inset shows the stress-strain curve of aerogels at 20% and 40% compressive strains. FESEM images of interfacially driven skin and micro-scale porosities of (d) (I-II) reduced GO-Fe aerogel and (e) (I-II) reduced GO-CNF aerogel. Scale bars are equal to (b) (I) 500 µm and (II) 200 µm, (d) (I) 200 µm and (II) 100 µm, and (e) (I-II) 50 µm. (f) Mechanical performance of the reduced GO aerogel compared with previous examples in the field. (g) The average thickness of aerogel skin in different samples. Tuning the (h) micro-scale pore size level of aerogels by changing the concentration of GO from 1 to 10 mg mL-1, and (i) manipulating the diameter of the filaments after lyophilization by changing the gauge number of the needle during ink injection or liquid templating. 98 Table 4.2. Mechanical performance of liquid templated aerogels compared with recent practices in the field by considering the density of aerogels. Aerogel Composition Processing Method Density (mg cm-3) Compression Strength (kPa) Compression Strain (%) Ref. Graphene aerogel FD 3-5 19 90 149 Carbon aerogels FD 22.4 0.8 50 150 NNC-CNT VD 10-54 497-651 70-90 151 Silsesquioxane aerogels VD 64-85 ~25-500 60 152 CNT aerogel VD 11.88 ~115 80 153 GNR aerogel VD 9.33 ~100 80 153 Graphene aerogel VD/AD 1-12 ~60 80 93 CNC aerogel FD 5.6 ~45 90 154 3D-printed graphene aerogel-PVA AD 6.5 ~55 10 155 Carbon aerogel FD 5.2 ~11 80 156 Graphene aerogel AD 2-10 ~9.5 50 157 Spherical graphene aerogel AD 5-7.8 45 95 158 Spherical rGO aerogel AD 5-7.8 140 95 158 Carbon aerogel SD 9.2 40 70 159 CNT-SiO2 nanofibrous aerogel FD 6.2 7 80 160 3D-printed Ti3C2Tx aerogel FD 9.73-15.69 1-4 50 161 Silica aerogel AD 64-98 ~240 55 162 Silica aerogel SD 53.5 35 90 163 Fibrous graphene aerogel FD 3.12 4.1 90 This Study Abbreviations: Freeze-drying (FD), native nanocellulose (NNC), carbon nanotube (CNT), vacuum-dried (VD), graphene nanoribbon (GNR), air-dried (AD), cellulose nanocrystal (CNC), polyvinyl alcohol (PVA), reduced graphene oxide (rGO), supercritical drying (SD), polymethylsilsesquioxane (PMSQ). 99 Figure 4.14. (a-c) FESEM images from the core and skin of 10 mg mL-1 GO aerogels at different magnifications (I-III). For an accurate assessment, three different samples were assessed, and the thickness of the skin was analyzed using Image J software over the whole skin profile. The scale bars are equal to (a) (I) 200 µm, (II) 50 µm, (III) 20 µm, (b) (I) 100 µm, (II) 20 µm, (III) 10 µm, (c) (I) 200 µm, (II) 50 µm, (III) 5 µm. 100 Figure 4.15. The thickness distribution range of GO aerogels’ skin generated via 10 mg mL-1 initial ink concentration related to (a) skin 1 (Figure 4.14 (a) III), (b) skin 2 (Figure 4.14 (b) III), and (c) skin 3 (Figure 4.14 (c) III) over the whole skin profile; the X-axis denotes the data point number with no specific order. As evidenced, the thickness of the skin is not uniform and varies within a specific range. 101 Figure 4.16. Change in the porosity level of GO aerogel upon changing the initial GO ink’s concentration. FESEM images showcase the porosity of aerogels formed with aqueous GO suspension with an initial concentration of (a) 1 mg mL-1, (b) 3 mg mL-1, (c) 5 m g mL-1, and (d) 10 mg mL-1 at different scale bars (I) 500 µm, (II) 200 µm, and (III) 200 µm. Figure 4.17. The pore size distribution and average pore size of GO aerogel generated via aqueous GO suspension with an initial concentration of (a) 1 mg mL-1, (b) 3 mg mL-1, (c) 5 m g mL-1, and (d) 10 mg mL-1; the X-axis denotes the data point number with no specific order. The corresponding images can be seen in Figure 4.16. 102 Figure 4.18. (a) Change in the volume of liquid templates and their corresponding macro-scale porosities upon changing the needle size from gauge 27 to gauge 15; the aerogels were prepared via injecting 2 mL of 10 mg mL -1 GO inks into the hexane domain containing 1 mg mL-1 POSS-NH2; the scale bar is equal to ~10.8 mm. FESEM images of aerogel filaments were generated via a needle with (b) gauge 27 and (c) gauge 15 with scale bars of (b) (I-III) 500 µm and (c) (I-III) 1 mm. Diameter distribution and average diameter of aerogel injected via a needle with gauges (d) 27 and (e) 15 into the POSS-NH2 domain; the X-axis denotes the data point number with no specific order. 103 4.7. Conclusions In summary, we developed a practical methodology for designing filamentous liquid templates with custom composition and arrangement for task-oriented aerogel production through freezing and lyophilization. The methodology enables the integration of NPs into structured liquids for the macro-scale manufacturing of filamentous aerogel constructs with controllable characteristics, porosity level (from micro- to macro-scale), 3D architectural design, morphology, responsiveness, and functionality. The ultra-lightweight aerogels, with densities ranging from 3.05 to 3.41 mg cm⁻3 in their reduced state, exhibited exceptional mechanical integrity, demonstrating 90% compressibility with rapid shape recovery. This effectively addresses a critical challenge in aerogel technology, i.e., brittleness and poor mechanical stability. The ability to engineer their design allows for precise customization of morphological features and overall properties, tailoring the aerogels to meet the demands of advanced applications. 104 Chapter 5: Functional Filamentous Aerogels The rapid pace of technological advancements has necessitated the development of a versatile material processing technique capable of tuning the final product's characteristics and features across multiple dimensions, from the nano- and micro-scale to the macro-scale. In Chapter 4, I presented a versatile aerogel manufacturing approach with the ability to engineer the composition, morphology, and features of the resulting filamentous aerogels on demand. Leveraging this advantage, I focused on developing advanced shielding systems with tunable shielding effectiveness and customizable EM wave attenuation mechanisms, whether absorptive or reflective, on demand. The controllable nature of the proposed methodology facilitated the achievement of tunable EMI shielding with exceptionally high specific shielding effectiveness, ranging from 31,739 to 39,893 dB cm2 g⁻1, depending on the aerogel composition. Notably, the ultra-lightweight nature of the aerogels, combined with their abundant porosity and hydrophobicity after reduction, enabled the realization of one of the highest oil absorption capacities ever reported, e.g., 487 times the initial weight of the aerogel for chloroform. Furthermore, their flexibility and electrical conductivity allowed for the development of sensitive piezoresistive sensors capable of monitoring human motion. Finally, the aerogels' potential for thermal insulation, infrared radiation blocking, and Joule heating was thoroughly explored. These remarkable properties stem from the engineerable nature of liquid templating, which pushes the boundaries of lightweight materials toward systematic functional design. 105 5.1. Experimental section 5.1.1. Materials The list of materials used for the synthesis of GO, mGO, and CNF, as well as aerogel manufacturing, was outlined in detail in Chapters 3 and 4. For the oil absorption section, chloroform, 1-butanol, and ethylene glycol were supplied by Sigma-Aldrich, silicone oil (PsF-5cst silicone oil fluids) was supplied by Clearco Products Co. Inc., diesel and gasoline were procured from local gas stations, and used or fresh car oil, as well as food oil and pump oil, was obtained from local stores. 5.1.2. Methods 5.1.2.1. Aerogel manufacturing The detailed aerogel manufacturing process is outlined in Chapter 4, where filamentous aerogels were meticulously engineered to meet the specific requirements of each application. This was achieved by leveraging the optimized conditions identified through the experimental analyses presented in the same chapter. 5.1.2.2. Electromagnetic interference shielding assessment Herein, the EMI shielding effectiveness of reduced/carbonized aerogels was examined within the X-band frequency range, i.e., 8.2-12.4 GHz, via a vector network analyzer (VNA) (Keysight model P9374A) equipped with a WR-90 rectangular waveguide. For this matter, the aerogel samples were attached to an offset and placed between the standard WR-90 waveguides connected to the VNA via microwave cables; a view of the VNA setup can be seen in Figure 5.1. 106 As illustrated in Figure 5.1, for each set of measurements, the VNA sends a signal from port one (S1) with a single defined frequency to the sandwiched sample; the receiver at the opposite side of the waveguide detects the reflected (S11) and transmitted (S21) EM waves, followed by measuring the phase data and magnitude of each received signal. Afterward, the same signal is sent to the sandwiched sample from port two (S2) with the same single frequency, followed by measuring the reflected (S22) and transmitted (S21) EM waves at the opposite side of the waveguide. Upon shift to the subsequent frequency, the measurements are made similarly. At the end of assessment cycles, the measured reflection and transmission values are presented as complex S-parameters 64. The collected S-parameters are thence employed to measure the EMI shielding coefficients, including reflectance (R), absorbance (A), and transmittance (T). The reflectance, which defines by R, is the power of the reflected wave over the incident wave (PR/PI). This coefficient can be measured based on the complex S11 parameter using the following equation: R =PRPI= |𝑆112| = |𝑆222| (5.1) In which the S11 is the complex scattering parameter measured according to the magnitude of the reflected voltage over the incident voltage at port one. The transmittance or T coefficient is the power of the transmitted wave over the incident wave (PT/PI) and can be calculated through the S21 parameter as follows: T =PTPI= |𝑆212| = |𝑆122| (5.2) Where the S21 defines as the magnitude of the transmitted voltage from port one to two divided by the magnitude of the incident voltage at port one. The absorbance or A coefficient can be measured via the following relation: A = 1 − R − T (5.3) 107 The main EMI shielding mechanism of EM shields can be accurately defined in terms of EMI shielding coefficients. In this regard, if the absorbance (A) becomes higher than reflectance (R), the dominant shielding mechanism is based on absorption, whereas a higher R than A means the dominant reflection mechanism, i.e., R˃0.5 or A˂0.5 is reflection-dominant, and R˂0.5 or A˃0.5 is absorption-dominant shielding mechanism 64. Figure 5.1. A view of the VNA setup and its crucial parameters, adapted with permission from ref. 110. Along with the shielding coefficients, the shielding effectiveness, which is known as the total EMI shielding effectiveness (SET), is also a crucial and widely used parameter to assess the shielding performance of EMI shielding materials or structures. The SET represents the effective safeguarding role of a shield against incident EM waves. The SET was measured by the sum of the reflection loss (SER) and absorption loss (SEA) 66-69: SET = SER + SEA (5.4) For measuring the SER from both the front and back interfaces of a shield, the simplified version of Fresnel’s equation for an electrically conductive shield can be used, which can be described as following 60: 108 SER(dB) = 10 log ( 11 − R ) (5.5) The absorption loss parameter (SEA) can be measured by the following formula: SEA(dB) = 10 log ( 1 ― R T ) (5.6) For porous and lightweight shielding systems such as aerogels, it is essential to measure the specific shielding effectiveness (SSE) over thickness (SSE/t) that relates both the density and thickness of the shield to SET. The SSE/t can be measured via the following formula 65: 𝑆𝑆𝐸/𝑡 =𝑆𝐸𝑇ρ ∗ t (5.7) In which t and ρ are correspond to the thickness (cm) and density (g cm-3), respectively. 5.1.2.3. Oil absorption The oil or solvent absorption capacity of double-step reduced GO aerogels was assessed against different oils/solvents, including chloroform, silicone oil, ethylene glycol, vacuum pump oil, diesel oil, gasoline, 1-butanol, food oil (canola oil), and motor oil (fresh and used). For this matter, the initial weight of the aerogels (W0) was measured to four decimals using an analytical grade balance and thence, the aerogels were immersed into the target oil/solvent for 3 min. The swollen aerogels were then taken out of the liquid and weighted (Wa) after the sample surface was wiped with a filter paper to remove excess solvent/oil; three samples were used for each respective assessment. The absorption capacity of the aerogels was measured via the following formula: Absorption capacity (%)= (Wa-W0)/W0 × 100% (5.8) The reusability of aerogels for absorption/desorption of diesel as a representative of assessed oils/solvents was performed by squeezing the aerogel to remove the absorbed liquid. The aerogel weight prior to the absorption of the liquid, after absorption, and after desorption by squeezing to 109 remove the liquid was measured during each cycle. Because of the fast oil absorption kinetic of the aerogels owing to their multi-scale porosities, aerogels were squeezed on an absorptive pad to remove the captured oils and perform the reusability test. Of note, for oil absorption tests, GO aerogels were initially placed within a 3 MPa autoclave containing 10 mL 50-60% hydrazine hydrate, followed by treatment at 100 °C for 24 h. The initially reduced aerogels were then treated at 800 °C for 1 h under an Ar atmosphere. 5.1.3. Characterization The nanomaterials and aerogels characterization were performed according to the protocols outlined in Chapters 3 and 4. The piezoresistive sensing capability of the aerogels and the associated signals were acquired using a multi-channel Autolab model M204. The thermal insulation, infrared radiation blocking, and Joule heating capability of the filamentous aerogels were examined using the FLIR E8 infrared camera. 5.2. Design and manufacturing of functional aerogels 5.2.1. Engineerable electromagnetic shielding systems The interfacially driven morphologies lock in the characteristics of engineered NPs into the final liquid construct, resulting in a liquid template for developing engineerable/reconfigurable ultra-lightweight aerogels with well-defined nano-, micro-, and macro-scale characteristics. Such a function-led design control over structure and composition offers many advantages for engineering desired functionalities within the aerogel framework for electromagnetic protection and environment-related applications. As a proof of concept, 3D fibrous electromagnetic interference (EMI) shields with tunable shielding characteristics were fabricated. These shields can mitigate the adverse effects of EM 110 waves on the health of living creatures and safeguard the proper performance of electronic equipment 110. As an essential requirement for EMI shielding, the electrical conductivity of GO, GO-Fe, and GO-CNF aerogels was enhanced by thermal annealing, reaching a conductivity of 0.117, 0.110, and 0.356 S/cm (Figure 5.2 (a)), respectively, at a thickness of 4 mm for the developed frameworks. Notably, the aerogel frameworks were ultra-lightweight with densities between 3.05-3.41 mg cm-3 after the reduction process (Figure 5.2 (b)), rendering them practical for applications where weight is a major concern, such as aerospace. Of note, the density of aerogels was measured by calculating the volume and weight of five different aerogel samples and considering the average value. The unique multi-scale porosity, high electrical conductivity, and the customizability of nano-scale building blocks render these aerogels an engineerable 3D filamentous framework for generating EMI shielding with an on demand dominant shielding mechanism. An overview of the shielding characteristics of these aerogels is given in Figures 5.2 (c) & (d) and Figure 5.3. The thermally reduced GO aerogel had a reflection-dominant (R: 0.54 and SER: 3.41 dB) shielding characteristic with excellent absorption loss (SEA) of 36.23 dB, total shielding effectiveness (SET) of 39.64 dB, and specific shielding effectiveness (SEE/t) of 31,739 dB cm2 g-1. These shielding characteristics arise from different phenomena. A portion of the EM wave incident on the surface of a conductive shield is reflected, owing to the impedance mismatch between free space (377 Ω) and the shield's surface 110. Reflection is the dominant shielding mechanism for highly conductive EM shields such as metals because of the enforced oscillation of free-charge carriers in response to incident EM waves, generating a scattered field as reflection. The portion of the EM waves that penetrates the aerogels faces numerous interfaces with impedance mismatches due to the multi-scale (from micro-scale (in the core of filaments) to 111 macro-scale (between filaments)) porosities. These porosities contribute to the multiple internal reflections of the EM waves within the aerogel framework, prolonging their propagation pathway prior to transmission and thus dissipating EM waves in the form of heat. This leads to absorption because of the interaction of EM waves with electrically conductive components and/or electrical/magnetic dipoles 110. Considering the governing factors in EMI shielding, it is possible to further enhance the shielding performance of the aerogels by tuning their nano-scale composition and micro-/macro-scale porosity by engineering the templated liquids. Here, the introduction of GO-Fe3O4 to the aerogel framework boosted the SEA and SET to 45.72 dB and 48.49 dB, respectively, with a dominant absorption mechanism (R: 0.46 and SER: 2.76 dB) and remarkable SEE/t of 39,692 dB cm2 g-1. This considerable increase in the shielding and change in the nature of the shield from a reflector to an absorber at the same ink concentration (1 wt%) arises from an increase in the internal micro-scale and macro-scale porosities, as evidenced by the FESEM images (see Chapter 4). This increase in the porosity level enhances internal scattering between alternating magnetic/conductive domains, contributing to the dissipation rate of EM waves. More importantly, the introduction of nano-scale magnetic components enhances frequency-dependent magnetic losses. Thus, within the X-band frequency range (8.2-12.4 GHz), EM wave dissipative factors such as eddy current loss and natural resonances are activated, further improving EM shielding performance 164. The carbonization of natural compounds, like CNF, within the aerogel framework, along with the GO reduction, leads to a further increase in the level of micro-scale porosity and electrical conductivity (Figure 5.2 (a), FESEM images were illustrated in Chapter 4). For example, the carbonized/reduced GO-CNF aerogel showed a remarkable SEA of 50.01 dB, SET of 54.47 dB, 112 and SEE/t of 39,893 dB cm2 g-1 with a reflection-dominant characteristic (R: 0.63 and SER: 4.45 dB) because of the enhanced electrical conductivity, increasing the impedance mismatching. These results dramatically show that the controllable shielding behavior of the aerogels is due to the multi-scale tunability of the templated liquid, i.e., tunable nano-scale building blocks and micro-/macro-scale porosities. Figure 5.2 (e) shows a schematic of the shielding mechanism of the aerogels by engineering their structure via macro-scale manufacturing, micro-scale assembly, and nano-scale chemistry. The EM characteristic of the aerogels developed here is compared with other aerogels reported previously in terms of their specific shielding effectiveness (Figure 5.2 (f) and Table 5.1) and absorbance (Figure 5.2 (g) and Table 5. 2) at a low ink concentration (1 wt%). Figure 5.2. (a) Electrical conductivity of the aerogels after thermal annealing at 800 °C for 1 h under Ar, (b) the density of aerogels before and after thermal reduction. (c) Shielding coefficient, and (d) EMI shielding performance of the reduced aerogels within the X-band frequency range (8.2-12.4 GHz). (e) Schematic illustration of shielding behavior of multi-scale aerogel shields made of (I) reduced GO aerogel, (II) reduced GO-Fe aerogel, and (III) reduced GO-CNF 113 aerogel. (f) The density-dependant shielding effectiveness of thermally annealed (800°C for 1 h under Ar) engineerable aerogels compared with recent practices in the field, and (g) comparing the total shielding and absorbance of the thermally reduced engineerable aerogels compared with recently developed shields; the reported values showcase the controllable shielding characteristics of the generated aerogels. Figure 5.3. EMI shielding performance of (a-b) reduced GO aerogel, (c-d) reduced GO-Fe aerogel, and (e-f) reduced GO-CNF aerogel at port one and port two within the X-band frequency range (8.2-12.4 GHz); the uniform and nearly equal data from both ports show the reliability of the test and similar morphology of the aerogel at both sides. 114 Table 5.1. A view of specific shielding effectiveness of developed engineerable aerogels compared with previous studies. Material Thickness (mm) Electrical Conductivity (S/m) EMI SE (dB) Density (mg/cm3) SSE/t (dB cm2/g) Ref. rGO 2.5 4.85 40.2 4.5 35730 165 rGO-PDMS ~1.5 - 53 122 2890 166 rGO aerogel 0.12 2.5×105 ~70 410 25600 167 rGO-epoxy 4 95 35 4 21800 168 rGO aerogel 2.5 179 27.6 5.5 20070 169 rGO-melamine 40 0.026 37.2 11 850 170 rGO-PDMS 5 0.5 65 4.2 29500 171 rGO-Ti3C2Tx 3 1,000 50.7 46 36737 172 rGO-Ti3C2Tx 2 1,085 52.7 440 5288 173 Ti3C2Tx 2 2,200 ~62 6.3 49500 174 Ti3C2Tx 1 - 70.6 11 64182 62 Ti3C2Tx 1 - 44.8 6 81455 62 Ti2CTx 1 - 69.2 11 62909 62 Ti3CNTx 1 - 54.1 11 49182 62 Ti3C2Tx foam 0.006 5.8×105 32 390 136752 175 Ti3C2Tx-CA 0.026 1.3 54.3 1190 17500 176 Ti3C2Tx-carbonized wood 3 3520 71.3 197 1200 177 Ti3C2Tx-AgNWs 2 2,450 52.6 490 5313 178 Ti3C2Tx-CNTs 3 9,430 104 420 8253 179 Ti3C2Tx-SA-PDMS 2 2,211 72 20 18000 180 CNTs-cellulose 2.5 1.8 20.8 95 875 181 CNTs-carbonized cellulose 2 263.4 96.4 30.5 15800 182 CNTs-ANFs 0.168 230 22.7 43 33528 183 C-cenosphere 10 940 ~47 32 142 184 C-SiC nanowires 4 223 ~47 590 198.8 185 Stainless-steel fiber-PP 3.1 ~0.5 48 640 242 186 Phthalonitrile-based carbon foam 2.4 240 51.2 154 1705 187 Reduced GO aerogel 4 117.62 39.64 3.12 31739 This Study Reduced GO-Fe aerogel 4 110.73 48.49 3.05 39692 Reduced GO-CNF aerogel 4 356.80 54.47 3.41 39893 Abbreviations: Polydimethylsiloxane (PDMS), aramid nanofiber (ANF), calcium alginate (CA), silver nanowires (AgNWs), sodium alginate (SA), polypropylene (PP). Table 5.2. Electromagnetic shielding performance of reduced engineerable aerogels compared with the recent practices in the literature. Sample Thickness (mm) EMI SE (dB) SER (dB) R A Ref. Ti3C2Tx 0.001 46.1 13.5 ~0.96 ~0.04 188 3D graphene fibers 0.0263 56 ~9 ~0.89 0.11 189 rGO film 0.0084 20 ~8 ~0.84 ~0.16 190 Ti3C2Tx-PS 2 61.2 6.5 ~0.78 ~0.22 191 SWCNTs-Ti3C2Tx-latex 1.1 52 ~19 ~0.98 ~0.02 192 CNT-graphene core-shell hybrid foam 1.6 38.4 3.9 0.59 0.41 193 MWCNTs-WPU foam 2.3 50.5 ~9 ~0.89 ~0.11 194 Glucose-derived carbon films 0.00048 21.72 7.96 0.84 0.16 195 CNTs sponge-epoxy 2 44 5 ~0.68 ~0.32 196 115 Sample Thickness (mm) EMI SE (dB) SER (dB) R A Ref. Coupled ANF-PVA hydrogel with AgNWs-PVA ~0.3 52 16 ~0.97 ~0.03 197 PCC-MXene-PVA composite 0.048 43.1 13.17 ~0.96 ~0.04 198 AgNWs decorated leather 0.5 55 ~8 ~0.84 ~0.16 199 Wrinkled Ti3C2Tx 0.02 68 27 0.99> <0.01 200 MWCNTs-Fe3O4@Ag-epoxy 2 35 4.5 0.65 0.35 201 Neat Ti3C2Tx 0.014 82 ~20 ~0.99 ~0.01 202 AgNWs-carbon hybrid sponge 3 70.1 ~11 ~0.91 ~0.09 203 Electrospun PVA-Fe3O4/PVA-Ti3C2Tx/ PVA-Fe3O4 nanofiber shield 0.075 40 ~13 ~0.96 0.04 80 MWCNTs-PLLA 1.5 30 4 0.6 0.4 204 MWCNTs-PVDF 1 22.5 6.3 0.77 0.23 205 CNTs-rGO foam 2 31.2 5.9 0.74 0.26 206 rGO-PDMS 5 26 2.99 0.49 0.51 7 rGO foam 0.9 42.3 10 0.9 0.1 207 CNTs-GTR 1 30 6 0.75 0.25 208 Graphene-Fe3O4 papers 0.25 24 8 0.84 0.16 209 Ti2CTx-PVA 0.3 21 11 0.91 0.09 210 Ti2CTx-PVA foam 5 28 2 0.37 0.63 210 Multilayer Ti3C2Tx-CNF 0.035 39.6 17.7 0.98 0.02 211 Graphene/MWCNTs/PMMA 2 36 6.67 0.78 0.22 212 Multilayer Fe3O4@rGO-MWCNTs-WPU 0.8 36 1.46 0.27 0.73 213 Ti3C2Tx-PEDOT:PSS aerogels 5 28 3 0.5 0.5 214 Multilayer PVA-Ti3C2Tx 0.027 44.4 8.3 0.85 0.15 215 PMMA-Fe3O4@rGO 2.9 29.3 4 0.6 0.4 216 Ti3C2Tx-ANF 0.018 55.9 10.3 0.9 0.1 217 FGQF 1.12 106 ~10 ~0.9 ~0.1 218 FGQF 0.2 ~48 ~9.6 ~0.89 ~0.11 218 Ti3C2Tx-polyaniline-carbon fiber 0.55 26.5 5.7 0.74 0.26 219 Nacre-shaped graphene-PI 0.01 43.8 ~13.3 ~0.95 ~0.05 220 Polyaniline-grafted Ti3C2Tx-PVDF 1.7 33.3 5.2 0.7 0.3 221 MXene-functionalized PEDOT:PSS hydrogel 0.295 51.7 3.7 0.58 0.42 222 Silver-electrospun nylon nanofiber 0.005 77.6 13 ~0.95 ~0.5 223 Ionic liquid doped PEDOT:PSS hydrogel 0.046 54 ~18.4 ~0.98 <0.02 224 Ti3C2Tx-gelation 0.004 53.6 ~19.2 ~0.98 <0.02 225 Honeycomb porous graphene-AgNWs 0.0483 61.8 ~14.5 ~0.96 ~0.04 226 Ti3C2Tx-MWCNTs-SrFe12O19 0.04 62.9 ~12 ~0.94 ~0.06 227 Screen-printed Ti3C2Tx-Xanthan Gum 0.012 40.1 ~15 ~0.97 ~0.03 228 Ti3C2Tx 0.005 57.4 17.5 ~0.98 ~0.02 229 AgNWs-nanocellulose aerogels 2 70.5 ~17 ~0.98 ~0.02 78 Ti3CNTx 0.005 49.7 17 ~0.98 ~0.02 229 MWCNTs-WPU 2.3 46.7 ~7.2 ~0.8 ~0.2 230 2D Cu nanosheets 0.063 105 ~14 ~0.96 ~0.04 231 CNTs-ANFs hybrid aerogel 0.568 54.4 ~8 ~0.84 ~0.16 183 Polyolefin-Ti3C2Tx-graphene 1.85 61 7.7 0.83 0.17 232 Cu NWs-graphene core-shell aerogel 5 43.7 2.86 ~0.48 ~0.52 233 Compressed Cu NWs-graphene core-shell aerogel 5 31.28 4.11 ~0.61 ~0.39 233 Ti3C2Tx-polydopamine hybrids 0.007 58.4 ~16 ~0.97 ~0.03 234 Graphite film ~0.0004 27.8 ~5 ~0.69 ~0.31 235 Laminated ANF-CNTs 0.024 36 ~14 ~0.96 ~0.04 236 Ti3C2Tx-CNF 0.074 25.8 5.3 ~0.71 ~0.29 237 CF 0.032 45 ~16 0.97 0.03 238 116 Sample Thickness (mm) EMI SE (dB) SER (dB) R A Ref. Densified CNT film ~0.015 101 ~20 ~0.99 ~0.01 239 Ti3C2Tx-rGO aerogel 2 56.4 5.7 0.73 0.27 173 CF-NiCo2O4–4F 0.034 53 ~8.2 0.85 0.15 238 rGO wrapped AgNWs networks ~0.0001 35 8.1 ~0.84 ~0.16 240 Polydopamine-modified expanded graphite-PI 0.5 101 ~19 ~0.98 ~0.02 241 Carbonized wood-Ni-CNTs - 48.2 2.8 ~0.47 ~0.53 242 Ti3C2Tx-ANF 0.037 48 ~18 ~0.98 ~0.02 243 SrGO-(C-SiC)12 4 70.2 ~12 ~0.94 ~0.06 244 CF-NiCo 0.034 45 ~10 0.90 0.1 238 Recycled carbon fibers-Ti3C2Tx 0.343 45.7 ~15 ~0.97 ~0.03 245 Reduced GO aerogel 4 39.64 3.41 0.54 0.45 This Study Reduced GO-Fe aerogel 4 48.49 2.76 0.46 0.53 Reduced GO-CNF aerogel 4 54.47 4.45 0.63 0.36 Abbreviations: Polystyrene (PS), water‐borne polyurethane (WPU), aramid nanofibers (ANF), silver nanowires (AgNWs), phase change capsules (PCC), polyvinyl alcohol (PVA), poly(L-lactide) (PLLA), ground tire rubber (GTR), cellulose nanofiber (CNF), poly (methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), ferromagnetic graphene quartz fiber (FGQF), polyimide (PI), carbon fabric (CF). 5.2.2. Oil absorption capacity of filamentous aerogels One of the most formidable global threats stems from the leakage of crude or heavy oil, as well as highly toxic organic solvents, into the environment. These leaks endanger marine life, contaminate seafood, pollute freshwater sources, and introduce a considerable volume of toxic compounds into the ecosystem. This issue gives rise to substantial ecological, economic, and health concerns in affected areas. As such, it necessitates the development of effective solutions capable of overcoming the common drawbacks of conventional methods. These disadvantages include the release of toxic dioxins due to oil combustion, subpar solvent or oil adsorption efficiency, prohibitive production costs, inadequate recyclability, and compromised structural integrity. 246, 247. We addressed this global challenge using mechanically robust, multi-scale porous hierarchical aerogel constructs capable of effectively recovering a large amount of toxic oils or solvents without causing secondary pollution. To demonstrate the practicality of the aerogel constructs for global oil/solvent contamination, a wide range of highly contaminating and widely used solvents/oils were selected, from low-density 117 and highly volatile ones to heavier oils/solvents. For this purpose, the tubular solid-like layer around the filamentous threads generated from the NPS derivatives, i.e., siloxane groups of POSS-NH2 and reduced GO flakes, makes the aerogel construct hydrophobic (contact angle of 120.5°) with a remarkable superoleophilicity (Figure 5.4 (a) (I-III)). Due to the abundant micro-scale porosities within the filamentous aerogels and the macro-scale porosities between the filaments, the aerogels offered an exceptional oil absorption rate and capacity (Figure 5.4 (b)). The double-reduced GO aerogel had one of the highest oil absorption capacities ever achieved by absorbing chloroform, diesel oil, motor oil, and pump oil more than 466±21, 345±22, 204±6, and 266±35 times of its original weight, respectively, which was found to be nearly density-dependent (Figure 5.4 (c)). Notably, the double-reduced GO aerogels were generated upon an initial reduction via hydrazine vapour at 100 °C followed by thermal annealing at 800 °C for 1 h under Ar. Outstanding properties of these aerogels, including mechanical robustness and an extremely flexible structure, enable repeated absorption-desorption cycles without considerable changes in their absorption capacity (Figure 5.4 (d)). We note that the ease of processing and scalability of the process render it a versatile approach to meeting industrial demands at large scales. The aerogel, saturated with the oils, maintained its mechanical integrity and flexibility, and released the absorbed oil simply by squeezing (Figure 5.4 (e)); as demonstrated, upon oil desorption by compression, the aerogel promptly recovers its initial shape without any visible plastic deformation, attesting to its elastic resilience and superior compressive resistance (Figure 5.4 (e)). The aerogel could also simply float on the surface of the water, rapidly separating the oil from the water in less than 5 s (Figure 5.4 (f)), rendering these aerogels appealing for oil spill remediation. The fact that these novel porous ultra-lightweight solids feature exceptional oil absorbance properties (Figure 5.4 (g) and Table 5.3) coupled with straightforward processability will empower 118 them to challenge current market solutions. Besides, such recoverability, fast absorption kinetics, prevention of secondary pollution, and controllable structural features make these aerogels a versatile framework for the effective cleanup of nature from hazardous oil/solvent pollution. Figure 5.4. (a) Digital image of (I) hydrophobic double-reduced GO aerogel and (II-III) its hydrophobicity assessment via sessile drop technique, (b) oil absorption performance of the double-reduced GO aerogels, (c) oil absorption rate over the density of absorbed oils, (d) oil absorption-desorption stability of the double-reduced GO aerogel, (e) prompt oil absorption-desorption cycle of double-reduced GO aerogel upon squeezing, (f) rapid absorption and separation of the used motor oil from the aqueous system via the double-reduced GO aerogel, and (g) oil absorption record of the as-developed aerogels compared with existing records; in the image, the overall amount of weight gain after oil absorption compared with the initial weight of the aerogel and the oil absorption enhancement is compared with the best practices in the field; the X-axis denotes the data point number with no specific order. Scale bars are equal to (a) (I) ~10.7 mm, (e) (I) ~9.4 mm, (II) ~9.8 mm, (III) ~10.1 mm, and (f) (I) ~9.2 mm, (II) ~9.1 mm, (III) ~9.1 mm. The reported scale bars in parts (a), (e), and (f) are approximate. 119 Table 5.3. Oil/organic solvent absorption of the double reduced GO aerogel compared with previous practices in the literature. Sorbent Flexibility Sorbent Density (mg cm-3) Type of Oil/Solvent Sorbent Capacity (%) Ref. Fluorinated GO-agarose-organosilane aerogel Compressible, 50% 2373.04 Diesel Chloroform Motor Oil Mineral Oil 13000 18500 13500 14000 248 PVA-GO aerogel Compressible, 50% 1740.04 Diesel Chloroform Motor Oil Mineral Oil 11500 16000 12500 13000 248 Gelatine-GO aerogel Compressible, 50% - Diesel Chloroform Motor Oil Mineral Oil 10400 15400 12000 12500 248 Silylated chitosan aerogel Compressible, 60% 14.3-35.6 Chloroform Pump Oil 6200 4400 249 KF-SA aerogel Compressible, 60% 38 Diesel Pump Oil 3700 4400 250 Stereocomplexed PLA-based aerogel - - Pump Oil 2300 251 Self-assembled graphene aerogels - - Diesel Chloroform Motor Oil Pump Oil Machine Oil 6000 8000 3200 5800 4400 252 Peanut hull-graphene aerogel - - Diesel Chloroform Motor Oil Pump Oil Machine Oil 3600 5800 1000 3700 2000 252 Chitosan aerogel - - Diesel 3000 253 Magenetic chitosan aerogel - - Diesel 2800 253 Hydrophobic chitosan aerogel - - Diesel 2400 253 PVA-CNF aerogel - 4.66-16.54 Chloroform 14000 254 Chitosan-cellulose aerogel - 55 Diesel Gasoline Pump Oil Silicone Oil 1500 1490 1650 1900 255 NFC-SAC aerogel Compressible, 85% 7-20 Pump Oil Chloroform 6200 9500 256 NFC-PVA-SAC aerogel Compressible, 85% 7-20 Pump Oil Chloroform 5000 8300 256 CNF-chitosan aerogel Compressible, 60% 8.4 Gasoline Motor Oil Pump Oil 14500 16000 16500 257 CN-GO aerogels Compressible, 80% 2-3 Gasoline Pump Oil 19500 19000 258 Amphipathic graphene aerogel Compressible, 50% 4.9-10 Chloroform 25000 259 Dopamine-functionalized CNT-polyimide aerogel Compressible, 40% ~195-220 Silicone Oil 450 260 120 Sorbent Flexibility Sorbent Density (mg cm-3) Type of Oil/Solvent Sorbent Capacity (%) Ref. Carbon aerogel Compressible, 70% 25.5 Gasoline Diesel Chloroform 1390 1280 1685 261 Methyltrimethoxysilane-coated recycled PET aerogel - 7-18 Motor Oil 5800 262 Perfluorooctyltrimethoxysilane modified biomass carbonaceous aerogel - - Chloroform 1500 263 Cotton-cellulose aerogels - - Motor Oil 6000 264 PET aerogel - 31.1 Chloroform Pump Oil 3800 2800 265 Bacterial cellulose-silica aerogels Compressible, 80% 63 Gasoline Pump Oil Motor Oil 1100 900 750 266 Graphene-PVA-CNF aerogel Compressible, 50% 6.17 Used Pump Oil Pump Oil 9000 11000 267 Anisotropic graphene-PVA-CNF aerogel Compressible, 50% 6.17 Used Pump Oil Pump Oil 16000 17500 267 Kapok-microfibrillated cellulose aerogels - 5.1 Gasoline Pump Oil Motor Oil 10700 12300 12200 268 Micro-cellular polymer foam - - Engine Oil Diesel 3200 2200 269 Biomass carbon fiber aerogel - 28.92 Diesel Pump Oil 3300 4300 270 BPWP hybrid aerogel - 15 Pump Oil Chloroform 11600 9200 271 Ordered hollow nanofiber aerogel Compressible, 60% 12.16 Diesel Pump Oil 7200 6200 272 Sisal-reinforced biomass carbon aerogel - - Diesel Pump Oil 9500 12000 273 Biomass carbon aerogels - - Engine Oil Diesel 12000 9000 274 Macroporous cellulose aerogel Flexible 41 Diesel Gasoline Chloroform 2500 2300 4200 275 biomass carbon aerogel - 112 Diesel Gasoline Chloroform Pump Oil 8800 8500 8300 9200 276 Functionalized graphene aerogel Compressible, 30% 14.4 Chloroform Pump Oil 8000 4000 277 Graphene aerogel Compressible, 30% 14.4 Chloroform Pump Oil 11000 5800 277 Biomass carbon-SiO2-MnO2 aerogel - - Diesel Pump Oil 7800 10500 278 Wood aerogel-PDMS Compressible, 80% 74.8 Pump Oil 1200 279 Reduced PI-GO aerogel - 90.5 Silicone Oil Pump Oil 16000 14000 280 Carbon aerogels Compressible, 80% 8.3 Chloroform 6500 281 121 Sorbent Flexibility Sorbent Density (mg cm-3) Type of Oil/Solvent Sorbent Capacity (%) Ref. Nanocellulose-graphene aerogel Compressible, 90% 16 Chloroform Silicone Oil 5700 3600 282 Calcination MF-graphene aerogel - 5 Diesel 24000 283 Calcination graphene aerogel - - Diesel 16000 283 MF-graphene aerogel - - Diesel 11000 283 Graphene aerogel - - Diesel 7000 283 Paper waste aerogel - 11.4 Chloroform Pump Oil 11000 5800 284 PS-Fe3O4-graphene aerogel Compressible, 80% 5 Diesel 3000 285 Graphene-cellulose-silica aerogel - - Gasoline Chloroform 42 68 286 Biomass carbon aerogel-TiO2 nanorods - - Diesel Pump Oil 8200 10500 287 Cellulose-epoxidized soybean oil aerogels - 26.7-72.8 Silicone Oil Pump Oil 3400 2800 288 Graphene aerogel Compressible, 60% 4.2 Diesel Gasoline Chloroform 25000 15000 32000 289 SA aerogel - - Diesel 23000 290 Waste cardboard aerogels - 38-48 Diesel Chloroform 4200 4500 291 Bioinspired aerogels Compressible, 40% 54 Diesel Pump Oil 5400 5600 292 Bacterial cellulose aerogels - 6.77 Diesel Gasoline Chloroform 11000 9200 18000 293 Cellulose nanofibril aerogels Compressible, 80% 23.2 Chloroform 4500 294 Carbon aerogels Compressible, 80% 4.3 Chloroform Pump Oil 16000 10000 295 CNF aerogel-core shell magnetic NPs composite Compressible, 90% 7 Diesel Gasoline 6800 5900 296 MFC aerogel Compressible, 70% 5.08 Gasoline Chloroform Motor Oil Pump Oil Mineral Oil Silicone Oil 12500 26000 15400 15500 14800 15500 297 Cellulose-based aerogel Compressible, 80% 10.2 Diesel Chloroform Mineral Oil Corn Oil Gasoline Pump Oil Motor Oil 7200 9900 8300 6300 5500 6300 7600 298 Functionalized cellulose aerogel - 4.56-11.23 Gasoline Pump Oil 8000 9000 299 Wood-based superhydrophobic aerogel Compressible, 40% - Diesel Motor Oil Pump Oil 2000 2200 2250 300 Graphene foam - - Diesel 6000 301 122 Sorbent Flexibility Sorbent Density (mg cm-3) Type of Oil/Solvent Sorbent Capacity (%) Ref. Gasoline Chloroform Pump Oil 3700 19000 7000 CF aerogel - 12 Chloroform Pump Oil 11200 19000 302 Hydrophobic nanocellulose aerogels - 20-30 Chloroform Mineral Oil 4000 3000 303 Carbon aerogel Compressible, 50% 24-95 Chloroform Gasoline Pump Oil 1260 700 760 304 Superhydrophobic silica aerogel - 80 Gasoline 880 305 Graphene-PVDF aerogel Compressible, 80% - Chloroform Pump Oil 4900 2500 306 Graphene-PVDF aerogel with changed content Compressible, 80% - Chloroform Pump Oil 6500 4600 306 CNF aerogel Compressible, 60% 1.7-8.1 Chloroform Pump Oil 33000 23000 307 Cellulose-based aerogel - 34 Diesel Chloroform Pump Oil Motor Oil 2200 4150 2300 2000 308 Superhydrophobic silica aerogels reinforced with polyacrylonitrile fibers Compressible, 80% 1.67 Diesel Chloroform 1070 1400 309 Gelatin aerogels Compressible, 70% 5-8 Chloroform Gasoline Waste Pump Oil Pump Oil Silicone Oil 12000 8000 10400 11900 11800 310 CNF aerogel - - Pump Oil 1400 311 rGO-CNF aerogel - - Pump Oil 2800 311 rGO-trimethyl chlorosilane-coated CNF aerogel - 6.78 Pump Oil 3400 311 CNF-MWCNT carbon aerogel Compressible, 70% 56 Chloroform Gasoline Pump Oil Motor Oil 8500 5100 11500 7200 312 Bacterial cellulose aerogel - 3.9-10.8 Pump Oil 9000 313 PDMS-decorated Magnetic chitosan-based aerogel - 65.5 Diesel 1200 314 Graphene-CNT aerogel - - Diesel Gasoline Pump Oil 16000 14500 18000 315 WBF-based Silane cellulose aerogel Compressible, 80% 85-144 Diesel Gasoline Waste Pump Oil Pump Oil 700 900 900 830 316 Magnetic carbon fiber aerogel - - Chloroform Pump Oil 6800 6300 317 Ultralight carbon aerogel - 10 Diesel 7200 318 123 Sorbent Flexibility Sorbent Density (mg cm-3) Type of Oil/Solvent Sorbent Capacity (%) Ref. Pump Oil 5500 CNF-silica fiber-Fe3O4 aerogel Compressible, 50% 22.3 Chloroform Gasoline 10500 5200 319 Sponge-reinforced silica aerogel Compressible, 80% 114-585 Motor Oil 3700 320 Anisotropic cellulose-based aerogel Compressible, 80% 9.79 Chloroform Gasoline 10000 5200 321 Carbon aerogel - 48 Diesel Gasoline Chloroform Pump Oil Ethylene Glycol Corn Oil 2700 2400 4900 3000 3500 2700 322 Anisotropic cellulose-graphene aerogel Compressible, 90% 5.9 Chloroform Gasoline 18500 10000 323 Double reduced GO aerogel Compressible, 90% 3.12 Motor Oil Fresh Motor Oil Used Gasoline Vacuum Oil Silicone Oil Ethylene Glycol Chloroform Diesel Oil 1-Butanol Food Oil 34500±2291 20146±1803 20750±3135 20449±615 20200±1487 30004±2356 46604±2123 26676±3555 16752±919 29867±3731 This Study Abbreviations: Graphene oxide (GO), polyvinyl alcohol (PVA), kapok fiber (KF), sodium alginate (SA), polylactic acid (PLA), cellulose nanofiber (CNF), nanofibrillated cellulose (NFC), stearic acid chloride (SAC), carbon nanofiber (CN), polyimide (PI), carbon nanotube (CNT), polyethylene terephthalate (PET), biomass-derived banana peel waste paper (BPWP), polystyrene (PS), sodium alginate (SA), nanoparticles (NPs), micro fibrillated cellulose (MFC), carbon fiber (CF), polyvinylidene fluoride (PVDF), reduced graphene oxide (rGO), multi-walled carbon nanotube (MWCNT), polydimethylsiloxane (PDMS), white bamboo fibril (WBF). 5.2.3. Filamentous aerogels piezoresistive capability The flexible nature of the developed filamentous aerogels combined with their electrical conductivity renders them a promising building block for manufacturing piezoresistive senor toward human motion monitoring. Accordingly, the thermally rGO-CNF aerogel was devised as a piezoresistive sensor (Figure 5.5 (a)), and its current response was recorded under different compressive strains (Figure 5.5 (b)). Upon increasing the compressive forces to the devised piezoresistive sensor, the interconnected conductive filaments of rGO-CNF aerogel contact with 124 each other in micro- and macro-scales, causing a significant increase in the conductance of the framework owing to the generation of new conductive pathways. Further increase of the compressive strain to 80% boosted the face-to-face contact between the adjacent conductive domains, improving the current response of the motion monitoring device. The practicality of the devised system was examined by measuring the response-recovery time (Figure 5.5 (c-d)) and sensitivity (𝑆 = ∆𝐼 𝐼0⁄ ∆𝑃⁄ ) (Figure 5.5 (e)). The outcome of assessments revealed a proper response-recovery time of 525ms-350ms and sensitivities of 24.514 kPa-1 and 0.567 kPa-1 at low and high compression forces 324, 325. Such rapid response-recovery time combined with tunable sensitivity made the devised piezoresistive sensor a versatile detector to monitor low- and large-scale body movements. The devised piezoresistive sensor demonstrated great capability in sensitive touch sensing, enabling the measurement of touch strength and frequency by assessing the current responses (Figure 5.5 (f-g)). It also unveiled proper capability/sensitivity toward real-time human motion monitoring. In this case, the sensor exhibited a reproducible and stable current response to low-scale human motion such as swallowing (Figure 5.5 (h)) and also large-scale body movements, including contraction-relaxation biceps muscles (Figure 5.5 (i)) and knee movements (Figure 5.5 (j)). Notably, the sensor also showed proper stability after 1000 compressive touch sensing cycles, in which the baseline remained almost the same with negligible variation, highlighting the potential of the sensor as a potent backbone detector for human-machine interfaces and/or flexible electronic skins (Figure 5.5 (k)). 125 Figure 5.5. (a) Assembly of the piezoresistive sensor for human motion monitoring. (b) The cyclic piezoresistive sensing performance of rGO-CNF aerogel at different compressive strains (20-80 %). (c) Response and (d) recovery time of the assembled motion monitoring sensor. (e) Sensitivity of the developed piezoresistive sensor. (f) Touch sensing via the assembled sensitive motion monitoring sensor, and (g) the recorded signal for soft and hard touching of the sensor. (h) The recorded signal of swallowing as a subtle human body motion. Monitoring large body motion, including (i) contraction-relaxation biceps muscles and (j) knee movement. (k) The stability of the motion monitoring sensor before and after 1000 compression cycles through touching. 5.2.4. Filamentous aerogels thermal insulation and Joule-heating capability The ever-growing global demand for energy and the adverse effects of fossil fuels on the ecosystem have raised an urgent need for alternative clean energy sources. Accordingly, the energy conservation approach as the fifth largest available energy source attracted noteworthy attention, showing the opportunity to recover the energy losses into the consumption cycle. To this end, effective insulators, as one the essential tools of energy preservation, play a substantial role in 126 critical infrastructures like petrochemical industries, aerospace, buildings and home appliances, transportation, and medical facilities 326. To this end, the generated multi-scale porous ultra-lightweight hierarchical aerogels with controllable micro- and macro-scale porosities can be effectively used for thermal insulation or energy preservation. Drawing on the abundant controllable micro- and macro-scale porosities, aligned micro-scale porous channels within the filaments, and electrical conductivity of the developed filamentous aerogels made them potent thermal insulators and prompt on/off thermal switchers or electric heaters. As proof of thermal insulation, the thermally reduced rGO-CNF aerogel (4 mm thick) is placed on a heating plate at 110 °C, and the dynamic temperature change is monitored via the thermal infrared camera (Figure 5.6 (a)). As evidenced in Figure 5.6 (b), the recorded temperature gradient distribution of the rGO-CNF aerogel showcased an average temperature of 45.53 °C after 60 seconds and remained nearly unchanged after 60 minutes (~46.21 °C). Likewise, the aerogel was used to block the generated thermal radiation via a 250 W incandescent heat lamp bulb. Accordingly, when aerogel was placed 30 cm, 20 cm, and 10 cm away from the lamp bulb with a temperature of about 280 °C˂, the bulb facing side of the rGO-CNF aerogel showed a temperature of 32, 39, and 54 °C, respectively, after 60 s and thence reached equilibrium, depicting the proper performance of the aerogel toward blocking the infrared radiation (Figure 5.6 (c) and (d)). The developed programmable aerogels also revealed favourable capability in maintaining body temperature (Figure 5.7) by avoiding heat transfer, which has great potential in insulative jackets. Further details about the thermal insulation character of the aerogels before and after the reduction process can be seen in Figure 5.8, revealing the positive impact of the reduction process on the thermal insulation character of aerogels. 127 The potent thermal insulation capability of filamentous aerogels stems from their multi-scale porosities, enhancing the heat-dissipating free spaces and interfacial thermal resistance, thereby lowering the contribution of the solid phase to thermal conductivity upon phonon scattering at the interfaces. Accordingly, the phonon scattering at solid-gas and solid-solid interfaces contributes to lowering the solid conduction of these aerogel constructs. Besides, the high density of thin interfaces within engineered constructs enhances the diffuse scattering, which can cause energy dissipation and decline the thermal conductivity 327. Besides the excellent heat insulation character of the developed hierarchical aerogels, they also demonstrated instant heat generation upon applying DC voltage. In this regard, the devised on/off electric heater based on the rGO-CNF aerogel (Figure 5.6 (e)) revealed instant heating and cooling characteristics, which is appealing for applications requiring quick heat dissipation to avoid heat overload at extreme conditions, such as spacecraft, cryogenic coolers, sensitive electronic equipment, and reaction tanks 328. Figure 5.6 (f-g) and Figure 5.9 showcase the instant heat generation by the aerogels upon applying voltage, capable of reaching the heating climax in only 3 s (72.4 °C at 7 V) and declining to ambient temperature after about 3 s. Such fast heat generation and dissipation performance of the aerogels, combined with their elastic resilience, ultra-lightweight and controllable features, make them versatile candidates over their brittle and poorly-structured counterparts for advanced functions and designs. 128 Figure 5.6. (a) Schematic illustration of thermal insulation character of rGO-CNF aerogel placed on a hot plate along with the temperature gradient distribution, and (b) thermal insulation property of a 4 mm thick rGO-CNF aerogel over time; the insert shows the 2D temperature gradient distribution. (c) Infrared radiation blocking capability of a 4 mm thick rGO-CNF aerogel 30 cm, 20 cm, and 10 cm far from an incandescent heat lamp bulb. (d) The 2D temperature gradient distribution of the thermal radiation source and rGO-CNF aerogel. (e) Schematic illustration of the on/off heat generator made of rGO-CNF, (f) change of the induced temperature by the rGO-CNF aerogel upon changing the applied DC voltage, and (g) 3D temperature gradient distribution of the rGO-CNF aerogel upon switching on (4V DC) and switching off after 3s. Figure 5.7. The capability of the reduced GO and reduced GO-CNF aerogels to maintain the body temperature. 129 Figure 5.8. The thermal insulation performance of non-reduced and reduced GO, and GO-CNF aerogels. Figure 5.9. The heat generation performance of reduced GO-CNF aerogel upon applying voltage. 130 5.3. Conclusions In this chapter, we harnessed the engineerable nature of the liquid templating approach to tailor the features of aerogels to meet the demands of advanced applications. As a demonstration of functionality, the tunability of aerogels through controlled liquid templates enabled the development of EMI shields with customizable shielding characteristics and exceptionally high specific shielding effectiveness (SSE/t) ranging from 31,739 to 39,893 dB cm2 g⁻1. The double-reduced GO aerogel achieved one of the highest recorded values for oil or organic solvent absorption, rapidly absorbing 487 times its original weight (for chloroform), significantly surpassing the oil absorption capacities of current best practices in the field. Additionally, the multi-scale porosity and conductive framework of the carbonized aerogels facilitated the creation of sensitive piezoresistive sensors with fast response/recovery times (525/350 ms). The aerogels also exhibited excellent thermal and infrared insulation properties, along with Joule heating capabilities, demonstrating instant cooling and heating performance within just 3 seconds. In summary, liquid templating through interfacial complexation represents a transformative strategy for material design, offering a revolutionary approach to enhancing performance and achieving on demand functionalities from multi-scale porous materials. 131 Chapter 6: Aerogel Electromagnetic Traps For decades, the inherently reflective nature of metallic EM shields and their induced secondary EM pollution have posed significant challenges for sensitive electronics. Despite extensive efforts to develop advanced electromagnetic (EM) shielding systems, the issue of reflection dominancy in metallic substrates remains unresolved. In this chapter, I leverage the engineerable nature of interfacially driven filamentous aerogels to create anti-reflection aerogels capable of mitigating incident EM waves through absorption-dominant mechanisms while suppressing surface reflections from highly conductive metallic substrates. To achieve this, I introduced the concept of “aerogel electromagnetic traps”, which manufacture multi-scale porous filamentous aerogels with numerous interfaces and enhanced EM wave dissipation parameters. By pairing metallic shields with ultra-lightweight (density of 3.12–3.40 mg cm⁻3) and elastic anti-reflection aerogels, the shielding mechanism was transformed from reflection-dominant (reflectance > 0.8) to absorption-dominant (absorbance > 0.7), as the EM waves were effectively trapped within the aerogel. The aerogels' engineerable lossy medium, characterized by a multi-scale porous structure, combined dielectric and conduction losses to dissipate EM waves while significantly minimizing reflections. Notably, reducing the diameter of the aerogel filaments further enhanced absorbance, establishing the material as a highly effective dissipating medium for EM waves. Pairing metallic substrates with these filamentous aerogel EM traps resulted in an exceptionally efficient absorption-dominant shielding system, achieving absorbance levels between 0.70 and 0.81. This system demonstrated a shielding effectiveness of 53–89 dB within the X-band frequency range. This innovative solution addresses the persistent challenge of reflective behavior in metallic substrates, effectively mitigating induced EM reflections and advancing the capabilities of EM shielding technology. 132 6.1. Introduction Electromagnetic (EM) waves have been foundational to the evolution of human civilization's communication and cutting-edge technologies, revolutionizing sectors like aviation, education, entertainment, and therapeutics.110 The proliferating usage of EM waves in communication and portable electronic devices has caused an increasing rate of EM interference (EMI) or EM pollution, obstructing the proper performance of sensitive electronics and adversely affecting biological entities.329 Since identifying the adverse effect of EM pollution on electronic systems, many types of superconductive metallic shields have been used to mitigate the impact of EM waves.65, 330 Despite the high shielding effectiveness of metallic shields, their reflection-dominant shielding mechanism and the associated secondary EM pollution restrict their applicability.110 The induced reflections as a result of enforced oscillation of free-charge carriers on the surface of highly conductive metallic substrates cause a scattered field in the form of reflection that is as harmful as the incident EM waves.331 This restricted the applicability of metallic substrates and motivated scientists to fabricate alternative advanced EM waves absorbing materials such as carbonaceous nanomaterials,332 conductive polymers,222, 333 and 2D MXene nanosheets,60, 334 assembled in porous frameworks or embedded in polymeric blends.335 Despite significant advancements, numerous contemporary shielding systems still predominantly depend on reflection, posing unresolved challenges due to secondary EM pollution.110 Fabricating absorption-dominant shielding frameworks and trapping the incident or reflected EM waves require a target-oriented approach that can engineer the multi-scale porosities and enhance the EM waves dissipating factors, e.g., multiple internal scatterings and dielectric, magnetic, and conduction losses. Indeed, manipulating multi-scale porosities and EM wave dissipating factors can lead to a potent lossy medium with minimal impedance mismatching. Controlling the 133 impedance mismatching enables suppressing the primary surface reflections, allowing the penetration of EM waves into the shielding construct.329, 336 In pursuit of this objective, aerogels have emerged as promising contenders for generating absorption-dominant shielding structures, owing to their plentiful porosity and the potential for a porous, electrically conductive/magnetic hierarchical arrangement that coexists with exceptional lightness.25 Nevertheless, a common drawback among many aerogels lies in their inherent rigidity and poor structural integrity, which collectively limits their functional versatility.337 Thus far, a plethora of strategies have emerged to develop absorption-dominant shielding constructs aimed at effectively attenuating EM waves and minimizing surface reflections by addressing impedance mismatching. These strategies encompass a range of approaches, including the implementation of gradient electrical conductivity 213, the utilization of multi-layered structures featuring alternating magnetic/conductive layers 55, the generation of foams and aerogels as highly effective porous mediums 214, 338, structured Janus aerogels 111, liquid-templating aerogels generation approach 109, engineerable bridge micro-capacitance-based shielding constructs 339, hydro-, organo-, or iono-gel absorbers 336, metal-organic-framework (MOF)-based EM waves attenuating structures 340-342, and hybrid shielding constructs featuring a combination of EM waves dissipating components 343. Regardless of the advancement in these methodologies, the emphasis has primarily been on the structural aspects, neglecting the importance of blocking induced reflections from metallic parts, which are integral components of most advanced technological equipment. Despite the recent progress in developing porous EMI shielding constructs, the capability of proposed methods in generating a versatile and superior absorption-dominant shielding structure with controllable features is still limited.65, 329 Addressing this challenge passes through the art of 134 interfacial complexation, a process that facilitates the organization of functional nanoparticles at the interface of two immiscible liquids through electrostatic interaction with a ligand. This interaction results in the jamming of nanoparticles at the interface, leading to the formation of nanoparticle surfactants. These unique nanoparticle surfactants contribute to the development of a robust solid interfacial layer, preserving the three-dimensional structure of liquid constructs while mitigating potential instabilities.4 The resulting 3D-structured liquid constructs serve as templates for the generation of aerogels. The highly controllable nature of this process, combined with various adjustable parameters, allows for the deliberate engineering of templates before the freezing and lyophilization stages. This exceptional level of control in assembly and structuring through interfacial complexation empowers the manipulation of aerogel characteristics, making it possible to tailor them for highly effective absorption-dominant shielding systems.109 Herein, the challenge associated with the induced EM pollution by the metallic substrates was addressed by employing the art of interfacial complexation, allowing the engineering of shielding structures from nano-scale chemistry and micro-scale assembly of nanoparticles (NPs) to bulk manufacturing of multi-scale porous constructs.109 Leveraging the synergistic interplay between 2D graphene oxide (GO) flakes and 1D cellulose nanofiber (CNF) within liquid templates for aerogel fabrication allows increasing intra and inter-filament porosities per volume of aerogel through precise compositional and processing adjustments. This approach increases electron migration and hopping by forming conductive networks that bridge reduced GO and CNF, optimizing the material's electrical properties. This enhances the internal scattering and conduction loss, intensifies the EM waves dissipating factors, and as a result, leads to an absorption-dominant shield with controlled surface reflections. At the same time, such synergy enhances the structural integrity and elastic resilience of aerogels, making them a potent mechanically robust porous 135 medium as a barrier against the induced reflections of other reflective substrates, e.g., highly metallic substrates. Employing the concept of interfacial complexation, we addressed a potential drawback of reflection-dominant shielding systems by coining an anti-reflection aerogel termed ‘Aerogel Electromagnetic Traps.’ When paired with metallic substrates, aerogels effectively block the incident EM waves and reflections from superconductive metals such as aluminum (Al), titanium (Ti), copper (Cu), and carbon-coated aluminum (C-Al), altering their shielding mechanism to absorption-dominant. The absorption-dominant aerogel-metal shields showed total shielding effectiveness (SET) and absorbance (A) of 58-89 dB and 0.70-0.81, respectively. The presented anti-reflection concept herein could bring a vast range of opportunities to resolve the traditional drawback of metallic shields and tackle the challenges of sensitive electronics. 6.2. Materials and Methods 6.2.1. Materials The materials used in this chapter are similar to those mentioned in Chapter 3 and Chapter 4. A combination of GO and CNF was used for aerogel manufacturing. The PSS-[3-(2-Aminoethyl)amino] propyl-heptaisobutyl substituted (POSS) as the ligand and hexane (97%) as the extrusion medium were supplied by Sigma-Aldrich. 6.2.2. Methods 6.2.2.1. Nanomaterials synthesis The detailed recipes and characterization of used nanomaterials, including GO and CNF, are provided in Chapter 3. 136 6.2.2.2. Aerogel production The aerogels were produced by lyophilizing the frozen liquid templates. Accordingly, first, the inks were prepared with the desired concentrations and composition. As such, the GO and GO:CNF (1:1 weight ratio) inks were prepared at 0.5 and 1 wt% concentrations upon mixing the proper amount of GO and/or CNF, followed by 3 h stirring and 10 min bath sonication. The inks were then loaded in a syringe equipped with the desired needle size and placed in an extrusion printing machine supported by an automatic pressure adjustment unit (Allevi 2 3D bioprinter). The liquid templates were prepared upon injection of the uniformly dispersed inks into the extrusion medium composed of 1 wt% POSS within the hexane at the pressure of 10-15 psi. Upon the injection of ink into the POSS-hexane domain, the POSS molecules diffuse into the interface and electrostatically interact with the deprotonated carboxylic acid functional groups of GO and/or CNF through protonation of their amine groups (-NH3+). This electrostatic bonding at the interface leads to the formation of nanoparticle surfactant (NPS), locking in the non-equilibrium shape of filamentous threads of GO or GO:CNF and avoiding their breakup into discrete droplets by suppressing the instabilities.109 Next, the formed liquid templates were frozen at -85 °C within an ultra-low temperature freezer for 24 h, then the POSS-hexane extrusion medium was decanted away, and finally, the frozen templates were lyophilized in a freeze drier (LABCONCO 4.5 L benchtop freeze dryer). This process leads to free-standing filamentous aerogels composed of core-shell filaments with a thin solid skin wrapped around a porous core. For the reduction of aerogels, neat GO and/or GO-CNF aerogels were placed in the tube furnace (Across International) and annealed at 800 °C for 1 h under Ar, leading to the formation of reduced GO and GO-CNF aerogels (rGO and rGO-CNF). The density of the aerogels before and after the reduction processes was analyzed by measuring the volume and weight of five aerogel samples 137 and reporting the average values (density: 𝜌=weight (g)/volume (cm3)). Of note, the frozen templates were washed several times with fresh hexane to remove any remnants of POSS or impurities on the surface of the samples prior to lyophilization. For assessing the shielding parameters, the liquid templates were generated with 27 (inner diameter (I.D.) 0.21 mm) and 15 (I.D. 1.372 mm) needle gauges to tune the diameter of the filaments after lyophilization. For shielding assessments, the aerogels were molded in 25 mL beakers with an inner diameter of 32.6 mm. The aerogels were generated at different thicknesses (2, 4, and 6 mm) to assess the effect of thickness on their total shielding effectiveness. 6.3. Characterization The synthesized nanomaterials and manufactured aerogels were characterized according to the protocols outlined in Chapters 3 and 4. 6.3.1. Electromagnetic shielding measurements The electromagnetic (EM) shielding characteristic of the generated aerogels was analyzed according to the guidelines provided in Chapter 5. The anti-reflection performance of the aerogels was analyzed with the same procedure while one side of the aerogels (the side opposite to the incident wave port) was covered with metallic substrates, including aluminum (Al) foil (thickness:15 µm), carbon-coated Al (C-Al) foil (thickness:15 µm), copper (Cu) foil (thickness:10 µm), Cu tape (thickness:50 µm), titanium (Ti) foil (thickness:20 µm), Ti mesh (thickness:426 µm), or Zn foil (thickness:106 µm). 6.4. Results and Discussion Anti-reflection aerogels, namely “Aerogel Electromagnetic Traps”, were produced through engineering the assembly of nanoparticles at the interface of two immiscible liquids, viz., interfacial complexation,109 via pressure-adjusted extrusion of aqueous inks (herein, GO (0.5-1 138 wt%, 5-10 mg mL-1) and GO: CNF (weight ratio 1:1, 0.5-1 wt%)) into the enriched hexane domain with POSS. Figure 6.1 (a) illustrates the method for yielding 3D-structured anti-reflection aerogels starting from (I) pressure-adjusted extrusion of the ink into the ligand (POSS)-oil (hexane) phase to form liquid templates and (II) freezing of the generated assemblies, to (III) lyophilization of liquid templates toward manufacturing (IV) multi-scale porous aerogels (Figure 6.1 (b)). The fabricated filamentous aerogels offer a multi-scale porous framework with abundant engineerable inter-filament (macro-scale) and intra-filament (micro-scale) porosities (Figure 6.1 (c) and (d)), making it an ultra-lightweight construct with densities ranging between 5.39-5.96 and 3.12-3.40 mg cm-3 at non-reduced and thermally annealed states (Figure 6.1 (e)), respectively. This offers a significant advantage for applications that require porosity, such as EMI shielding. It amplifies multiple internal scatterings of EM waves across various engineered interfaces, thereby greatly dissipating the electromagnetic waves.329 Indeed, the back-and-forth reflections between impedance-mismatched interfaces, along with the EM wave dissipating features such as dielectric and conduction losses, turn the aerogel into a formidable trap for incoming electromagnetic waves.329 As illustrated in Figures 6.1 (c) and (d), the bulk aerogels consisted of abundant entangled core-shell filaments that formed a well-defined 3D structure. The aerogel’s core-shell filaments comprised a solid, thin tubular skin made of nanoparticle surfactants and a porous core derived from the hierarchical arrangement of reduced GO (rGO) flakes integrated with carbonized CNF (rGO-CNF). The nanoparticle surfactants are the product of the electrostatic interaction of nanoparticles and ligands (POSS) at the interface of the two immiscible liquids (water/hexane), preserving the non-equilibrium shape of liquid filaments by overcoming the instabilities.109 139 Figure 6.1. (a) Yielding free-standing filamentous aerogels through interfacial complexation; (I) pressure-adjusted extrusion of either GO or GO:CNF ink into the POSS-hexane domain to generate liquid templates, (II) freezing of the formed filamentous liquid template at -85 °C, (III) lyophilization of the frozen assemblies, and (IV) formation of 3D-structured aerogels. (b) Ultra-lightweight GO aerogel on a light leaf of a daffodil; scale bar is equal to ~ 13.39 mm, of note this image is taken by a digital camera and the scale bar is approximate. FESEM images of (c) rGO and (d) rGO-CNF aerogels; sub-parts showing (I) bulk aerogel construct, (II) macro-scale porosities between filaments (inter-filament porosities), and (III) micro-scale porosities within the filaments (intra-filament porosities); scale bars correspond to (I) 2 mm, (II) 1 mm, and (III) 100 µm. (e) The density of the aerogels before and after the thermal annealing (800 °C, 1 h under Ar). (f) The stress-strain curve of rGO-CNF aerogels at different compressive strains, i.e., 20 to 90 %, with six compression cycles at each strain. FESEM images of the 3D-structured filamentous GO-CNF aerogels extruded by needles with gauge numbers (f) 15 (inner diameter (I.D.) of 1.37 mm) and (g) 27 (I.D. of 0.21 mm). Scale bars are equal to (f & g) (I) 2 mm and (II) 500 µm. 140 Anti-reflection aerogels were generated through the interfacial complexation, allowing tunning of their structural features, spatial arrangement, and composition to yield on demand liquid templates.109 The 3D-structured filamentous aerogels’ fabrication process starts from the liquid templating of low-concentration inks, i.e., GO (0.5-1 wt%, 5-10 mg mL-1) and GO:CNF (weight ratio 1:1, 0.5-1 wt%), in the POSS-hexane domain. Upon pressure-adjusted extrusion of the inks into the POSS-hexane, a tubular liquid thread will be formed as a result of pH-dependent electrostatic interaction between the nanoparticles and ligands at the interface, preserving the liquid thread’s shape in a non-equilibrium form by overcoming the applied pressure gradients and Plateau-Rayleigh instabilities. Accordingly, upon extrusion of the ink through the nozzle with an adjustable gauge number, the POSS molecules promptly assemble at the interface, generating a set of positively charged POSS-NH3+ assemblies, declining the interfacial tension and overcoming the instabilities. This allows the diffusion and subsequent assembly of GO at the interface through electrostatic interaction between its deprotonated carboxylic acid groups and ligand’s (POSS) protonated amine groups.4 This electrostatic interaction leads to the generation of hybrid nanoparticle surfactant assemblies and the jamming of nanoparticles, preserving the integrity of formed liquid templates through a solid-like skin around the liquid thread.25 Freezing the formed liquid template at -85 °C for 24 h and the sublimation of the ice crystals through lyophilization forms free-standing filamentous aerogels. The extrusion of the aquatic inks in the POSS-hexane domain is demonstrated in Figures 6.2 (a) and (b), showing the formation of filamentous liquid template out of (c) GO and (d) GO:CNF inks. The structured liquid templates ((Figure 6.2 (c) and (d)) provide a scaffold for the fabrication of ultra-lightweight aerogels. 141 Figure 6.2. (a-d) Extrusion of the (a) GO (10 mg mL-1) and (b) GO:CNF (1:1 weight ratio, 10 mg mL-1) inks into the POSS-hexane medium. Formation of liquid constructs made of (c) GO and (d) GO:CNF inks as a template for aerogel production. Scale bars are equal to (a) ~ 11.31 mm, (b) ~ 11.62 mm, (c) ~ 7.13 mm, and zoom area ~ 2.79 mm, (d) ~ 7.35 mm, and zoom area ~ 3.70 mm. The images demonstrated in parts (a) to (d) were taken by a digital camera, and their scale bars are approximate. Minimization of the interfacial tension by the formed nanoparticle surfactant complexes at the liquid-liquid interface is the key to interfacial complexation and the formation of non-equilibrium-shaped filamentous liquid threads. The interfacial tension of the generated inks was measured via pendant drop tensiometry. Accordingly, the extrusion of the GO ink (1 mg mL-1) into the hexane-containing POSS molecules declined the interfacial tension from around 49 mN/m for the neat hexane-water system 7, 138 to 1.90 mN/m (Figure 6.3). This implies the capability of the formed nanoparticle surfactant assemblies to minimize the interfacial tension toward preserving the filamentous shape of liquid templates and overcoming instabilities. This strengthening role of nanoparticle surfactants stems from the formation of a solid-like robust skin around the tubular liquid threads that could withstand the applied pressure gradients. 142 Figure 6.3. Dynamic interfacial tension of 1 mg mL-1 GO ink against the hexane-POSS medium. The injection of the aqueous ink containing 1 mg mL-1 GO:CNF (1:1 weight ratio) into the pure non-polar hexane led to an interfacial tension of 38.97 mN/m. Whereas, the addition of POSS to the non-polar medium declined the interfacial tension to 4.48 mN/m, enabling liquid templating (Figure 6.4 (a) & (b)). These outcomes, along with the contraction of pendant drop of GO:CNF (1 mg mL-1) ink in the hexane domain without POSS molecules, clearly revealed the inability of nanoparticles to jam at the interface (Figure 6.5). This implies the beneficial role of POSS molecules in interfacial complexation and fast diffusion toward the interface, causing the jamming of nanoparticles and generating a robust solid skin at the interface of two immiscible liquids.7, 40 The generated solid skin around the liquid thread was visualized via the contraction of the pendant drop upon injection of the aqueous GO (Figure 6.4 (c)) or GO:CNF (Figure 6.4 (d)) inks into the non-polar hexane domain containing 1 mg mL-1 POSS. As illustrated, decreasing the droplet volume leads to a decline in the interfacial areas, imposing compressive forces on the formed nanoparticle surfactant assemblies at the interface. This process was visualized as a result of wrinkles formation during the contraction of pendant droplets. Notably, the observed wrinkles indicate the proper positioning of GO or GO:CNF by the POSS molecules at the interface that causes resilient thin interfacial films as a result of the overlapping of formed assemblies. This 143 matter paves the way for fabricating green filamentous aerogels by embedding naturally harnessed fibrillated nanocellulose into the final structure. Figure 6.4. (a) Dynamic interfacial tension of the GO:CNF ink before and after the addition of POSS molecules as ligands. (b) The average interfacial tension of the GO:CNF ink against the hexane domain with and without POSS molecules. Contraction test of 1 mg mL-1 (c) GO and (d) GO:CNF ink in the extrusion medium (1 mg mL-1 POSS in hexane); the formation of the wrinkles around the droplets indicates the generation of robust assemblies at the interface capable of withstanding the applied forces and overcome the instabilities. This enables the liquid threads to preserve their integrity in a non-equilibrium filamentous form. Figure 6.5. Contraction of pendant drop related to 1 mg mL-1 GO:CNF ink (1:1 ratio) against pure hexane without POSS. The rGO-CNF aerogel showcases superb reversible compressibility, capable of undergoing 90% compressive strain and recovering its shape quickly after force release because of its high elastic resilience (Figure 6.1 (f)). Such excellent mechanical integrity roots from the unique core-shell morphology of aerogel’s filaments, capable of withstanding high compressive strains.109 The 144 versatility and swift shape recovery, combined with the adaptable nature of the process, make these developed aerogels highly manageable, positioning them ideally for advanced applications. Indeed, many aerogels exhibit inadequate mechanical performance, constraining their use in various applications. Furthermore, adjusting the gauge number of the injection needle, transitioning from 15 (inner diameter (I.D.) of 1.37 mm) to 27 (I.D. of 0.21 mm), results in a shift in the average filament diameter from 491±34 µm to 169±19 µm following lyophilization of the liquid templates. This alteration amplifies interacting interfaces and multi-scale porosities per volume within the aerogel (see Figure 6.1 (g and h) and Figure 6.6). Consequently, there is an increase in the number of porosities and spacings between filaments, facilitating the back-and-forth reflections of EM waves between interfaces and enhancing energy dissipation. Figure 6.6. The average diameter of GO-CNF aerogels prepared via an injection needle with a gauge number of (a) 15 and (b) 27. Additionally, increasing the concentration of the GO:CNF ink (maintaining a 1:1 weight ratio) from 5 mg mL-1 to 10 mg mL-1 significantly enhances the micro-scale porosities per volume within the filament and reduces the average pore size from 58.01±17.55 to 41.13±15.47 (Figure 6.7). This 145 demonstrates the tunable nature of the approach in engineering multi-scale porosities within the aerogels, thereby bolstering the trapping and dissipation of EM waves across numerous interfaces. This holds significant potential for applications like EM shielding. The EM waves are trapped amidst the induced porosities, leading to a sequential of reflections between the filaments (macro-scale porosities) and further internal reflections within the filament's porous core (micro-scale porosities), effectively converting the EM waves into heat. Figure 6.7. Pore size distribution assessment of the samples via FESEM analysis; the FESEM images of GO-CNF aerogels composed of (a) 5 mg mL-1 and (b) 10 mg mL-1 GO:CNF (1:1 weight ratio) at different zooms (I) 200x, (II) 300x, and (III) 400x. The pore size distribution and average pore size of the GO-CNF aerogel consisted of (c) 5 mg mL-1 and (d) 10 mg mL-1 GO:CNF (1:1 weight ratio), each obtained from the assessment of various spots of three different samples. The FESEM images showcase an obvious rise in the concentration of porosities per volume of the aerogel and a notable decline in the average pore size and pore size distribution upon an increase in the concentration of GO:CNF ink. Proof of GO and CNF integration in the formed hierarchical porous framework was provided through supporting X-ray diffraction (XRD) and micro-Raman spectroscopy, before and after reduction. The assessment outcomes confirmed the assembly of nanoparticles in the hierarchical 146 arrangement and restoration of the conductive carbonaceous pathway. The XRD analysis was performed via parallel beam technique, using a polycapillary collimating optic to assess the hierarchal structure of the aerogel framework. As shown in Figure 6.8, the X-ray diffractogram of GO aerogel showed a well-defined sharp 2Ѳ peak at 10.7°, corresponding to the interlayer spacing (d-spacing) of 8.2 Å attributed to the (001) crystalline plane of GO. This increase in the d-spacing compared with neat graphite (3.4 Å) arises from formed oxygen-based functional groups on the GO.144 The other broad peak at 2Ѳ of 25.2°, attributed to the d-spacing of 3.5 Å, appeared as a result of GO flakes stacking in the aerogel framework.145 Upon thermal annealing of the GO aerogel at 800 °C under Ar for 1 h, the peak of rGO aerogel shifted to 2Ѳ of 25.9° corresponding to the d-spacing of 3.4 Å. This interlayer spacing matches the d-spacing of graphite, showcasing the removal of the oxygen-based functional groups and restoration of the carbonaceous structure through graphitization. Such treatment restores the conjugation of the sp2 regions and leads to well-oriented stacking arrangements among the graphene flakes.144, 146 The X-ray diffractogram of GO-CNF aerogel also demonstrated a hybrid aerogel framework composed of GO and fibrillated nanocellulose by showcasing the main fingerprint peaks of GO and CNF. Correspondingly, the sharp peak at 2Ѳ of 10.6° originated from the assembled GO flakes in the framework, attributed to the d-spacing of 8.3 Å. Whereas the (002) crystalline plane of native cellulose (JCPDS 03-0289) appeared at 2Ѳ of 22.3, corresponding to the interlayer spacing of 3.9 Å. The reduction of GO-CNF (rGO-CNF) aerogel at 800 °C under Ar completely changed its X-ray diffractogram, showcasing a broad peak at 2Ѳ of 25.7° attributed to the d-spacing of 3.4 Å. This outcome vividly illuminates the removal of the oxygen-based functional groups and the formation of a 3D stacked arrangement between the fibrillated nanocellulose and graphene flakes. 147 Figure 6.8. X-ray diffractograms of aerogels before and after thermal annealing. Reprinted with permission from reference 109 under Creative Commons CC BY-NC 3.0 license. Of note, the baseline of the X-ray diffractograms was removed via further post-processing. The micro-Raman spectroscopy showcased two well-defined peaks for all reduced and non-reduced aerogels between regions 1334-1348 cm-1 and 1585-1598 cm-1, corresponding to the D-band and G-band of either GO or thermally annealed GO, assembled within the 3D hierarchical framework (Figure 6.9). As demonstrated, the GO aerogel showed ID/IG of 0.98, which elevated to 1.03 after thermal annealing, indicating a slight rise in the structural defects as a result of functional group detachment. However, the GO-CNF aerogels showcased lower defect rates than the GO or rGO aerogels, revealing an ID/IG ratio of 0.85 and 0.93 before and after thermal annealing. The above outcomes support the outcomes of X-ray diffractograms and confirm the existence of either GO or rGO in the hierarchical framework of aerogels. 148 Figure 6.9. Micro-Raman spectroscopy results of aerogels before and after thermal annealing. The electrical conductivity of the aerogel, as an essential character of any shield, was increased from 11.43 S/m for rGO aerogel to 35.63 S/m for carbonized rGO-CNF aerogel (Figure 6.10 (a)). Importantly, maintaining the aerogels' electrical conductivity at a controlled level can reduce the initial surface reflections. This allows the EM waves to penetrate and become effectively trapped within the shield.110 149 Figure 6.10. (a) The electrical conductivity of the rGO and rGO-CNF aerogels. (b) The EMI shielding and (c) shielding coefficients of rGO-CNF aerogels at different ink concentrations (0.5 and 1 wt%) and thicknesses (2-6 mm). (d) The frequency-dependant EMI shielding of rGO-CNF aerogels over the X-band frequency range (8.2-12.4 GHz). Comparing small-sized and large-sized filament aerogels, including (e) EMI shielding and shielding parameters, (f) frequency-dependant EMI shielding over the X-band frequency range, and (g) shielding coefficients. (h) The absorbance (A) of the rGO-CNF aerogel (1 wt% ink, gauge 27, i.e., small-sized filaments) at different thicknesses compared with previously developed foams and aerogels; the corresponding data can be seen in Table 6.1. (i) The shielding mechanism of rGO-CNF aerogels with (I) large and (II) small filaments. As illustrated, declining the diameter of the filament in rGO-CNF aerogels increases the number of interfaces and porosities per volume of the aerogel, increasing the equivalent impedance and thereby minimizing the surface reflection. This alters the nature of the shield from dominant reflection to absorption. Figures 6.10 (b-c) and Figures 6.11-6.12 demonstrate the shielding effectiveness and shielding coefficients of the rGO-CNF aerogels at different ink concentrations (0.5 and 1 wt%) and thicknesses (2, 4, and 6 mm). As evidenced, the rGO-CNF aerogels prepared with an ink 150 concentration of 0.5 wt%, extruded with a gauge 27 needle, showcased a SET ranging from 19 dB to 31 dB for aerogels with 2 to 6 mm thicknesses with an absorption-dominant shielding characteristic (absorbance of 0.58-0.69 and absorption loss (SEA) of 16.92-29.76). Similarly, a slight increase in the ink concentration to 1 wt% considerably boosted the SET to 25.54-59.32 dB for aerogels with thicknesses 2 to 6 mm with a stronger absorption-dominant characteristic (absorbance of 0.68-0.73 and SEA of 23.91-57.94). Additionally, the frequency-dependent EM shielding (Figure 6.10 (d)) showed a stable EMI shielding over the whole X-band frequency range (8.2-12.4 GHz), indicating the strong shielding performance of the filamentous aerogels. Interestingly, experimental assessments revealed that tuning the diameter of the filamentous aerogels by changing the needle gauge during extrusion could alter the shielding characteristic of the aerogels. In this regard, two different types of filamentous aerogels were prepared with needle gauges of 27 and 15, denoted as small and large filaments. Both aerogels with small and large filaments exhibit strong SET values of 59.32 and 63.39 dB (Figure 6.10 (e) and Figure 6.13), respectively, with a nearly stable uprising frequency-dependant EMI SE over the whole X-band frequency range (Figure 6.10 (f)). The aerogel with a smaller filament size (injection needle gauge 27) showed an absorption-dominant shielding behavior (absorbance of 0.73 and SEA of 57.94 dB), while increasing the filament size (injection needle gauge 15) altered the shielding character to reflection-dominant (absorbance of 0.40 and SEA of 59.47 dB) (Figure 6.10 (g)). This discrepancy arises due to the presence of broader impedance mismatched surfaces in aerogel, characterized by larger filaments and significantly fewer porosities. This configuration leads to increased scattering of EM waves, primarily in the form of reflection. The underlying mechanism involves the enforced oscillation of free charge carriers on the shield's surface, which prevents the penetration of EM waves into the aerogel. Consequently, this configuration hinders the further dissipation of these 151 waves.110 Whereas, in aerogel with smaller filaments, soaring in the volume of porosities increases the equivalent impedance and declines the surface reflection.64 This allows the EM waves to penetrate the shield and be dissipated when facing numerous interfaces in the porous core of the aerogel filaments. Of note, a porous material's equivalent impedance ranges between its components' impedance, i.e., free space and conductive scaffold. Devising a higher equivalent impedance, i.e., a closer resemblance to the impedance of free space (377 Ω), allows EM waves to penetrate the structure with reduced reflections.64 Moreover, thanks to lightness, abundant porosities, and high Ohmic loss, both aerogels with small and large filaments offer remarkable specific shielding effectiveness (SSE/t) of 35,218 and 32,691 dB cm2 g-1, respectively. Compared with the recent practices in the field (Figure 6.10 (h) and Table 6.1), the small filament aerogels can offer high shielding effectiveness at one of the lowest ink concentrations (0.5-1 wt%) or densities with an absorption-dominant shielding character. The exceptional shielding performance of the filamentous aerogels can be attributed to their distinct multi-scale porous architecture. As depicted in Figure 6.10 (i), when EM waves strike the aerogel, a series of interactions occur: a portion of the incident EM waves reflect off the aerogel surface in the form of a scattered field, which was minimized by increasing the equivalent impedance. This allows penetration into the shield where the EM waves trap and the main dissipation occurs. Reflections recur between the filaments because of their macro-scale porosity. This is accompanied by scattering at the interface of the solid exterior and porous core, with additional internal scattering taking place within the filaments' micro-scale porosities. These interactions result in a significant reduction of the EM waves' energy. As a result, the energy from these waves is converted into heat due to the high kinetic energy of mobile charge carriers vibrating at elevated frequencies,64 leading to highly effective shielding with a predominantly absorptive 152 characteristic. It's noteworthy that, as per the data gathered, the diameter of the filaments is instrumental in this absorption-dominant shielding. Figure 6.11. EMI SE characteristic of rGO-CNF aerogel prepared with 0.5 wt% ink at (a) 2 mm, (b) 4 mm, and (c) 6 mm thicknesses. Figure 6.12. EMI SE characteristic of rGO-CNF aerogel prepared with 1 wt% ink at (a) 2 mm, (b) 4 mm, and (c) 6 mm thicknesses. Figure 6.13. EMI SE characteristic of 6 mm thick rGO-CNF aerogel prepared with 1 wt% ink with (a) small and (b) large filaments. 153 Table 6.1. EMI shielding performance of the rGO-CNF aerogel with large and small filaments compared to recently developed porous constructs. Sample Thickness (mm) EMI SE (dB) SER (dB) R A Ref. Hybrid core-shell CNT-graphene foam 1.6 38.4 3.9 0.59 0.41 193 MWCNTs-WPU foam 2.3 50.5 ~9 ~0.89 ~0.11 194 CNT sponge-epoxy 2 44 5 ~0.68 ~0.32 196 Hybrid AgNWs-carbon sponge 3 70.1 ~11 ~0.91 ~0.09 203 CNTs-rGO foam 2 31.2 5.9 0.74 0.26 206 rGO foam 0.9 42.3 10 0.9 0.1 207 Ti2CTx-PVA foam 5 28 2 0.37 0.63 210 Ti3C2Tx-PEDOT:PSS aerogels 5 28 3 0.5 0.5 214 Honeycomb-structured porous graphene-AgNWs 0.0483 61.8 ~14.5 ~0.96 ~0.04 226 AgNWs-nanocellulose aerogels 2 70.5 ~17 ~0.98 ~0.02 78 Hybrid CNTs-ANFs aerogel 0.568 54.4 ~8 ~0.84 ~0.16 183 Core-shell Cu NWs-graphene aerogel 5 43.7 2.86 ~0.48 ~0.52 233 Core-shell compressed Cu NWs-graphene aerogel 5 31.28 4.11 ~0.61 ~0.39 233 Ti3C2Tx-rGO aerogel 2 56.4 5.7 0.73 0.27 173 Carbonized wood-Ni-CNTs - 48.2 2.8 ~0.47 ~0.53 242 Graphene-boron nitride nanoribbons aerogel 2 70 ~12 ~0.8 ~0.2 344 rGO-CNF aerogel 2 25.54 1.62 0.30 0.68 This Study rGO-CNF aerogel 4 45.62 1.43 0.27 0.72 rGO-CNF aerogel 6 59.32 1.38 0.26 0.73 Abbreviations: Carbon nanotube (CNT), multi-walled carbon nanotube (MWCNT), water‐borne polyurethane (WPU), silver nanowires (AgNWs), reduced graphene oxide (rGO), polyvinyl alcohol (PVA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), nanowires (NWs). These devloped aerogel EM traps with minimized surface reflection and a multi-scale porous lossy medium for EM waves can be used as a potent barrier against the induced secondary EM pollution of metallic shields or even the metallic parts of sensitive electronics.110 When paired with metallic substrates, these aerogels are capable of shifting the shielding mechanism of metals from predominantly reflective (R˃0.8) to notably absorptive (A˃0.7). Figure 6.14 (a) showcases the anti-reflection character of rGO-CNF aerogels when paired with metallic substrates (Figure 6.14 (a) I-II). The anti-reflection property of the produced aerogels originates from their potent lossy medium coupled with a controlled electrical conductivity. Choosing a finite electrical conductivity ensures that EM waves can penetrate the aerogel's EM trap with reduced surface reflections. 154 However, an unchecked increase in electrical conductivity can give rise to induced reflections, as this is primarily a surface phenomenon. Figure 6.14. (a) Aerogel EM trap’s mechanism of action, including (I) their pairing with superconductive metallic substrates, (II) blocking the induced reflections, i.e., secondary EM pollution, of metallic substrates and multiple reflections among inter-filament porosities, (III) interaction of EM waves with intra-filament porosities, including the 155 multiple reflections between the skin and core of the core-shell filaments and multiple internal reflections within the porosity of the tubular porous core of aerogel’s filaments, (IV) interfacial and/or dipole polarization losses, and (V) conduction loss as a result of electron migration and hopping. The golden rods in parts IV and V represent the CNF, while blue and red spherics show positive and negative charges. (b) The EMI SE, and (c) the shielding coefficients of 6 mm thick rGO-CNF aerogels (1 wt%, gauge 27) with and without thin metallic foils/tape cover. EMI SE of the (d) rGO-CNF aerogels without any back cover and with (e) (I) 15 µm Al foil, (II) 15 µm carbon coated Al foil (C-Al foil), (III) 10 µm Cu foil, (IV) 50 µm Cu tape, and (V) 20 µm Ti foil, (VI) 426 µm Ti mesh, and (VII) 106 µm Zn foil within the X-band frequency range. Furthermore, the vast array of interfaces and porosities in multi-scale porous aerogels, such as those between filaments, between the filament's outer layer and its porous core, and within the micro-scale porosities of the tubular core, greatly enhance multiple reflections and internal scatterings (as depicted in Figure 6.14 (a) parts II-III). This significantly contributes to creating a powerful medium for trapping and attenuating EM waves. By optimizing these multi-scale porosities and amplifying both interfacial/dipole polarization and conduction loss, one can more effectively dissipate incoming EM waves, capitalizing on the cumulative effect of multiple scatterings.345-347 Furthermore, the stacking of rGO flakes and their intimate interactions with carbonized CNFs or other rGO flakes result in interfacial polarization at contact sites plus dipole polarization at localized defective areas when exposed to alternating electromagnetic fields, enhancing the loss of EM waves, as illustrated in Figure 6.14 (a) IV. In this context, the one-dimensional (1D) carbonized CNFs serve as connective bridges to the two-dimensional (2D) rGO flakes. This synergy creates a conductive network facilitating electron migration and hopping, which in turn contributes to conduction losses and helps dissipate the energy of the EM waves, as depicted in Figure 6.14 (a) V.348 Notably, the defective sites in the stacked rGO sheets improves polarization loss, benefiting the dissipation of EM waves.349, 350 Importantly, when the EM waves strike the metallic substrate at the back of the aerogel EM trap, the EM waves reflect back and dissipate in 156 the lossy medium of the aerogel trap. This blocks the induced secondary EM pollution of metallic substrates as one of the most important challenges of shielding science and sensitive electronics. As a proof of concept, a 6 mm thick rGO-CNF aerogel (1 wt%, gauge 27) was paired with Al foil (thickness (t):15 µm), carbon-coated Al (C-Al) foil (t:15 µm), Cu foil (t:10 µm), Cu tape (t:50 µm), Ti foil (t:20 µm), Ti mesh (t:426 µm), and Zn foil (t:106 µm), and the EMI shielding parameters and shielding coefficients were recorded. All the employed thin metallic substrates standalone showcased a reflection-dominant shielding character with reflectance (R) and SET of 0.88-0.98 and 30.08-48.25 dB, respectively (Figure 6.15-6.16 and Table 6.2). Upon pairing the metallic substrates with anti-reflection ultra-lightweight filamentous rGO-CNF aerogel, the nature of all shielding systems changed from reflection-dominant to totally absorption-dominant with absorbance (A), SEA, and SET of 0.70-0.81, 57.98-88.11 dB, and 58.85-89.32 dB, respectively (Figure 6.14 (b-c) and Table 6.3). Additionally, the rGO-CNF aerogel (Figure 6.14 (d)) and paired metallic substrates with anti-reflection aerogel (Figure 6.14 (e)) showcased superior shielding effectiveness with significantly minimized reflection loss (SER), over the whole X-band frequency range (8.2-12.4 GHz). Figure 6.15. (a) Shielding coefficients (reflectance (R) and absorbance (A)) and (b) shielding parameters (reflection loss (SER), absorption loss (SEA), and total specific shielding (SET)) of used metallic foils, mesh, or tape. 157 Figure 6.16. EMI SE of (a) Al foil (thickness (t):15 µm), (b) carbon-coated Al (C-Al) foil (t:15 µm), (c) Cu foil (t:10 µm), (d) Cu tape (t:50 µm), (e) Ti foil (t:20 µm), (f) Ti mesh (t:426 µm), and (g) Zn foil (t:106 µm) over the X-band frequency range (8.2-12.4 GHz). Table 6.2. Shielding parameters and coefficients of metallic substrates; the recorded parameters are average of four assessments in the whole X-band frequency range (8.2-12.4 GHz). Metallic Substrate Thickness (µm) Shielding Coefficients EMI SE (dB) A R SER SEA SET Al foil 15 0.03 0.96 15.23 33.02 48.25 C-Al foil 15 0.06 0.93 12.21 31.64 43.85 Cu foil 10 0.07 0.92 11.95 24.02 35.98 Cu tape 50 0.01 0.98 17.23 28.76 46.00 Ti foil 20 0.04 0.95 13.92 27.40 41.33 Ti mesh 426 0.11 0.88 9.67 20.71 30.39 Zn foil 106 0.06 0.93 12.15 25.92 38.08 158 Table 6.3. Shielding parameters and coefficients of hybrid aerogel (6 mm thick rGO-CNF (1 wt%))-metallic substrates shielding system; the recorded parameters are average of four assessments in the whole X-band frequency range (8.2-12.4 GHz). Metallic Substrate Shielding Coefficients EMI SE (dB) A R SER SEA SET rGO-CNF Aerogel 0.71 0.28 1.46 51.61 53.07 rGO-CNF Aerogel/Al foil 0.75 0.24 1.20 88.11 89.32 rGO-CNF Aerogel/C-Al foil 0.79 0.20 0.99 84.53 85.52 rGO-CNF Aerogel/Cu foil 0.71 0.28 1.46 85.46 86.93 rGO-CNF Aerogel/Cu tape 0.73 0.26 1.36 83.39 84.76 rGO-CNF Aerogel/Ti foil 0.70 0.29 1.54 82.55 84.09 rGO-CNF Aerogel/Ti mesh 0.81 0.18 0.87 57.98 58.85 rGO-CNF Aerogel/Zn foil 0.76 0.23 1.15 72.83 73.98 The proposed “Aerogel Electromagnetic Trap” approach provides an efficient aerogel framework capable of effectively minimizing the surface reflection, dissipating the intruding EM waves in their multi-scale porous lossy medium, and blocking the induced EM pollution of metallic substrates when paired with them. This paired aerogel-metal system establishes a new benchmark in absorption-dominant shielding designs, positioning it as one of the best practices in the field (Figure 6.17 and Table 6.4). Figure 6.17. The EM shielding performance of developed anti-reflection aerogels paired with metallic substrates compared with recent practices in the field; corresponding data can be seen in Table 6.4. 159 Table 6.4. The developed hybrid aerogel-metallic substrate shields compared with the recently developed shielding systems. Shield Composition Thickness (mm) A SER (dB) EMI SE (dB) Ref. Ti3C2Tx 0.014 ~0.01 ~20 82 202 Ti3C2Tx 0.005 ~0.02 17.5 57.4 229 Ti3CNTx 0.005 ~0.02 17 49.7 229 Ti3C2Tx 0.001 ~0.04 13.5 46.1 188 Ti3C2Tx 0.02 <0.01 27 68 200 Ti3C2Tx/gelation 0.004 ~0.02 ~19.2 53.6 225 ANF-Ti3C2Tx 0.018 0.1 10.3 55.9 217 ANF-Ti3C2Tx 0.037 ~0.02 ~18 48 243 CNF-Ti3C2Tx 0.074 ~0.29 5.3 25.8 237 BC-Ti3C2Tx 0.006 0.01 17 37.3 351 Multilayer CNF-Ti3C2Tx 0.035 0.02 17.7 39.6 211 PVA foam-Ti3C2Tx 5 0.63 2 28 210 PVA-Ti3C2Tx 0.3 0.09 11 21 210 Multilayer PVA-Ti3C2Tx 0.027 0.15 8.3 44.4 215 PS-Ti3C2Tx 2 ~0.22 6.5 61.2 191 PCC-Ti3C2Tx-PVA - 0.01 19.13 70.08 198 Polyolefin- Ti3C2Tx-Graphene 1.85 mm 0.11 9.23 60.98 232 Polyimide-Ti3C2Tx Hollow microspheres - 0.005 23 85 334 Latex-SWCNT-Ti3C2Tx 1.1 ~0.02 ~19 52 192 PVDF-PANi-Ti3C2Tx 1.7 0.3 5.2 33.3 221 PEDOT:PSS-Ti3C2Tx aerogel 5 0.5 3 28 214 PEDOT:PSS-Ti3C2Tx hydrogel 0.295 0.42 3.7 51.7 222 rGO-Ti3C2Tx aerogel 2 0.27 5.7 56.4 173 CF-Ti3C2Tx 0.343 ~0.03 ~15 45.7 245 PANi-CF-Ti3C2Tx 0.55 0.26 5.7 26.5 219 PD-Ti3C2Tx 0.007 ~0.03 ~16 58.4 234 XG-Ti3C2Tx 0.012 ~0.03 ~15 40.1 228 rGO film 0.0084 ~0.16 ~8 20 190 Graphene fiber 0.0263 0.11 ~9 56 189 rGO-liquid metal 0.033 0.006 22 80 352 rGO-CNT foam 2 0.26 5.9 31.2 206 PDMS-rGO 5 0.51 2.99 26 7 rGO foam 0.9 0.1 10 42.3 207 Graphene-Fe3O4 0.25 0.16 8 24 209 Graphene-CuNWs aerogel 5 ~0.52 2.86 43.7 233 Compressed Graphene CuNWs aerogel 5 ~0.39 4.11 31.28 233 Graphite film ~0.0004 ~0.31 ~5 27.8 235 Anisotropically oriented carbon films 480 nm 0.16 7.96 21.72 195 PMMA-graphene-MWCNT 2 0.22 6.67 36 212 Multilayer WPU-rGO-Fe3O4-MWCNT 0.8 0.73 1.46 36 213 PMMA-rGO-Fe3O4 2.9 0.4 4 29.3 216 rGO-AgNWs network ~0.0001 ~0.16 8.1 35 240 rGO-(C-SiC)n (n=1, 3, and 12) 4 ~0.06 ~12 70.2 244 Graphene-CNT core-shell foam 1.6 0.41 3.9 38.4 193 WPU-MWCNTs foam 2.3 ~0.11 ~9 50.5 194 Epoxy-CNT sponge 2 ~0.32 5 44 196 Epoxy-MWCNT-Fe3O4-Ag 2 0.35 4.5 35 201 PLLA-MWCNT 1.5 0.4 4 30 204 PVDF-MWCNT 1 0.23 6.3 22.5 205 WPU-MWCNT 2.3 ~0.2 ~7.2 46.7 230 ANF-CNT hybrid aerogel 0.568 ~0.16 ~8 54.4 183 160 Shield Composition Thickness (mm) A SER (dB) EMI SE (dB) Ref. ANF-CNT 0.024 ~0.04 ~14 36 236 GTR-CNT 1 0.25 6 30 208 ANF-PVA hydrogel-AgNWs-PVA ~0.3 ~0.03 16 52 197 CNF-AgNWs aerogel 4 ~0.03 15 70 78 Leather-AgNWs 0.5 ~0.16 ~8 55 199 Carbon-AgNWs sponge 3 ~0.09 ~11 70.1 203 Porous honeycomb graphene-AgNWs 0.0483 ~0.04 ~14.5 61.8 226 AgNWs aerogel 3 ~0.01 20 109.3 353 Cu nanosheets 0.063 ~0.04 ~14 105 231 Porous 2D Cu nanosheets 0.015 0.1 10 100 231 Electroless plating Cu NPs-PU nanofiber 0.015 0.001 29.55 63.5 354 rGO-CNF Aerogel 6 0.71 1.46 53.07 This Study rGO-CNF Aerogel/Al foil 6+0.015 0.75 1.20 89.32 rGO-CNF Aerogel/C-Al foil 6+0.015 0.79 0.99 85.52 rGO-CNF Aerogel/Cu foil 6+0.010 0.71 1.46 86.93 rGO-CNF Aerogel/Cu tape 6+0.050 0.73 1.36 84.76 rGO-CNF Aerogel/Ti foil 6+0.020 0.70 1.54 84.09 rGO-CNF Aerogel/Ti mesh 6+0.426 0.81 0.87 58.85 rGO-CNF Aerogel/Zn foil 6+0.106 0.76 1.15 73.98 Abbreviations: Aramid nanofibers (ANF), cellulose nanofiber (CNF), bacterial cellulose (BC), polyvinyl alcohol (PVA), polystyrene (PS), phase change capsules (PCC), single-walled carbon nanotubes (SWCNT), poly(vinylidene fluoride) (PVDF), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), reduced graphene oxide (rGO), carbon fiber (CF), polyaniline (PANi), polydopamine (PD), xanthan gum (XG), carbon nanotube (CNT), polydimethylsiloxane (PDM), copper nanowires (CuNWs), poly (methyl methacrylate) (PMMA), multi-walled carbon nanotube (MWCNT), water‐borne polyurethane (WPU), silver nanowires (AgNWs), poly(L-lactide) (PLLA), ground tire rubber (GTR), nanoparticles (NPs), and polyurethane (PU). 6.5. Conclusions This chapter presents a versatile strategy for trapping and dissipating electromagnetic (EM) waves, termed "Aerogel Electromagnetic Traps". This approach involves utilizing liquid templates of GO:CNF ink to produce filamentous multi-scale porous aerogels. These aerogels provide a breakthrough solution to critical challenges in shielding science: i) the reflection-dominant nature of metallic or highly conductive EM shields and their induced secondary electromagnetic pollution. The key to unlocking this potential lies in the engineered porosity of the aerogel, which can be tailored across multiple scales as needed. By adjusting the porosity and filament size, we can minimize surface reflection by facilitating impedance matching and increasing the number of interfaces for dissipating EM waves. This transformation shifts the aerogel's shielding nature from 161 being predominantly reflective to absorptive. The resulting absorption-dominant shielding systems effectively trap EM waves, attenuate incident waves, and block reflections from metallic substrates. When paired with metallic substrates, these systems exhibit superior absorption-dominant (A:0.70-0.81) shielding effectiveness with a substantial SET of 58-89 dB. The pronounced anti-reflection properties of these ultra-lightweight aerogels hold promise for addressing longstanding challenges in shielding science. Our innovation opens new avenues for enhancing the efficiency of metallic shields by transitioning them to primarily operate through absorption-dominant shielding mechanisms. 162 Chapter 7: From Jammed Emulsion Gels to 3D Printable Engineerable Aerogels 3D printing ultra-lightweight porous structures using direct ink writing (DIW) while maintaining their mechanical robustness is highly challenging. This difficulty amplifies when we use low ink concentrations to create complex geometries. This chapter introduces a versatile method to address this shortfall through interfacially jammed emulsion gels. The gel emerges from the electrostatic interaction among synergized nanomaterials (graphene oxide (GO) and cellulose nanocrystals (CNCs)) in the aqueous phase and a ligand in the oil phase. This interaction leads to the jamming of nanoparticles and the creation of stable emulsion gels. Further post-jamming ionic crosslinking of formed interfacial assemblies by crosslinking with NaHCO3 dictates the emulsion gels’ rheological characteristics, enhancing the ink's viscoelastic properties for high-resolution 3D printing without interrupting the jammed assemblies. The customizable emulsion system allows control over porosity from the macro- to the micro-scale and generates complex geometries with desired compositions. By manipulating post-annealing processes and varying concentrations, it is possible to achieve aerogels that feature a remarkably low density (~2.63 mg cm-³) and adjustable mechanical robustness (elastic modulus of 0.45 MPa). Additionally, this method allows for producing aerogels with flexible or stiff characteristics as required, alongside the capability to tailor specific electromagnetic shielding effectiveness (ranging from 6791 to 19615 dB cm² g-1), showcasing the technique's versatility and engineerability. 7.1. Introduction Macroscopic 3D-structured hierarchical porous frameworks composed of functional nanomaterials have garnered significant attention due to their remarkable potential in fields such as 163 electromagnetic interference (EMI) shielding 355, sensors 111, and thermal management 356. 3D printing has emerged as a promising method for fabricating custom macrostructures with complex geometries through computer-guided 3D design 357. This technique allows precise control over the spatial arrangement of constructs using various approaches, including fused deposition modelling (FDM), stereolithography, digital light processing, and direct ink writing (DIW) 358, 359. DIW, being a practical 3D printing approach with scalability and material versatility for advanced functions and designs, relies on the rheological characteristics of the ink. Achieving an appropriate storage modulus, yield stress, and shear-thinning behavior is crucial for ensuring the ink's smooth flow through a nozzle with a pre-defined gauge number, enabling printing precision with desired shape fidelity and resolution 3. This capability is particularly advantageous for fabricating ultra-lightweight aerogels with engineerable 3D morphology. However, the 3D printing of low-concentration inks containing 1D/2D nanomaterials through DIW is still challenging due to their poor viscoelastic properties 3. While various strategies have been developed to enhance inks’ viscoelasticity, such as concentration enhancement 360, ionic crosslinking 361, template-assisted methods 362, and the addition of functional fillers 222, producing ultra-lightweight 3D-printed aerogels with a desired hierarchical arrangement and proper printing resolution at low ink concentrations remains a challenge. Emulsification through interfacial complexation emerges as a promising strategy for tuning the viscoelastic properties of inks, facilitating aerogel 3D printing at low nanomaterial concentrations 3. The electrostatic interaction between ligands and nanoparticles at the oil/water interface leads to the formation of nanoparticle surfactants (NPSs), stabilizing the emulsion due to the considerably 164 higher binding energy of NPSs than conventional surfactants, preventing droplet coalescence 4. This approach enables a broad range of nanomaterial selections for emulsification, serving as a template or 3D-printable ink for generating porous constructs with engineerable composition, porosity, and functionality 363, 364. The controllable structure of nanomaterials achieved through a synergistic process of emulsification and interfacial complexation empowers the customization of aerogel structures for targeted applications, including but not limited to electromagnetic interference (EMI) shielding, thermal insulation, and piezoresistive sensors 3, 111. This versatility becomes particularly essential when coupled with precise control over the 3D spatial arrangement, enabling the 3D printing of tunable viscoelastic inks, facilitating the creation of intricate geometries, and expanding the potential applications even further 3. Moreover, conventional aerogels often face challenges such as inadequate mechanical stability, the formation of rigid or brittle structures, and a lack of elastic resilience, limiting their applicability 365. Herein, we present an innovative emulsification approach that revolves around the strategic jamming of nanoparticles at the water/oil interface. This process yields stable emulsion gels, serving as a robust template to produce free-standing aerogels through freezing and lyophilization. The resulting assemblies are a product of the synergistic co-assembly of cellulose nanocrystals (CNCs) bio-macromolecules and graphene oxide (GO) flakes. These components electrostatically interact with ligands at the interface of oil droplets. By finely tuning the CNC concentration during emulsification, we can control the rheology of the emulsion gel and facilitate a transition from flexible free-standing aerogels to stiffer structures, exhibiting high ultimate strength at remarkably low densities. Moreover, as a highly interfacially active 2D flake, GO facilitates the jamming at the interface and improves the structural integrity of the resulting construct in synergy with CNC. Employing post-jamming ionic crosslinking significantly 165 enhanced the emulsion gel’s viscoelastic properties and, thus, 3D printing shape fidelity. This enhancement allows for the high-resolution 3D printing of the jammed emulsion gel through DIW with a desired complex architecture, allowing manufacturing aerogels with control over their 3D morphology. Subsequent thermal annealing of the aerogels (800 °C under Ar for 1 h) results in the formation of highly effective electromagnetic shielding systems with total shielding effectiveness (SET) ranging from 51.5 to 79.4 dB and 16.7 to 38.2 dB for free-standing (thickness 10 mm) and 3D-printed aerogels (thickness 1-4 mm), respectively, at different concentrations or thicknesses. This signifies a substantial advancement in generating aerogels with superior mechanical properties and tailored electromagnetic shielding capabilities through an innovative emulsification-based methodology. 7.2. Materials and Methods: 7.2.1. Materials In this part of the research, GO and CNC were used to manufacture emulsion-templated aerogels. A detailed list of used materials for the synthesis of GO is provided in Chapter 3. CNCs were supplied by CelluForce. PSS-[3-(2-aminoethyl)amino] propyl-heptaisobutyl substituted (POSS-NH2) and hexane (97%) were supplied by Sigma Aldrich and employed as ligand and non-polar medium for emulsion gel preparation, respectively. Sodium bicarbonate (NaHCO3), supplied by Sigma Aldrich, was used as the salt for secondary ionic crosslinking of CNCs. Calcofluor White Stain containing Evans Blue was purchased from Sigma Aldrich and used to stain the emulsion gels for confocal microscopy. 166 7.2.2. Methods 7.2.2.1. Nanomaterials synthesis The GO was used to fabricate the emulsion-templated aerogels. Detailed manufacturing procedures and characterization of GO can be seen in Chapter 3. 7.2.2.2. Emulsion gels and free-standing aerogels manufacturing The emulsion gels were prepared by mixing three different phases: two aqueous phases and one oil phase, leading to the formation of nanoparticle surfactants and the jamming of nanoparticles at the interface. The jamming of nanoparticles at the interface through the electrostatic interaction with the ligand forms a gel that can be used as a template for aerogel production. Accordingly, GO paste with a fixed concentration (10 mg mL-1, 1 wt%) was mixed (30 min, 400 rpm) with a CNC mixture with concentrations 1, 3, 5, and 10 wt% with a weight ratio of 1:1. Next, a mixture of hexane containing POSS-NH2 (1 mg mL-1) was added to the previous suspension with a weight ratio of 2:1 and stirred to induce jamming. Every 5 minutes, the gels were gently mixed with a spatula, followed by continuous stirring until jamming occurred and a well-defined viscous gel was obtained. The gels with the desired concentrations were poured into molds and then placed in an ultra-low temperature freezer at -85 °C for 24 h. They were subsequently freeze-dried using a 4.5 L LABCONCO benchtop freeze dryer for 48 h to yield aerogels upon lyophilization. Table 7.1 lists the aerogel concentrations, processing times, and labels. 167 Table 7.1. Prepared free-standing aerogels’ composition and tags. Aerogel Concentration (mg/mL) Processing GO Phase (In Water) CNC Phase (In Water) POSS-NH2 Phase (In Hexane) GO1 CNC1 10 10 1 NPs Jamming and gel formation, molding, 24 h freezing (-85 °C), and lyophilization (48 h). GO1 CNC3 10 30 1 GO1 CNC5 10 50 1 GO1 CNC10 10 100 1 7.2.2.3. 3D-printing of jammed emulsion gels The 3D-printable emulsion gels with proper and optimized viscoelastic properties for DIW were prepared by adding 75 mM NaHCO3 to the formed GO1 CNC10 emulsion gel. Upon adding NaHCO3, the mixture’s viscosity and viscoelastic behavior were significantly enhanced, enabling 3D printing of the ink. Correspondingly, the gels were 3D-printed on glass substrates with a pressure of 50-60 psi and a printing speed of 10-15 mm/sec with desired spatial morphology and in-fill distance of 3 mm, followed by freezing (-85°C) for 24 h and lyophilization for 48 h. 7.2.2.4. Aerogels reduction Free-standing and 3D-printed aerogels were thermally annealed in an Across International tube furnace at 800 °C for 1 h under Ar with a temperature ramp of 5 °C/min. For free-standing aerogels, the thickness was set at 10 mm, while for 3D-printed constructs, the thickness varied between 1 mm, 3 mm, and 4 mm. 7.3. Characterization The materials and aerogels characterization were carried out according to the detailed methods mentioned in Chapters 3 and 4. Dynamic interfacial tension (IFT) tests were carried out via the DSA KRÜSS Scientific drop shape analyzer model DSA25E by holding a droplet of emulsion gels or GO against the POSS-hexane domain. The jamming of nanoparticles was visualized through 168 the formation of wrinkles during the contraction of the pendant droplet. This was performed by injecting an aqueous droplet of emulsion gels or GO into hexane's non-polar domain, both with and without POSS molecules. The mechanical properties of aerogels were examined via a Z010 Zwick/Roell universal testing machine equipped with a 200 N load cell. To determine the maximum compressive strength and elastic modulus of samples, the reduced and non-reduced aerogels were compressed to 90% with a speed of 5 mm/min. Elastic modulus was calculated from the slope of the elastic region of the stress-strain curves. Cyclic compression tests were performed at 20, 40, 60, and 70% compressive strains through loading and unloading at a speed of 5 mm/min. Confocal microscope imaging was conducted using the Leica DMi8 confocal microscope. The emulsion gels were stained with Calcofluor White Stain and visualized using the confocal microscope. 7.4. Conductivity and electromagnetic shielding assessment The electrical conductivity and shielding measurements were carried out according to the procedures outlined in Chapter 5. 7.5. Rheology assessment: To evaluate the rheological characteristics of the prepared hydrogels, emulsion gels, and ionically crosslinked emulsion gels, a rotational rheometer (MCR 102 Anton-Paar rheometer) equipped with a parallel plate fixture (diameter: 25 mm, gap: 0.8 mm) was employed. The linear viscoelastic region (LVR) of prepared gels was first assessed by strain sweep (0.01–100%) at the frequency of 1 Hz. Frequency sweep tests were conducted from 0.0628–628 Hz at the strain of 0.1% (within LVR). Flow behavior test was performed at the shear rate range of 0.001–1000 s−1 to assess the nonlinear behavior of prepared samples. To evaluate creep and creep recovery, the developed gels 169 were subjected to the constant stress of 1 Pa for 100 s, followed by removing the load for 300 s. The elastic recovery test was performed by dynamic oscillatory strain cycles at 1 Hz through ten consecutive cycles of low-high strains, where in each cycle, a very low shear strain of 1% was applied for 5 min, followed by a high shear strain of 300% over the next 5 min. All tests were conducted at room temperature. 7.6. Results and discussion Figure 7.1 (a-b) illustrates the proposed method for fabricating jammed emulsion gels with precise nanoparticle compositions and concentrations. In this approach, the emulsion comprises two phases: aqueous and oil. The aqueous phase consists of two phases mixed in an equal (1:1 wt%) weight ratio. The phases of the aqueous medium involve a GO phase with a fixed concentration at 1 wt% and a CNC phase with a varying concentration from 1 to 3, 5, and 10 wt%. Meanwhile, the oil phase comprises hexane with 1 mg mL-1 of aminopropyllsobutyl polyhedral oligomerized silsesquioxane (POSS-NH2). Combining the water and oil phases in a 2:1 weight ratio (Figure 7.1 (a)), followed by thorough mixing at room temperature, yields a stable jammed emulsion gel (Figure 7.1 (b)). The formation of this gel is facilitated by electrostatic interactions between the positively charged protonated POSS-NH3+ and the deprotonated -COO- (carboxylic acid functional groups) of GO in synergy with the negatively charged CNC at the interfaces of the oil droplets and aqueous phase. The negative charge of the CNC stems from its hydroxyl (-OH) and sulfate half-ester groups (R-O-SO3-), which facilitate the interaction with assemblies and ligands at the interface 366. This interaction generates nanoparticle surfactants through interfacial complexation, which then jams at the interface (Figure 7.1 (c-d)), leading to a transition from liquid-like to solid-like behavior. Consequently, nanoparticle surfactant assemblies form at the water/oil interface, diminishing interfacial tension and stabilizing the emulsion. The formation of the emulsion gel 170 was confirmed through confocal microscopy, wherein the aqueous phase was stained with calcofluor white stain (Figure 7.1 (e-g)), elucidating the stable distribution and locking of oil droplets within the aqueous phase through interfacial complexation. The robust interfacial complexation between the ligand and nanoparticles at the interface of oil droplets and the aqueous phase was confirmed through interfacial tension (IFT) analysis using the KRÜSS DSA25 type pendant drop tensiometer (Figure 7.1 (h-j)). The IFT measurement revealed that the interface between water droplets and neat hexane initially was about 45.41 mN/m and remained consistent at around 42.84 mN/m when a droplet with a 1:1 weight ratio of 1 wt% GO and 1 wt% CNC suspensions (GO1 CNC1) was introduced, indicating the absence of interfacial complexation. However, upon the addition of POSS-NH2 to the oil phase, the IFT of GO1 CNC1 declined to 11.31 mN/m, showing the electrostatic interactions between nanoparticles and ligands. This leads to the jamming of the formed assemblies at the interface and stabilizes the emulsion. Of note, the IFT of the sole GO and CNC suspensions with the concentration of 1 wt% in the presence of POSS-NH2 in hexane was measured to be 3.56 and 26.77 mN/m, respectively. This indicates the higher interfacial activity of GO than CNC, showcasing the capability of GO to improve the integrity of the liquid construct upon its introduction along with the CNC to the system. The jamming of the nanoparticles was visualized via the contraction of the pendent droplet (Figure 7.1 (k)) through the wrinkle formation. This indicates the generation of solid elastic interfacial skin made of nanoparticle surfactants as a result of disordered overlapping assemblies of GO/CNC and POSS-NH2 at the interface, facilitating the formation of stable emulsion gel toward aerogel production. 171 Figure 7.1. (a) (I) Separated oil phase containing ligand (POSS-NH2) and an aqueous phase containing nanomaterials (GO and CNC) at desired concentrations before emulsification, and (II) the actual separated aqueous and oil phases containing nanoparticles and ligands, respectively; (b) (I) mixing and subsequent emulsification upon interfacial complexation, and (II) formation of emulsion gel. The scale bars in (a) (II) and (b) (II) are equal to 7.98 mm and 8.16 mm, respectively. These images were taken by a digital camera, and their scale bars are approximate. (c and d) A view of the jamming at the interface of the aqueous phase and oil droplets upon electrostatic interaction between the nanoparticles and ligands; herein, the blue rods show CNC, purple flakes show GO, and arrow-shaped objects in the droplets represent ligand (POSS-NH2). Confocal microscopy images of (e-g) GO1 CNC10 emulsion gel, in which the aqueous phase was stained with the calcofluor white stain; accordingly, the red phase showcases the presence of GO and CNC, while the black circles show the oil droplets containing ligands; the scale bars are equal to (e) 100 µm, and (f and g) 25 µm. Dynamic interfacial tension of (h) the neat water in hexane and GO1 CNC1 in hexane without any POSS-NH2, plus (i) GO1, CNC1, and GO1 CNC1 against hexane containing 1 mg mL-1 POSS-NH2. (j) Average interfacial tension before and after the addition of the ligand to the oil phase with or without the presence of various compositions of nanoparticles. (k) The contraction of the pendant drop and wrinkles formation, showcasing the jamming of the nanoparticles at the interface and formation of a solid skin as a result of overlapping assemblies of nanoparticles and ligands at the interface. 172 Rheology is a powerful tool for evaluating the stability and interfacial interactions between nanoparticles and reinforced droplets with the ligands. Using rheological characterization, the effect of CNC concentration on the rheological behavior of hydrogels and emulsion gels was thoroughly studied (Figure 7.2). Herein, the term “hydrogel” refers to the aqueous suspension of GO, CNC, or a combination of both, whereas the term “emulsion gel” is attributed to the jammed assembly of GO and CNC with POSS-NH2 at the oil/water interface. Figure 7.2 (a & b) shows the flow curves of hydrogels and emulsion gels, revealing their shear-thinning character owing to the disruption of the entangled network exposed to shear and probably the alignment and orientation of CNC rods along the shear direction 367. As evident, an increase in the CNC concentration from 1 to 10 wt% substantially enhanced the viscosity of hydrogels and emulsion gels, which is a crucial factor in 3D printing. In this case, at the shear rate of 0.1 (1/s), emulsion gels containing 1 and 10 wt% CNC showcased shear viscosities of 6×104 mPa.s-1 and 3×105 mPa.s-1, respectively. This indicates the increased likelihood of contact interactions among rod-like nanoparticles at higher concentrations of CNCs. More interestingly, as a result of interfacial complexation and jamming of the nanoparticles at the water/oil interface, the emulsion gels showcased higher viscosity than hydrogels, which is in accord with previous studies 31. The viscoelastic properties of emulsion gels provide a great in-depth insight into the real-time condition and interfacial interactions between the oil droplets and the nanoparticles, viz., GO and CNC. Accordingly, the obtained results from the strain sweep tests determined the linear viscoelastic region for hydrogels (Figure 7.3 (a)) and emulsion gels (Figure 7.4 (a)). Moreover, the storage (Gʹ) and loss (G") moduli versus angular frequency (frequency sweep data) were also analyzed for hydrogels and emulsion gels (Figure 7.2 (c & d)). According to these results, both hydrogel and emulsion gel systems revealed the dominance of gel-like behavior in which Gʹ and 173 Gʺ are relatively independent of frequency. However, in the hydrogel with 10 wt% CNC loading, a slight dependency on the frequency was observed. Moreover, both hydrogels and emulsion gels experienced higher values of Gʹ than Gʺ throughout the frequency range 368. The outcomes also showed the prevalence of elastic behavior in both hydrogels and emulsion gels, arising from a synergy between GO nanosheets and CNC macromolecules. Similarly, the increment of CNC concentration led to an increase in both moduli, leading to a more robust gel-like network 369. In comparison to their hybrid hydrogel counterparts containing GO and CNC, all emulsion gels exhibited higher dynamic moduli and a more pronounced difference between G' and G''. The discrepancy between G' and G'' was almost an order of magnitude in emulsion gels, in contrast to hydrogels, where the difference was less than an order of magnitude. This marked enhancement in shear viscosity and dynamic moduli indicates that the viscoelastic characteristics of emulsion gels are defined by their unique structure. This includes factors such as particle packing, assembly, nanoparticle jamming, droplet distribution, as well as interfacial stability and stiffness 31. Besides, the more robust elasticity of emulsion gels than hydrogels was underscored by the loss factor data (Figure 7.3 (b) and Figure 7.4 (b)), where the loss factor of both hydrogels and emulsion gels was below one across all angular frequencies. Nevertheless, the emulsion gels experienced lower values compared to the hydrogel counterparts. This outcome showcased a more pronounced elastic response in emulsion gels than in hydrogels. In alignment with previous analyses, the strain amplitude oscillatory shear tests also demonstrate significantly higher moduli and strain amplitudes at the yield point (where G' equals G'') for emulsion gels compared to their hydrogel counterparts (Figure 7.3 (a) and Figure 7.4 (a)). According to the results, the yield point for the hydrogel sample containing 1 wt% GO and 5 wt% CNC (GO1 CNC5) reached a strain amplitude of 18% and a modulus of 88.3 Pa, whereas the 174 corresponding values for the emulsion gel stood at 57% and 271 Pa, respectively. This outcome is advantageous, indicating that the solid-to-liquid viscoelastic transition in emulsion gel systems occurs at higher moduli and amplitudes compared to hydrogels, reflecting the more robust internal structure of the jammed emulsion systems. Furthermore, it is noteworthy that both hydrogels and emulsion gels exhibit similar shear-thinning behavior, as evidenced by the graphs plotting complex viscosity against frequency sweep (Figure 7.3 (c) and Figure 7.4 (c)). The creep-recovery assessments (Figure 7.2 (e & f)) were also performed to reveal the superiority of jammed emulsion systems over their hydrogel counterparts, including their stability and dynamic rheological properties. According to the creep compliance results (Figure 7.3 (d) and Figure 7.4 (d)), upon jamming of the nanoparticles at the interface and formation of the emulsion gel, a significant reduction in maximum compliance (Jmax), i.e., at t=100 s or when the applied load is taken off, occurred, indicating a decrease in emulsion deformation and an enhancement of elasticity. In this case, for the sample holding 1 wt% GO and 10 wt% CNC (GO1 CNC10), the Jmax value was changed from 0.06 Pa-1 for the hydrogel to 0.018 Pa-1 for emulsion gels. The reason for this difference is that when hydrogels are exposed to external forces, their network and molecular structures start to unravel once they pass their strain capacity. Meanwhile, in the jammed emulsion system, the formed robust interfacially driven assemblies at the interface significantly improved elasticity and resistance to deformation, surpassing those of hydrogel counterparts. However, the elastic recovery (Figure 7.3 (e) and Figure 7.4 (e)) assessment revealed the inability of the current form of jammed emulsion systems to hold their shape fidelity for the precision of 3D printing, as reversible structural breakdown and rapid recovery are crucial. The pertinent explanations are offered in the 3D printing section. Thereby, to address this challenge, sodium bicarbonate 175 (NaHCO3) was utilized as a salt to improve the viscoelastic properties of the emulsion gel, aiming to fulfill the requirements for DIW 3D printing, as discussed in the future sections. Figure 7.2. Rheological assessment of hydrogels and emulsion gels, including shear viscosity versus shear rate (flow curve) of (a) hydrogel and (b) emulsion gel; Gʹ and G" as a function of angular frequency (frequency sweep test) of (c) hydrogel and (d) emulsion gel; creep recovery test of (e) hydrogel and (f) emulsion gel. Figure 7.3. (a) The graphs of storage and loss moduli as a function of shear strain (the results of the frequency sweep data), (b) loss factor, and (c) complex viscosity versus angular frequency, (d) creep compliance as a function of time and (e) Gʹ and G" versus time (amplitude sweep tests or elastic recovery) of hydrogels. 176 Figure 7.4. (a) The graphs of storage and loss moduli as a function of shear strain (the results of the frequency sweep data), (b) loss factor, and (c) complex viscosity versus angular frequency, (d) creep compliance as a function of time and (e) Gʹ and G" versus time (amplitude sweep tests or elastic recovery) of emulsion gels. The jammed emulsion system's engineerable properties offer extensive versatility, enabling the creation of free-standing aerogels with customizable multi-scale porosities and adjustable density. To achieve this, the molded jammed emulsion gels are first frozen at -85°C using an ultra-low temperature freezer (Figure 7.5 (a) part I), followed by lyophilization (Figure 7.5 (a) part II), resulting in well-structured free-standing aerogel building blocks. These aerogels exhibit a porous core encased in a thin interfacial skin formed from nanoparticle surfactants, viz., interfacial complexation of GO and CNC at the interface. The core's porosity comprises two distinct types: larger pores derived from the stabilized oil droplets via the ligand, and smaller pores originating from the stacked GO flakes synergizing with CNCs. This dual-scale porosity structure is evident in FESEM images (Figure 7.5 (b and c)), showcasing a combination of large and small pores within the aerogel core, surrounded by an interfacial skin. The outcome of this process led to ultralight-weight free-standing aerogels that the light hairs of a cactus can withstand their weight (Figure 7.5 (d)). Moreover, the ability to control the process enables precise adjustments of aerogel density 177 across a broad spectrum by variating the nanomaterial concentration during emulsification. For non-reduced aerogels, density can vary from 6.25 to 31.13 mg/cm³, while for reduced aerogels, the range is from 2.63 to 11.70 mg/cm³ (Figure 7.5 (e)). This control is further exemplified following thermal annealing (800 °C under Ar for 1 h), where we observe volume shrinkage falling between 14.88% and 27.94% as CNC loading increases (Figure 7.5 (f)). This level of control holds significant promise for advanced applications such as EMI shielding, where precise management of porosity, density, and generation of conductive networks is crucial. Figure 7.5. Formation of free-standing aerogel building blocks through (a) (I) freezing of the molded jammed emulsion gels and (II) their subsequent lyophilization yields a multi-scale porous aerogel with large pores made of stabilized oil droplets and smaller pores originating from the well-stacked GO flakes integrated with CNCs. FESEM images of free-standing aerogels made of (b) GO1 CNC1, and (c) GO1 CNC10; scale bars are equal to (b) 500 µm, and (c) 200 µm. 178 (d) Free-standing non-reduced GO1 CNC1 aerogels standing on the light hairs of a cactus; the scale bar is equal to 7.87 mm; of note, this image was taken by a digital camera, and the scale bar is approximate. (e) Density variation of the aerogels upon increase in the CNC loading and their thermal annealing. (f) Volume shrinkage of aerogels after thermal annealing at different CNC loadings. The successful synergy between the GO/CNC and POSS-NH2 through interfacial complexation and the generation of the conductive carbonaceous pathway was thoroughly supported by the outcome of the X-ray diffractogram, micro-Raman spectroscopy, and FTIR. The as-developed free-standing aerogels were examined via X-ray diffraction using a polycapillary collimating optic to assess their crystalline structure and proper synergistic co-assembly of the CNC and GO within the hierarchical framework of aerogels. The employed method diminishes the errors associated with the instrumental errors and sample displacement that could cause asymmetric peak broadening when examining samples with rough or non-even surfaces such as porous structures or aerogels. Figure 7.6 shows the X-ray diffraction of non-reduced aerogels using polycapillary optics with an increasing CNC concentration. As demonstrated, the assembled GO flakes in the aerogels framework illuminated their peak related to the (001) crystalline plane of GO at 2Ѳ positions of 10.23, 10.26, 10.26, and 10.09° corresponding to d-spacings of 8.64, 8.61, 8.61, and 8.76 Å, respectively (Table 7.2). This soar in the d-spacing compared with the neat graphite (3.4 Å) shows the existence of hydrophilic oxygen-based functional groups, affecting the spacing between the GO flakes 25. Of note, upon an increase in the concertation of CNC from 1 wt% to 10 wt% (Figure 7.6 (a-d)), the intensity of the corresponding 2Ѳ peak of GO declined, and the fingerprint peaks of CNC were more profoundly observed. As depicted, 2Ѳ characteristic peaks of (1-10), (110), (102), (200), and (004) crystalline planes of CNC were observed in the XRD patterns, confirming the co-assembly of the GO and CNC in the jammed emulsion gel-based aerogels 370, 371; Table 7.2 shows the full list of corresponding 2Ѳ peaks and their corresponding d-spacing. 179 Figure 7.6. The X-ray diffraction of non-reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels. Table 7.2. Extracted information from the X-ray diffractions of non-reduced aerogels. Sample 2Ѳ Peak (°) Crystalline Plane d-spacing (Å) Source GO1 CNC1 10.23 (001) 8.64 GO 14.92 (1-10) 5.93 CNC 16.17 (110) 5.48 CNC 22.47 (200) 3.95 CNC 34.43 (004) 2.60 CNC GO1 CNC3 10.26 (001) 8.61 GO 14.96 (1-10) 5.91 CNC 16.31 (110) 5.42 CNC 22.56 (200) 3.93 CNC 34.44 (004) 2.60 CNC GO1 CNC5 10.26 (001) 8.61 GO 14.85 (1-10) 5.96 CNC 16.55 (110) 5.35 CNC 20.19 (102) 4.39 CNC 22.46 (200) 3.95 CNC 34.55 (004) 2.59 CNC GO1 CNC10 10.09 (001) 8.76 GO 14.95 (1-10) 5.92 CNC 16.67 (110) 5.31 CNC 20.19 (102) 4.39 CNC 22.47 (200) 3.95 CNC 34.58 (004) 2.59 CNC 180 Upon reduction of aerogel with 1 wt% GO and 1 wt% CNC (GO1 CNC1) at 800 °C under Ar for 1 h, the whole X-ray diffraction pattern changed to a single broad peak at 2Ѳ of 25.81 equal to the d-spacing of 3.4 Å, corresponding to the graphite d-spacing (Figure 7.7 (a)). Upon further increase in the content of carbonized CNC (1-10 wt%) while keeping the GO at 1 wt%, the corresponding 2Ѳ peak shifted to lower degrees of 25.2, 24.7, and 24.7 for GO1 CNC3, GO1 CNC5, and GO CNC10, attributed to the d-spacing of 3.5, 3.6, and 3.6 Å, respectively (Figure 7.7 (b-d) and Table 7.3). The obtained results clearly showcased the removal of oxygen domains and the formation of reduced GO flakes coupled with carbonized CNCs, forming a carbonaceous framework with restored electrical conductivity 109. Figure 7.7. The X-ray diffraction of reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels. 181 Table 7.3. Extracted information from the X-ray diffractions of reduced aerogels (800 °C under Ar for 1 h). Sample 2Ѳ Peak (°) d-spacing (Å) GO1 CNC1 25.81 3.44 GO1 CNC3 25.26 3.52 GO1 CNC5 24.70 3.60 GO1 CNC10 24.77 3.59 In accord with previous analyses, micro-Raman spectroscopy results revealed two well-known characteristic peaks of GO at about 1324-1351 cm-1 and 1574-1588 cm-1 in all non-reduced and reduced aerogels, attributed to the D-band and G-band of GO flakes (Figure 7.8) 109. ID/IG ratio of the non-reduced GO1 CNC1 aerogel as a representee of the disorder in the flakes was measured to be 0.83 and soared to 0.95 upon further increase in the content of CNC to 10 wt% (Table 7.4). Moreover, the thermal annealing of aerogel samples increased the value of the ID/IG ratio, showing the increase in defective sites upon the removal of oxygen-based functional groups and the remnant of vacancies on assembled reduced flakes and carbonized CNCs within the aerogel’s framework (Table 7.4). 182 Figure 7.8. Micro Raman spectroscopy of non-reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels, and reduced (e) GO1 CNC1, (f) GO1 CNC3, (g) GO1 CNC5, and (h) GO1 CNC10 aerogels. 183 Table 7.4. Extracted data from the micro-Raman spectroscopy of lyophilized aerogels before and after thermal annealing. Sample D-band G-band ID/IG Non-reduced GO1 CNC1 1351 cm-1 1588 cm-1 0.83 Non-reduced GO1 CNC3 1344 cm-1 1582 cm-1 0.90 Non-reduced GO1 CNC5 1338 cm-1 1586 cm-1 0.90 Non-reduced GO1 CNC10 1324 cm-1 1576 cm-1 0.95 Reduced GO1 CNC1 1339 cm-1 1581 cm-1 1.06 Reduced GO1 CNC3 1341 cm-1 1587 cm-1 1.08 Reduced GO1 CNC5 1346 cm-1 1577 cm-1 0.98 Reduced GO1 CNC10 1347 cm-1 1574 cm-1 0.97 Furthermore, the FTIR spectrums of non-reduced and reduced aerogels of GO and CNC were provided in Figure 7.9. As depicted in parts (a) to (d), non-reduced aerogels showcased FTIR spectrums with nearly the same peak positions but with elevated intensities upon an increase in the concentration of CNC from 1 to 10 wt%. The obtained spectrums demonstrated the fingerprint peaks of GO, CNC, and POSS, revealing the synergistic co-assembly of the GO and CNC in interaction with POSS during the nanoparticle surfactant formation and subsequent generation of aerogels after freezing and lyophilization. The POSS molecule showed its corresponding peaks to the stretching vibration of Si-C (836-838 cm-1), stretching vibration of Si-O-Si siloxane groups arising from the absorption of silsesquioxane cages (1106-1108 cm-1), Si-C (1224-1253 cm-1), and stretching vibration of C-H groups related to the six pendant organic arms of the POSS molecules, indicating the placement of the POSS in the structure 139, 142, 143. At the same time, GO also showed two of its main FTIR fingerprints at about 1635-1648 cm-1 and 1733-1739 cm-1, attributed to the C=C and C=O stretching vibrations 109. Cellulose nanocrystals showed their signature by revealing corresponding peaks to 𝛽-glycosidic linkage (896-898 cm-1), pyranose ring’s -C-O bond (1056-1058 cm-1), wagging deformation mode of CH2 at C6 (1317-1319 cm-1), and -CH2 scissoring within the cellulose structure (1427-1428 cm-1) 370, 372, 373. The merged hydroxy (-OH) functional groups of jammed nanoparticles during the interfacial assembly and subsequent aerogel formation 184 showed a broad peak at about 3342-3345 cm-1 109. Upon thermal annealing of the aerogels (Figure 7.9 (e-h)), the corresponding peaks to the functional groups were diminished or vanished, showing the successful reduction of aerogels and formation of a carbonaceous framework with restored electrical conductivity. Figure 7.9. FTIR spectroscopy of non-reduced (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 aerogels, and reduced (e) GO1 CNC1, (f) GO1 CNC3, (g) GO1 CNC5, and (h) GO1 CNC10 aerogels. 185 The formed nanoparticle surfactant derivated thin skin around the non-reduced free-standing aerogels GO1 CNC1 (Figure 7.10) and GO1 CNC10 (Figure 7.11). Upon lyophilization of the formed emulsion gels made of jamming of GO-CNC and POSS at the interface, free-standing aerogels were formed with a porous core sounded by a thin layer of jammed assemblies. Figure 7.10. FESEM images of the (a) bulk free-standing non-reduced GO1 CNC1 aerogel and its (b-f) skin made of nanoparticle surfactants. Scale bars are equal to (a) 2 mm, (b) 500 µm, (c) 10 µm, (d-f) 5 µm. 186 Figure 7.11. FESEM images of the (a) bulk free-standing non-reduced GO1 CNC10 aerogel and (b-f) the skin surrounding the aerogel made of nanoparticle surfactants. Scale bars are equal to (a) 2 mm, (b) 1 mm, (c) 500 µm, (d) 200 µm, (e) 100 µm, and (f) 20 µm. Crucially, the naturally weak mechanical properties and structural integrity of aerogels have driven the need to create a robust, hierarchically organized porous medium. The innovative structure presented in the current study allows for adjusting mechanical attributes, ranging from flexible to highly stiff ones, with significant ultimate strength, as required by specific applications. We embarked on this journey to enhance aerogel mechanical performance by drawing on the engineerable properties of jammed emulsion gel. In our pursuit, the emulsification process provided a pathway for achieving our goal. By elevating the concentration of CNCs during emulsification, we effectively fine-tuned the mechanical robustness of the resulting aerogels, significantly enhancing their ultimate strength (Figure 7.12 (a and b)). Notably, the GO1 CNC10 aerogel demonstrated remarkable mechanical robustness, easily withstanding a half-kilogram load 187 without any sign of plastic deformation (Figure 7.12 (c)). Examining stress-strain curves depicted in Figure 7.12 (a and b), we observed three distinct regions characterizing cellular aerogels. Initially, a linear elastic region emerged with relatively minor strain (less than 15%). This phase evolved into a pseudo-plateau region characterized by a strain range of 15% to 70%. It was subsequently followed by a distinct compaction phase, marked by a notable surge in stress at higher strains, specifically beyond the 70% threshold. Remarkably, augmenting CNC concentration from 1 to 10 wt% accentuated the initial rise, attributed to the reinforcing effect of CNCs at higher concentrations. Under higher compressive strains, the deformation of aerogels predominantly takes place through the densification of their porous framework. This process involves the walls of the macropores coming into contact, thus playing a critical role in bearing the applied load. Additionally, the presence of GO sheets played a pivotal role in averting aerogel deformation and improving the construct's integrity. This also prevents the collapse of the CNC network by keeping them in close proximity. Quantitative assessments revealed that aerogels prepared with 1, 3, 5, and 10 wt% CNC exhibited ultimate compressive stresses of 43.07, 108.08, 183.70, and 251.86 kPa, respectively, surpassing the ultimate compressive strength values for previously reported aerogels, including 1.2 kPa for cellulose nanofiber (CNF) aerogel 307, 12.1 kPa for carbon aerogels 374, and 3.7 kPa for CNC aerogels 375. Furthermore, rheological evaluations highlighted that increasing CNC loading significantly intensified interactions and the likelihood of short-range contact interactions due to densification and reduced CNC-to-CNC distances, akin to entanglement phenomena observed in cellulose nanofibers 376. Conversely, the compressive stress and corresponding modulus values decreased by nearly half following the carbonization process. For instance, the compressive stress and Young modulus of GO1 CNC10 aerogel were 251.86 kPa and 458.24 kPa, while the 188 corresponding values for the carbonized counterparts were 122.03 kPa and 92.12 kPa, respectively (Figure 7.12 (d)). This could be due to the removal of the oxygen-based moieties and CNCs’ carbonization, which leads to their rearrangement and decline in the cellular structure’s robustness, thereby declining the ultimate compressive strength until reaching structural failure. These findings underscore the efficacy of our approach in tailoring aerogel mechanical properties through simple concentration adjustments or post-processing techniques. Interestingly, while conventional CNC-based aerogels typically exhibit a rigid structure with limited flexibility, the aerogels produced in this study offer a remarkable ability to withstand compressive strains while swiftly recovering their original shape with minimal plastic deformation (Figure 7.12 (e and f)). To assess the shape recovery and fatigue resistance of the flexible CNC-based porous medium, reduced GO1 CNC1 aerogel was subjected to various strains (Figure 7.12 (e)). As depicted, the reduced CNC-based aerogel displayed excellent elasticity under diverse strain conditions, sustaining a significant compression strain of 70% without collapsing and promptly reverting to its initial form. Remarkably, at a strain of 70%, the corresponding compressive stress reached about ~6 kPa, showcasing the specific strength (ultimate compressive strength over density) of 2,281.36 kPa cm3 g-1. Such high specific strength shows the outstanding mechanical robustness of the aerogel, considering its ultra-low density. The exceptional elasticity of the prepared aerogel (reduced GO1 CNC1) was further validated through its enduring cyclic performance during 100 continuous loading-unloading compression cycles (Figure 7.12 (g)). Correspondingly, the modulus sharply declined from 4.3 kPa in the first cycle to 1.93 kPa by the 20th cycle, followed by a very slight decline to 1.51 kPa in the 100th cycle (Figure 7.12 (h)). This shows the proper cycled stability of these aerogels comparable to that of previously documented hemp aerogels and CNC-based carbon aerogels 377, 378, highlighting their 189 durability through successive compression loading-unloading cycles. The production of free-standing aerogels, facilitated by interfacial complexation between GO/CNC and POSS-NH2 demonstrates mechanical robustness that can be engineered. This robustness increases with CNC loading, leading to a more durable porous network than recently developed aerogels (Figure 7.12 (i) and Table 7.5). This advancement tackles a pivotal challenge by enabling the precise tuning of aerogel mechanical properties, thereby allowing for the engineering of aerogels to range from flexible and soft constructs to stiffer ones with high ultimate strength as needed. This innovation paves the way for novel designs and functionalities within the domain of lightweight materials. 190 Figure 7.12. Stress-strain curves of (a) non-reduced and (b) reduced aerogels at various CNC concentrations. (c) A non-reduced GO1 CNC10 aerogel capable of holding a half-kilogram weight without any plastic deformation; the scale bar is equal to 13.22 mm; this image is taken by a digital camera, and the scale bar is approximate. (d) The elastic modulus of the reduced and non-reduced aerogels at different CNC loadings. (e) Cyclic compression of reduced GO1 CNC1 aerogels with six repeated compression cycles at different strains (20 to 70%), and (f) elastic resilience of the as-developed aerogels capable of undergoing large strains (80%) and recovering their shape with the least plastic deformations; the image shows the aerogels in (i) initial state, (ii) compression, and (iii) shape recovery upon force release. (g) The compressive cyclic stability of the reduced GO1 CNC1 aerogel after 100 loading-unloading compression cycles at the strain of 40%. (h) Change in the elastic modulus of the reduced GO1 CNC1 aerogel after 100 loading-unloading compression cycles. (i) The ultimate compressive strength of the as-developed aerogels compared with recent practices in the field by considering their lightness; of note, the unit of the x-axis is in logarithmic order. 191 Table 7.5. The mechanical performance and density of the free-standing reduced/non-reduced aerogels holding different concentrations of CNC compared with the recent practices in the field. Aerogels Density (mg cm-3) Compression Strength (kPa) Compressive Strain (%) Ref. 3D-printed Ti3C2Tx aerogel 9.73-15.69 1-4 50 161 Ni-Ti3C2Tx-rGO aerogel 6.45 ~5.7 20 379 CNC aerogel 5.6 ~45 90 154 rGO-CNF (20 wt%) aerogel 3.46 4.63 50 380 CNF aerogel 6.04 5.76 70 381 Cellulose Aerogel-air dried 58.8 72 70 382 Cellulose Aerogel-freeze dried 57.9 90 70 382 CNT aerogel 11.88 ~115 80 153 Nanofibrous CNT/SiO2 aerogel 6.2 7 80 160 Silica aerogel 53.5 35 90 163 Silica aerogel 64-98 ~240 55 162 Graphene aerogel 3-5 19 90 149 Graphene aerogel 1-12 ~60 80 93 Graphene aerogel 2-10 ~9.5 50 157 Graphene aerogel 5-7.8 45 95 158 rGO aerogel 5-7.8 140 95 158 Filamentous graphene aerogel 3.12 4.1 90 109 3D-printed PVA/graphene aerogel 6.5 ~55 10 155 Graphene nanoribbon aerogel 9.33 ~100 80 153 Carbon aerogel 9.2 40 70 159 Carbon aerogel 5.2 ~11 80 156 Carbon aerogel 22.4 0.8 50 150 Non-reduced GO1 CNC1 Aerogel 6.25 43.07 - This Study Non-reduced GO1 CNC3 Aerogel 11.76 108.08 - Non-reduced GO1 CNC5 Aerogel 16.47 183.70 - Non-reduced GO1 CNC10 Aerogel 31.13 251.86 - Reduced GO1 CNC1 Aerogel 2.63 15.92 70 Reduced GO1 CNC3 Aerogel 4.44 31.29 - Reduced GO1 CNC5 Aerogel 6.11 44.58 - Reduced GO1 CNC10 Aerogel 11.70 122.03 - Abbreviations: Cellulose nanocrystal (CNC), cellulose nanofiber (CNF), carbon nanotube (CNT), reduced graphene oxide (rGO), and polyvinyl alcohol (PVA). The abundant multi-scale porosities combined with the outstanding mechanical robustness of emulsion-templated aerogels offer substantial benefits for different applications. However, meeting the requirements of advanced applications necessitates the adjustment of the macroscopic arrangement through additive manufacturing. This allows for the control of the 3D spatial arrangement through computer-guided DIW. However, DIW of interfacially jammed emulsion gels requires an optimal shear-thinning character with high printing resolution and structural integrity. Addressing this challenge requires fine-tuning the rheological and viscoelastic properties of the jammed emulsion gels to enable shape fidelity and fast recovery over the 3D printing process. The 192 jammed emulsion gels of GO and CNC failed to print smoothly, as they lacked proper viscoelastic features such as shape retention and recovery after deposition of extruded filaments on the 3D printer bed (Figure 7.13 (a)). This was evident in the elastic recovery test of the prepared emulsion gels (Figure 7.4 (e)), where the improper reversibility and recovery of the emulsion gels were evident. To address this challenge, we conducted a secondary post-jamming ionic crosslinking by incorporating NaHCO3 salt into the aqueous phase of GO1 CNC10 emulsion gel. Accordingly, a 3D-printable ink through DIW requires a strong shear-thinning character, allowing smooth flowability of the ink through the nozzle. To achieve a solid-like response and maintain the filamentary morphology of the extruded filament during 3D printing, it is essential to meet specific criteria, including a sufficiently high storage modulus (G′) and yield point (or yield stress (τy)). Incorporating the NaHCO3 addressed this requirement by enhancing the shear-thinning behavior of the emulsion gel, making it a 3D-printable jammed emulsion gel-based ink (Figure 7.13 (b-c)). For ease of follow-up, the GO1 CNC10 jammed emulsion gel with and without NaHCO3 complexation is denoted as EG-Salt and EG, respectively, to facilitate a better comparison upon salt addition to the emulsion system (Figure 7.13 (c-f)). The shear-thinning behavior of the GO1 CNC10 emulsion gel and its post-jamming ionically crosslinked counterparts (Figure 7.13 (c)) were compared via the power law index (n) or flow index according to the power-law model ( ( )1.nk −= ). This equation expresses the flow behavior of the prepared inks in which k, n, and  are constant called consistency index (known as the viscosity once the shear rate is 1 s−1), the flow index, and the shear rate, respectively 368. Accordingly, the calculated n index for the GO1 CNC10 emulsion gel and its post-jamming ionically crosslinked form with the NaHCO3 salt was calculated to be 0.180 and 0.021, respectively. This illuminates the enhanced shear-thinning character of the ionically crosslinked 193 emulsion gel compared with the non-crosslinked one, paving the way toward 3D printable emulsion inks. Such noteworthy enhancement stems from the intricate interplay of salt complexation with CNCs within the aqueous phase of the emulsion gel. CNC rods possess inherent negative charges due to their hydroxyl (-OH) and sulfate half-ester (R-O-SO3-) functional groups, which enhance their stability in aqueous environments. Upon salt integration, the electric double layer surrounding the CNCs undergoes compression, facilitated by the influx of counterions from the salt, thereby stabilizing the surface charges of the CNCs. This compression reduces repulsive forces among CNCs, minimizing the interparticle distance and thereby enhancing the viscoelastic properties of the CNC suspension 361, 366. In the case of NaHCO3 salt, its dissociation in water amplifies the propensity for hydrogen bonding within the system. This dissociation fosters hydrogen bonding interactions between H+ or O- and -OH (hydroxyl) groups, facilitating ion-dipole interactions between sodium ions (Na+) and water molecules, as well as dipole-dipole interactions between HCO3− and water. Consequently, this augmentation bolsters the viscoelastic properties of the emulsion gel, concurrently impeding the mobility of CNC clusters. Likewise, the incorporation of Na+ into the system results in CNC clusters through the screening surface charges, generating a more condensed network 361. As a result, the fine-tuned intermolecular interactions by the salt act as a secondary step to maintain the printing quality and shape retention of the jammed emulsion gel. The dynamic moduli versus strain for both EG-Salt and EG (Figure 7.13 (d)) revealed that ionically crosslinked emulsion gel exhibited predominantly elastic behavior at low shear strain values (where G' > G''), with the critical strain (the yield point where G'' = G') being around 10%. In contrast, for the EG (GO1 CNC10 emulsion gel), the yield point occurred at a lower strain of 1%. These observations highlight the beneficial effect of NaHCO3 salt on enhancing the rheological 194 properties, such as the yield point of the jammed emulsion gels, which has a significant impact on the 3D printing capability. The predominance of elastic behavior (G' > G'') in the prepared ink is evident from the dynamic moduli versus angular frequency plots (Figure 7.13 (e)). Additionally, the elastic recovery of the prepared emulsion gel-based inks was assessed through strain amplitude sweep tests conducted at various time intervals, applying both low (1%) and high (300%) shear strains (Figure 7.13 (f)). When the strain was increased to 300%, exceeding the critical strain, G' significantly decreased from approximately 3145 Pa to about 1.5 Pa, indicating the disruption and collapse of the ink's 3D network structure. Furthermore, at a high strain of 300%, where G' < G'', viscous behavior became dominant. On the other hand, when the strain was reduced to 1%, G' rapidly returned to its original value, demonstrating the exceptional recoverability of the prepared crosslinked emulsion gel-based ink. The ink's network disruption and its subsequent recovery proved to be reversible across ten consecutive oscillatory deformation and recovery cycles, affirming its strong elastic recovery capabilities essential for maintaining the shape retention of extruded filaments. Based on these results, introducing a secondary ionic crosslinking improved the viscoelastic properties of CNC-based emulsion gels and allowed governing the intermolecular interactions between CNC rods in the aqueous phase without disturbing the jammed assemblies. This dictates the desired shape retention and elastic recovery to the jammed assemblies toward the precision of 3D printing. The confocal microscope images of the ionically crosslinked emulsion gels (Figure 7.13 (g and h)) showcased a precisely organized jammed emulsion system. Interestingly, the incorporation of post-jamming ionic crosslinking did not disrupt the nanoparticle surfactant assemblies at the interface, presenting an exciting prospect for fine-tuning the viscoelastic properties of emulsion gels. This provides a great opportunity for fine-tuning the 195 viscoelastic character of jammed emulsion gels toward additive manufacturing and generating complex geometries on demand. Figure 7.13. (a) The inability of the GO1 CNC10 emulsion gel to retain its shape fidelity upon DIW, and (b) the 3D-printable post-jamming ionically crosslinked GO1 CNC10 emulsion gel, capable of maintaining its shape and printing resolution because of the improved viscoelastic properties and shear thinning behavior. The scale bars are equal to (a) 13.30 mm, and (b) 9.84 mm; these images were taken by a digital camera, and their scale bars are approximate. The rheological characterization of the ionically crosslinked GO1 CNC10 emulsion gel (EG-Salt) and GO1 CNC10 emulsion gel (EG), including (c) shear viscosity a function of the shear rate, (d) Gʹ and G" against strain, (e) Gʹ and G" versus angular frequency, and (f) elastic recovery test. (g & h) Confocal microscopy images of the ionically crosslinked GO1 CNC10 jammed emulsion gel, showcasing the stability of the oil droplets in the aqueous phase and the stability of the emulsion system even upon a secondary ionic crosslinking by NaHCO3 salt. 196 Such control over the viscoelastic characteristics of the emulsion gel and improving its shear-thinning behavior allow for controlling the macroscopic morphology of the aerogel through computer-guided 3D printing using DIW. Using a bio 3D printing setup, the DIW of post-jamming ionically crosslinked jammed emulsion gels enables the tuning of morphology and 3D spatial arrangements. This process results in the creation of 3D-printed aerogels through subsequent freezing and lyophilization steps (Figure 7.14 (a)). These steps yield ultra-lightweight, 3D-printed porous constructs, as shown in Figure 7.14 (b). This approach enables controlling and boosting the porosity of the aerogels from macro- down to micro-scale, which is beneficial for porosity-wise applications such as EMI shielding (Figure 7.14 (c-e)). Likewise, the programmable nature of additive manufacturing provides the possibility of making complex geometries on demand (Figure 7.14 (f & g)), which is crucial for advanced applications and designs. The FESEM analysis of the frozen and then lyophilized 3D-printed inks revealed a nearly uniform and consistent filament diameter. In this regard, filaments printed using a gauge 30 nozzle, which has an inner diameter (ID) of 159 µm, exhibited an average diameter of 315.89±13.30 µm based on 100 measurements, as depicted in Figures 7.15 and 7.16. This uniformity in filament diameter enables the 3D printing of complex geometries that maintain consistent filament morphology and micro-scale porosities, illustrated in Figures 7.17 to 7.23. Furthermore, thermal annealing of the 3D-printed aerogel (800 °C for 1 h under Ar) allows the generation of a conductive network as well as the shear alignment of the graphene flakes in the direction of the 3D-printing (Figure 7.14 (h-l)). Accordingly, upon extruding the ink containing GO and CNC, the shear force aligns them in the direction of printing, generating an aligned reduced carbonaceous network. This was evident in further FESEM and EDX analyses, as demonstrated in the supporting information (Figure 7.24-7.27). 197 Figure 7.14. (a) From 3D printing of the ionically crosslinked jammed emulsion gel to freezing and lyophilization for making aerogels with controllable spatial arrangement. (b) Ultra-lightweight 3D printed GO1 CNC10 aerogels with complex geometries standing on the light hairs of a cactus. FESEM images of the 3D printed aerogel grids from (c) macro-scale up to (d-e) micro-scale porosities. (f-g) FESEM images of 3D printed aerogels with complex geometries. (h) FESEM image of the reduced 3D printed GO1 CNC10 aerogel, and (i-j) EDX mapping of the reduced 3D printed GO1 CNC10 aerogel showing the dominant carbon content and the restoration of the conductive carbonaceous network; (k and l) FESEM images of the micro-scale porosities of the reduced 3D printed GO1 CNC10 aerogel, showcasing their shear-induced alignment. Scale bars are equal to (b) 10.02 mm, (c) 500 µm, (d) 50 µm, (e) 1 mm, (f) 1 mm, (g) 2 mm, (h) 1 mm, (i) 1 mm, (j) 1 mm, (k) 500 µm, and (l) 50 µm. The image in part (b) was captured with a digital camera, and the scale bar is approximate. 198 Figure 7.15. FESEM images from the 3D-printed filaments of ionically crosslinked GO1 CNC10, showing the uniform filament diameter. The scale bars are equal to (a) 1 mm and (b-c) 500 µm. Figure 7.16. The average filament diameter of 3D-printed aerogels, printed by a needle with gauge number 30 (I.D. of 0.159 mm). 199 Figure 7.17. FESEM image of the 3D-printed ionically crosslinked GO1 CNC10 aerogel grids with 3 mm in-fill distance showing (a-c) macro-scale porosities and (d) micro-scale porosities. Scale bars are equal to (a-c) 1 mm and (d) 500 µm. 200 Figure 7.18. (a) FESEM image of the 3D-printed post-jamming ionically crosslinked GO1 CNC10 aerogel grids and (b-c) its EDX mapping. Figure 7.19. EDX analysis of 3D-printed ionically crosslinked GO1 CNC10 aerogel. 201 Figure 7.20. (a) FESEM image of the micro-scale porosity of 3D-printed ionically crosslinked GO1 CNC10 aerogel, and (b-c) its EDX mapping. Figure 7.21. EDX analysis of the micro-scale porosity of 3D-printed ionically crosslinked GO1 CNC10 aerogel. 202 Figure 7.22. (a) FESEM image of the triangular-shaped 3D-printed ionically crosslinked GO1 CNC10 aerogel and (b-c) its EDX mapping. 203 Figure 7.23. (a) FESEM image of the micro-scale porosity of triangular-shaped 3D-printed ionically crosslinked GO1 CNC10 aerogel, and (b-c) its EDX mapping. 204 Figure 7.24. FESEM images of thermally annealed (800 °C, under Ar for 1 h) 3D-printed GO1 CNC10 aerogels showcasing (a-c) macro-scale porosity and (d-k) micro-scale porosities. As demonstrated, applying the shear force to the emulsion ink led to the alignment of the GO flakes in the direction of printing. Scale bars are equal to (a) 2 mm, (b) 1 mm, (c) 500 µm, (d) 500 µm, (e) 500 µm, (f) 200 µm, (g) 100 µm, (h) 20 µm, (i) 10 µm, (j) 10 µm, and (k) 10 µm. 205 Figure 7.25. (a) FESEM image of thermally annealed 3D-printed chemically crosslinked GO1 CNC10 aerogel grids and (b-c) its EDX mapping. Figure 7.26. EDX analysis of thermally annealed 3D-printed chemically crosslinked GO1 CNC10 aerogel. 206 Figure 7.27. (a) FESEM image of the micro-scale porosity of thermally annealed 3D-printed ionically crosslinked GO1 CNC10 aerogel and (b-c) its EDX mapping. 207 Aerogels derived from emulsion gels pave the way for the development of innovative porous shielding structures, notable for their outstanding total shielding effectiveness at low densities. Further carbonizing these 3D-structured aerogels generated a conductive porous carbonaceous framework, enhancing their ability to attenuate incident electromagnetic waves. Accordingly, thermal annealing of free-standing aerogels with an enhanced CNC content from 1 to 5 wt% showcased an ascending trend for electrical conductivity starting from 6.5 S/m for GO1 CNC1 to 14.6 and 16.3 S/m for GO1 CNC3 and GO1 CNC5, respectively. However, a further increase in the CNC content to 10 wt% (GO1 CNC10) led to a slight decline in the electrical conductivity to 13.4 S/m (Figure 7.28 (a)). The thermally annealed aerogels, characterized by their finite electrical conductivity and porous structure, emerge as effective shielding systems. When analyzed, the free-standing aerogels, with a thickness of 10 mm, displayed total shielding effectiveness (SET) within the range of 51.59 dB to 79.46 dB (Figure 7.28 (b) and Figure 7.29). This level of effectiveness was consistently observed across carbonized aerogels containing 1, 3, 5, and 10 wt% CNC. Moreover, the GO1 CNC1 and GO1 CNC3 variants of carbonized free-standing GO aerogels demonstrated an absorption-dominant shielding behavior, with absorbance (A) and reflection loss (SER) values ranging between 0.52-0.54 and 2.78-2.65 dB, respectively, as shown in Figures 7.28 (b) and (c). However, increasing the CNC content to 5 and 10 wt%, i.e., in GO1 CNC5 and GO1 CNC10, altered the shielding mechanism to become reflection-dominant, with A and SER values adjusting to 0.42-0.47 and 3.24-3.79 dB. Furthermore, all variations of the free-standing aerogels demonstrated nearly consistent shielding effectiveness throughout the entire X-band frequency range of 8.2-12.4 GHz, as depicted in Figure 7.28 (d). Additionally, the specific shielding effectiveness per unit thickness (SSE/t) values for the 208 aerogels, with reduced graphene oxide and varying CNC contents of 1, 3, 5, and 10 wt%, were recorded at 19615.96, 17626.12, 12891.98, and 6791.45 dB cm² g⁻¹, respectively. These findings highlight the aerogels as highly efficient, ultra-lightweight shielding systems, where their effectiveness is primarily attributed to the interfacial complexation within their structure and the formation of a lightweight multi-scale porous construct. Interestingly, the shear alignment of the porous conductive carbonaceous network of the 3D-printed GO1 CNC10 aerogel during DIW led to an increase in the electrical conductivity of the aerogels to 19.63 S/m after thermal annealing. This significantly enhanced the shielding effectiveness of the 3D-printed aerogels at lower thicknesses. In this case, the 3D-printed aerogels with 1-4 mm thickness showed reflection-dominant shielding character (A and SER ranging between 0.31-0.27 and 3.7-5.6 dB, respectively) with SET of 16.7-38.2 dB and nearly stable SET over the whole X-band frequency range (Figures 7.28 (e and f) and Figure 7.30). The promoted reflection-dominant shielding behavior of the 3D-printed aerogels is due to the enhanced electrical conductivity of the aerogels as a result of shear-induced alignment during DIW, which facilitates impedance mismatching and increases the rate of scattered EM waves in the form of reflection from the shield’s surface. The remarkable shielding properties of thermally annealed aerogels stem largely from their rich multi-scale porosity embedded within a conductive network. This structure enhances multiple scatterings within the pores and significantly dissipates the energy of EM waves as heat, especially when paired with conduction loss. This combination efficiently mitigates EM wave energy, leveraging both the material's intricate porosity and its conductive properties for superior shielding performance 25, 110 (Figure 7.28 (g)). This makes the proposed method a promising approach for porosity-wise applications such as EMI shielding, as by altering the porosity level, nanomaterial composition/arrangement, and aerogel morphology, the shielding character can be controlled 109. 209 However, an increase in the electrical conductivity of 3D-printed aerogels, triggered by shear-induced alignment during printing, led to increased surface reflection and impedance mismatching, significantly exceeding those observed in their free-standing counterparts. This observation highlights the critical role of conductivity tuning in the design of shielding materials. In brief, the methodology presented here offers a viable route for systematically adjusting the porosity, mechanical properties, 3D spatial configuration, electrical conductivity, and shielding efficiency of aerogels. Such advancements open new horizons for their application in sophisticated designs and functionalities. Figure 7.28. (a) The electrical conductivity of the free-standing aerogel after thermal annealing at 800 °C for 1 h under Ar at different CNC loadings; (b) shielding parameters, (c) shielding coefficients, and (d) frequency-dependant shielding behavior (in the X-band, 8.2-12.4 GHz) of the free-standing aerogel with an increasing CNC content. (e) Shielding parameters, and (f) shielding coefficients of 3D printed thermally annealed GO1 CNC10 aerogels at different thicknesses. (g) Shielding mechanisms of thermally annealed (800 °C for 1 h under Ar) (I) free-standing and (II) 3D-printed aerogels. 210 Figure 7.29. EMI shielding performance of thermally annealed (a) GO1 CNC1, (b) GO1 CNC3, (c) GO1 CNC5, and (d) GO1 CNC10 free-standing aerogels within the X-band frequency range (8.2-12.4 GHz). Figure 7.30. EMI shielding performance of thermally annealed 3D printed grides of GO1 CNC10 with (a) 1 mm, (b) 3 mm, and (c) 4 mm thicknesses. 211 Table 7.6. The Shielding performance of the thermally annealed free-standing and 3D-printed aerogels. Shield Density (mg cm-3) Thickness (mm) Absorbance SET (dB) SSE/t (dB g-1 cm2) rFS GO1 CNC1 aerogel 2.63 10 0.59 51.59 19615.96 rFS GO1 CNC3 aerogel 4.44 10 0.54 78.26 17626.12 rFS GO1 CNC5 aerogel 6.11 10 0.47 78.77 12891.98 rFS GO1 CNC10 aerogel 11.70 10 0.42 79.46 6791.45 Reduced 3D-printed GO1 CNC10 aerogel - 1 0.31 16.78 - Reduced 3D-printed GO1 CNC10 aerogel - 3 0.41 21.31 - Reduced 3D-printed GO1 CNC10 aerogel ~12.13 4 0.27 38.24 7881.28 Abbreviations: reduced free-standing (rFS). 7.7. Conclusions This chapter unveils a tunable jammed emulsion gel system emerging from the electrostatic interactions between nanomaterials in the aqueous phase and ligands in the oil phase. These interactions forge emulsions with improved viscoelastic properties and enable 3D printing directly after undergoing post-jamming ionic crosslinking. Remarkably, this procedure is viable even at low ink concentrations, facilitating the formulation of inks with specific nanomaterial compositions. The process uniquely enables the fabrication of hierarchically porous monoliths featuring complex shapes and spatial configurations through the freezing and lyophilization of the 3D-printed ink. The methodology exploits the distinctive characteristics of nanomaterials to modify the mechanical attributes of the aerogels, where increasing the CNC loading transitions the aerogel from a flexible state to a stiffer one by varying the nanomaterial composition or through post-processing adjustments. Additionally, post-annealing treatments of the aerogels improved their shielding effectiveness, offering the capability to fine-tune absorptive or reflective properties by adjusting porosity and electrical conductivity. This innovative approach marks a significant advancement in aerogel fabrication, enabling precise control over their 3D spatial arrangement. 212 This opens up a plethora of possibilities for the design of advanced functional materials, enabling new avenues for innovative applications in various fields. 213 Chapter 8: Conclusions, Challenges & Future Prospects This thesis represents a significant advancement in the field of multi-scale porous engineerable aerogel manufacturing, achieved through the application of interfacial science for advanced functionalities, with a specific focus on EMI shielding. The research revolves around establishing a versatile aerogel manufacturing roadmap, transitioning from interfacially complexed structured liquid templates to multi-scale porous aerogels with tunable features across dimensions, spanning nano-scale chemistry, micro-scale interfacial assembly, and macro-scale manufacturing. This approach enables the customization of aerogels' composition, features, porosity, 3D spatial morphology, and physical/chemical properties to meet specific application requirements. The aerogels were fabricated in three primary morphological categories: (i) filamentous, (ii) free-standing, and (iii) 3D-printed aerogels. Each category underwent thorough optimization to enhance EM wave dissipation parameters, culminating in highly effective, absorption-dominant porous shielding constructs. The chapter starts with section 8.1, which provides a comprehensive summary of the achievements in each chapter, highlighting the critical challenges addressed by the methodologies employed. Section 8.2 outlines the technical challenges encountered throughout the research process and potential limitations to consider for future developments. Section 8.3 offers recommendations for future work, building on the foundation established by this thesis. This work lays a robust groundwork for the further development of multifunctional aerogels, pushing the boundaries of materials science and EMI shielding technologies. 8.1. Summary of main findings Chapter 3: This chapter summarizes the recipes and in-depth characterization of synthesized nanomaterials as the building blocks for aerogel manufacturing. These compounds include GO, 214 mGO, and CNF, specifically designed and processed based on the need for interfacial complexation. Examples of key specifications include the decoration of foundation nanomaterials like GO and CNF with active carboxylic acid functional groups and their high aspect ratio, making them promising for interfacial complexation and the formation of structured liquids as templates for aerogels manufacturing. The outcome of the characterizations showcased the excellent quality of the synthesized nanomaterials with the required features and characteristics. This chapter also provides a technical roadmap for precise and in-depth nanomaterial characteristics that can be used for a wide array of applications, including but not limited to EMI shielding, piezoresistive sensing, stimuli-responsive materials, oil absorption, thermal insulation, infrared radiation blocking, Joule-heating, and beyond. Chapter 4: This chapter introduces a versatile structured liquid templating approach toward manufacturing engineerable ultra-lightweight filamentous aerogels with on demand characteristics. The approach relies on the interfacial complexation of the carboxylic acid functionalized GO flakes with amine-terminated ligands at the oil/water interface, stabilizing the structured liquids in their non-equilibrium form. This was facilitated by the formation of nanoparticle surfactants (NPSs) and jamming of the nanoparticles at the interface, creating a robust interfacial-driven skin capable of overcoming the instabilities and preserving the integrity of the structured liquids. The promising integrity of the formed structured liquids allows customization of the nanomaterial composition upon hybridization with other compounds like mGO and CNF. The approach has a key advantage over existing methodologies, and that is control over the aerogel features from nano-scale chemistry and micro-scale interfacial complexation up to macro-scale aerogel manufacturing. This enabled the manufacturing of ultra-lightweight (3.05-3.41 mg cm-3) hierarchical macroscopic aerogels featuring multi-scale porosity combined with remarkable 215 compressibility (90%) and instant shape recovery upon compression and force release. This chapter was mainly dedicated to providing a comprehensive roadmap for aerogel design and in-depth characterization. This was accompanied by optimizing the liquid templating approach to tuning the features of the resulting aerogels toward advanced applications with a special focus on the design of absorption-dominant shielding systems. The optimization included the following key parameters: ✓ Composition: Selecting a wide range of nanomaterial compositions consisting of 1D or 2D nanomaterials for the manufacturing of structured liquid templates as the foundation for aerogel manufacturing. The considered compositions include GO, GO:mGO, and GO:CNF systems, which enable altering the features of aerogels for various applications. ✓ Porosity: Tuning the micro-scale porosity (the porous core within the filaments) and macro-scale porosity (the voids between the filaments) of aerogels on demand by adjusting the composition, selecting appropriate needle sizes (to modify filament diameter), and optimizing processing parameters. ✓ Electrical Conductivity and Magnetization: Adjusting the electrical conductivity and magnetic properties of the aerogels by tuning their composition during manufacturing. This provides the possibility of altering the shielding behaviour when combined with porosity engineering. The introduction of magnetization also makes the structured liquids or their resulting aerogels responsive to an external magnetic field, enabling stimuli-responsiveness. Key challenges addressed in Chapter 4: The addressed key challenges include: i) designing and optimizing a versatile aerogel engineering approach with the ability to control their features across scales, ii) addressing the challenge associated with the poor mechanical integrity of aerogels by 216 making highly flexible aerogels, iii) altering the 3D spatial morphology on demand, iv) applying custom composition, features, and functions to the aerogels based on the necessities required by advance applications. Chapter 5: In this chapter, I leveraged the optimized structured liquid templating approach for aerogel manufacturing to explore their potential and engineerability for advanced applications. The resulting aerogels were tailored to address a wide range of applications, including: i) EMI shielding with the ability to switch between reflective and absorptive characteristics on demand, ii) oil absorption and oil/water separation, achieving exceptional absorption capacity, iii) piezoresistive sensing for monitoring mechanical or human motion, and iv) thermal insulation, infrared radiation shielding, and Joule heating, showcasing versatile energy management capabilities. The ability of design customization allowed engineering the features of liquid templates toward controllable shielding characteristics with absorptive or reflective mechanisms on demand. The developed ultra-lightweight reduced aerogels made of GO, GO-Fe, and GO-CNF showcased high specific shielding effectiveness over thickness (SSE/t) ranging from 31739 to 39893 dB cm2 g-1. Such a breakthrough in shielding design was a motivation that made the resulting experimental paper be selected as the cover photo in the Journal of Advanced Materials (Figure 8.1). Additionally, during the dual reduction process, viz., initial chemical reduction followed by thermal annealing, the GO aerogels were transformed into formidable recoverable oil absorption tools. The double-reduced filamentous GO aerogel showcased a record-high oil absorption rate for various types of oils or organic solvents through a very fast absorption kinetics. The recoverability of the aerogel through simple squeezing made them promising for scalable oil/water separation and recovery applications. 217 The flexibility and proper electrical conductivity within the multi-scale porous structure of reduced GO-CNF aerogels made them promising candidates for piezoresistive sensing. The assembled structure showcased high sensitivity toward human motion monitoring with a fast response/recovery time (525/350 ms). Such a multi-scale porous conductive framework also showed potential for effective thermal insulation and blocking infrared radiations, rendering them potential building blocks for effective energy management. Applying a low DC voltage to the reduced GO-CNF aerogel enabled the preparation of a potent Joule heater with instant heating-cooling capability in about 3 seconds. These outcomes vividly illuminate the potential of liquid templating toward pushing the boundaries of aerogels for task-oriented functional designs. Key challenges addressed in Chapter 5: This chapter addressed several key challenges, including the development of a comprehensive roadmap for fabricating functional aerogels capable of meeting diverse technological demands. It also tackled the critical issue of creating absorption-dominant shielding constructs or shielding systems with controllable properties. This was achieved by fine-tuning the EM wave dissipating parameters within the aerogel building blocks, enabling precise control over their shielding behavior. 218 Figure 8.1. Feature cover image of Journal of Advanced Materials, highlighting the potential of liquid-templating aerogels approach in developing efficient multi-scale porous shielding systems. The cover photo is related to one of my main experimental papers 109, published with the DOI number 10.1002/adma.202370299. 219 Chapter 6: This chapter includes a breakthrough in shielding systems by introducing the concept of “aerogel electromagnetic traps”. The concept includes manufacturing anti-reflection aerogels with the capability to attenuate the incident EM waves and secondary reflected ones from the surface of highly metallic substrates, addressing two of the major challenges in shielding science. Benefiting from the engineerable nature of the liquid templating approach, I adjusted the size of the filaments during extrusion to improve the interacting interfaces of reduced filamentous rGO-CNF aerogels with the EM waves. This facilitated the impedance matching and allowed the EM waves to penetrate through and interact with the aerogel’s interior porosities and interfaces. The impedance matching, combined with enhanced multiple internal scattering and dielectric and conduction losses, turns the resulting aerogel into a potent absorption-dominant shielding system capable of attenuating EM waves’ energy in the form of heat and minimizing surface reflections. When paired with metallic substrates made of highly conductive materials such as Al, Cu, Ti, and Zn, the flexible anti-reflection ultra-lightweight aerogels (density: 3.12–3.40 mg cm-3) shifted the total shielding mechanism from reflection-dominant to absorption-dominant across all cases. The paired aerogel-metal systems demonstrated absorbance values ranging from 0.70 to 0.81 and total shielding effectiveness between 53 and 89 dB within the X-band frequency range (8.2–12.4 GHz). These results vividly highlight the efficacy of the aerogel electromagnetic trap concept in transforming reflection-dominant, highly conductive shields into powerful absorption-dominant shielding systems. The experimental study detailing this concept was featured as the cover photo of the Journal of Nanoscale (Figure 8.2). Key challenges addressed in Chapter 6: The outcome of this part addresses two of the long-lasting and major challenges in the shielding science: i) the requirement to develop lightweight, mechanically robust, and absorption-dominant shielding systems with high total shielding 220 effectiveness, and ii) blocking the surface reflection of highly conductive substrates and turning them into potent absorption-dominant shielding systems. Figure 8.2. The feature cover photo of the Journal of Nanoscale, showing the potential of filamentous aerogels in blocking the incident and secondary reflected EM waves from the surface of metallic substrates. The cover photo is related to one of my main experimental papers 355, which was included in the main paper published with the DOI number of 10.1039/d3nr06478f. 221 Chapter 7: In this chapter, I developed an oil-in-water (O/W) emulsion-templated aerogel manufacturing approach with the ability to tune the viscoelastic and rheological characteristics of the gels upon post-jamming ionic crosslinking with NaHCO3. This approach enables the fabrication of multi-scale porous free-standing aerogels or high-precision 3D-printed aerogels via direct ink writing (DIW), offering precise control over their 3D macroscopic spatial morphology and allowing the creation of complex geometries. Beyond this advantage, the technique also allows for the tuning of the mechanical properties and shielding mechanisms of the resulting aerogels by altering their composition. Specifically, by adjusting the composition of the building blocks, using fixed graphene oxide (GO) content and variable cellulose nanocrystal (CNC) concentrations with or without post-processing, it is possible to engineer the mechanical properties of the ultra-lightweight aerogels to range from flexible to stiff (elastic modulus up to 0.45 MPa) as required. The engineerability of the design allowed for tailoring the specific electromagnetic shielding effectiveness from 6791 to 19615 dB cm² g-1 by simple CNC content variation, highlighting the versatility of the approach. This technique enables the exploration of numerous jammed formulations through emulsion templating toward advanced functions by considering the mechanical properties and structural integrity. Key challenges addressed in Chapter 7: This chapter addressed several key challenges in aerogel manufacturing: i) designing a jammed O/W emulsion-templating approach toward customization and engineering of design, ii) altering the viscoelastic properties of the jammed emulsion gels via ionic crosslinking without interrupting the jammed assembly, iii) 3D printing the post-jamming ionically crosslinked O/W emulsion gels, enabling formation of complex geometries, iv) controlling the mechanical properties of aerogels, making flexible or stiff porous constructs on 222 demand, and v) controlling the shielding mechanism and specific shielding effectiveness of the aerogels through simple composition alteration. 8.2. Technical challenges This section outlines and discusses the technical challenges I encountered during the aerogel manufacturing process and potential limitations for future development, which are categorized as follows: Structured liquids: One significant challenge in forming filamentous structured liquids is the necessity of adding graphene oxide (GO) to the ink composition. Other compounds, such as cellulose nanofibers (CNF) and modified graphene oxide (mGO), lack the ability to form robust, stable, and non-equilibrium-shaped structured liquids with high integrity. This limitation requires a hybrid ink composition that includes GO due to its 2D morphology and amphiphilic nature, which are advantageous for interfacial complexation. Achieving optimally structured liquids involved identifying the proper processing parameters and ink composition to serve as effective templates for aerogel manufacturing. Aerogel manufacturing: Several challenges arose during the aerogel manufacturing phase following the formation of structured liquids. Material concentration: Low material concentrations (<5 mg mL⁻¹) resulted in mechanically weak porous constructs. A concentration range of 8–10 mg mL⁻1 was essential to achieve robust cell walls within the aerogel building blocks. Freezing and lyophilization: Improper freezing techniques and insufficient time for ice crystal formation (less than 12–24 hours at -85 °C) could degrade the aerogel’s properties. Subsequent lyophilization required precise timing, as even minimal moisture remnants could compromise flexibility and create issues during thermal annealing. 223 Thermal annealing: The thermal annealing step posed challenges such as improper sealing of the quartz tube, inconsistent vacuum rates, and inaccurate gas flow control, all of which could adversely affect the aerogel's electrical conductivity and EMI shielding performance. Additionally, residual moisture from insufficient freeze-drying could destroy the aerogel structure during high-temperature annealing, emphasizing the need for thorough pre-drying. Aerogel’s reflective nature: Electrically conductive porous materials like aerogels are designed to dissipate EM wave energy through heat and increase wave absorbance. However, suboptimal electrical conductivity can cause excessive surface reflections, transforming the aerogel into a reflection-dominant shielding material. Optimizing electrical conductivity and impedance matching is critical to ensuring effective EM wave penetration and dissipation through internal scattering and combined dielectric, conduction, and magnetic losses. These challenges underscore the importance of meticulous optimization in structured liquid formation, composition adjustment, processing techniques, and aerogel design to achieve the desired mechanical, thermal, and electromagnetic properties. Scalability and cost consideration: One of the important measures during the production of aerogels is their adaptability with mass-scale production approaches, with a minimized production cost toward crucial societal demand in various disciplines. Reaching this aim requires following simple molding methods and gelation, followed by providing the possibility of drying at room temperature after initial freezing. This requires strengthening the cell walls to avoid shrinkage and structural collapse during drying. From an economic standpoint, developing aerogels from sustainable building blocks, such as cellulose derivatives or readily available industrial-scale raw materials, is advantageous for minimizing overall fabrication costs. 224 Mechanical and environmental stability: Another critical parameter is the stability of aerogels under cyclic mechanical loading and environmental factors such as humidity and temperature fluctuations. Enhancing cyclic stability requires the development of resilient aerogels composed of robust supporting building blocks, such as graphene oxide (GO), to reinforce the cell walls and preserve structural integrity under repeated stress. However, achieving the level of stability demanded by advanced applications necessitates further enhancement of current systems through the integration of more durable materials, such as polyurethane or polydimethylsiloxane (PDMS). In their non-reduced form, aerogels remain vulnerable to environmental variations. Controlled reduction processes, either single or double-step, using GO under inert atmospheres (e.g., argon or nitrogen) can render the aerogels hydrophobic and more resistant to humidity and thermal stress. Additionally, post-treatment with hydrophobic agents or encapsulation within resilient resins, such as epoxy or PDMS, can further improve environmental resistance, ensuring long-term and reliable performance. 8.3. Future works recommendation Considering the extensive potential of interfacial complexation for customizing designs for advanced functionalities, I propose the following pathways to further advance this research: ✓ Altering the nanoparticle surfactant systems: One recommendation for further research is to discover novel nanoparticle and/or ligand choices to generate robust interfacially driven assemblies. This provides the possibility of creating functional porous constructs with on demand features. This design alteration could also be accompanied by stimuli responsiveness, leading to smart and controllable jammed structured liquids. ✓ Exploring the potential of jammed emulsion systems: The oil-in-water (O/W) or water-in-oil (W/O) emulsion systems made by the jamming of nanoparticles at the oil/water 225 interface provide great opportunities to tune their rheological characteristics toward the requirement of 3D printing techniques through direct ink writing (DIW) or liquid-in-liquid printing. This could be done through the selection of novel ligands or ionic complexation to facilitate the enhancement of viscoelastic properties. Such an advantage provides the possibility to 3D print the aerogel template prior to freezing and lyophilization, enabling on demand 3D spatial morphology adjustment or formation of complex customized geometries through computer-guided design. ✓ Studying the effective parameters of interfacial complexation: The interfacial complexation or nanoparticles jamming at the interface is affectable by several parameters like i) nanoparticles or ligands concentration, ii) pH of the medium, iii) ionic strength, iv) nanoparticle size, and v) polymeric ligands’ molecular weight. Hence, a very interesting idea to pursue research is to experimentally review and study the effect of governing parameters on structured liquids, their formation, and structural integrity. This provides a clearer experimental roadmap for researchers to push the boundaries of interfacial science toward advanced functions. ✓ Exploring artificial intelligence and molecular simulation potentials: The advancement in artificial intelligence (AI) and molecular simulation provides a lot of opportunities to study interfacially driven systems. This enables the discovery of possible novel complexation systems, like the case of Bijels, which was first predicted by simulation studies and then experimentally practiced. Additionally, simulation or AI tools provide the opportunity to study the governing parameters of the jamming systems, thereby allowing pre-optimization to obtain the best complexation systems. 226 ✓ Improving the mechanical strength of aerogels by minimizing payload: Soft porous materials like aerogels suffer from inadequate mechanical strength, or in some cases, showcasing weak brittle structures. To this end, developing techniques to enhance the mechanical strength of aerogels while minimizing their payload is required. Strengthening the aerogel cell walls through novel formulations or incorporating robust supporting scaffolds, such as polyimide, aramid nanofibers, chitin, or similar materials, could significantly improve the mechanical robustness of the resulting constructs. These advancements would enable porous aerogels to withstand practical working conditions, broadening their applicability in real-world scenarios. ✓ Exploring novel electromagnetic trap systems: An in-depth understanding of the most effective EM wave dissipating parameters, such as dielectric loss, magnetic loss, conduction loss, and multiple internal scattering induced by porous arrangements, can facilitate the design of highly efficient EM wave dissipators. To advance this field, I recommend exploring innovative aerogel-based EM trapping systems that minimize surface reflections through impedance matching, combined with porous constructs containing numerous interfaces that amplify EM wave dissipation. Promising directions include: i) Multi-layered shielding structures: designing aerogels with layered compositions to optimize the distribution of EM wave dissipation mechanisms, ii) gradient electrical conductivity: engineering aerogels with conductivity gradients to enhance impedance matching and maximize absorption, and iii) aligned microscale porosities: utilizing directional freezing techniques to create aerogels with aligned porosities, enriched with conductive and/or magnetic materials for improved wave dissipation. 227 Bibliography 1. Jaeger, H. M., Celebrating soft matter’s 10th anniversary: toward jamming by design. Soft Matter 2015, 11 (1), 12-27. 2. Liu, A. J.; Nagel, S. R., Jamming is not just cool any more. Nature 1998, 396 (6706), 21-22. 3. Li, L.; Deng, Z.; Chen, M.; Yu, Z. Z.; Russell, T. P.; Zhang, H. B., 3D printing of ultralow-concentration 2D nanomaterial inks for multifunctional architectures. Nano Letters 2022, 23 (1), 155-162. 4. Shi, S.; Russell, T. P., Nanoparticle assembly at liquid–liquid interfaces: from the nanoscale to mesoscale. Advanced Materials 2018, 30 (44), 1800714. 5. Gu, P.; Luo, X.; Zhou, S.; Wang, D.; Li, Z.; Chai, Y.; Zhang, Y.; Shi, S.; Russell, T. P., Stabilizing liquids using interfacial supramolecular assemblies. Angewandte Chemie International Edition 2023, 62 (36), e202303789. 6. Wu, B.; Yang, C.; Xin, Q.; Kong, L.; Eggersdorfer, M.; Ruan, J.; Zhao, P.; Shan, J.; Liu, K.; Chen, D., Attractive Pickering emulsion gels. Advanced Materials 2021, 33 (33), 2102362. 7. Kamkar, M.; Ghaffarkhah, A.; Ajdary, R.; Lu, Y.; Ahmadijokani, F.; Mhatre, S. E.; Erfanian, E.; Sundararaj, U.; Arjmand, M.; Rojas, O. J., Structured ultra‐flyweight aerogels by interfacial complexation: self‐assembly enabling multiscale designs. Small 2022, 18 (20), 2200220. 8. Shi, S.; Liu, X.; Li, Y.; Wu, X.; Wang, D.; Forth, J.; Russell, T. P., Liquid letters. Advanced Materials 2018, 30 (9), 1705800. 9. Huang, C.; Forth, J.; Wang, W.; Hong, K.; Smith, G. S.; Helms, B. A.; Russell, T. P., Bicontinuous structured liquids with sub-micrometre domains using nanoparticle surfactants. Nature Nanotechnology 2017, 12 (11), 1060-1063. 10. Cui, M.; Emrick, T.; Russell, T. P., Stabilizing liquid drops in nonequilibrium shapes by the interfacial jamming of nanoparticles. Science 2013, 342 (6157), 460-463. 11. Huang, C.; Cui, M.; Sun, Z.; Liu, F.; Helms, B. A.; Russell, T. P., Self-regulated nanoparticle assembly at liquid/liquid interfaces: a route to adaptive structuring of liquids. Langmuir 2017, 33 (32), 7994-8001. 12. Yao, H.; Momozawa, O.; Hamatani, T.; Kimura, K., Phase transfer of gold nanoparticles across a water/oil interface by stoichiometric ion-pair formation on particle surfaces. Bulletin of the Chemical Society of Japan 2000, 73 (12), 2675-2678. 13. Chen, S.; Yao, H.; Kimura, K., Reversible transference of Au nanoparticles across the water and toluene interface: a Langmuir type adsorption mechanism. Langmuir 2001, 17 (3), 733-739. 14. Kurth, D. G.; Lehmann, P.; Lesser, C., Engineering the surface chemical properties of semiconductor nanoparticles: surfactant-encapsulated CdTe-clusters. Chemical Communications 2000, (11), 949-950. 228 15. Yao, H.; Momozawa, O.; Hamatani, T.; Kimura, K., Stepwise size-selective extraction of carboxylate-modified gold nanoparticles from an aqueous suspension into toluene with tetraoctylammonium cations. Chemistry of Materials 2001, 13 (12), 4692-4697. 16. Feng, T.; Hoagland, D. A.; Russell, T. P., Assembly of acid-functionalized single-walled carbon nanotubes at oil/water interfaces. Langmuir 2014, 30 (4), 1072-1079. 17. Feng, T.; Hoagland, D. A.; Russell, T. P., Interfacial rheology of polymer/carbon nanotube films co-assembled at the oil/water interface. Soft Matter 2016, 12 (42), 8701-8709. 18. Huang, C.; Sun, Z.; Cui, M.; Liu, F.; Helms, B. A.; Russell, T. P., Structured liquids with pH‐triggered reconfigurability. Advanced Materials 2016, 28 (31), 6612-6618. 19. Chai, Y.; Lukito, A.; Jiang, Y.; Ashby, P. D.; Russell, T. P., Fine-tuning nanoparticle packing at water–oil interfaces using ionic strength. Nano Letters 2017, 17 (10), 6453-6457. 20. Binks, B. P.; Rodrigues, J. A.; Frith, W. J., Synergistic interaction in emulsions stabilized by a mixture of silica nanoparticles and cationic surfactant. Langmuir 2007, 23 (7), 3626-3636. 21. Binks, B. P.; Rodrigues, J. A., Enhanced stabilization of emulsions due to surfactant-induced nanoparticle flocculation. Langmuir 2007, 23 (14), 7436-7439. 22. Lin, D.; Liu, T.; Yuan, Q.; Yang, H.; Ma, H.; Shi, S.; Wang, D.; Russell, T. P., Stabilizing aqueous three-dimensional printed constructs using chitosan-cellulose nanocrystal assemblies. ACS Applied Materials & Interfaces 2020, 12 (49), 55426-55433. 23. Xu, R.; Liu, T.; Sun, H.; Wang, B.; Shi, S.; Russell, T. P., Interfacial assembly and jamming of polyelectrolyte surfactants: A simple route to print liquids in low-viscosity solution. ACS Applied Materials & Interfaces 2020, 12 (15), 18116-18122. 24. Kamkar, M.; Erfanian, E.; Bazazi, P.; Ghaffarkhah, A.; Sharif, F.; Xie, G.; Kannan, A.; Arjmand, M.; Hejazi, S. H.; Russell, T. P., Interfacial assembly of graphene oxide: from super elastic interfaces to liquid‐in‐liquid printing. Advanced Materials Interfaces 2022, 9 (6), 2101659. 25. Ghaffarkhah, A.; Hashemi, S. A.; Rostami, S.; Amini, M.; Ahmadijokani, F.; Pournaghshband Isfahani, A.; Mhatre, S. E.; Rojas, O. J.; Kamkar, M.; Wuttke, S., Ultra‐flyweight cryogels of MXene/graphene oxide for electromagnetic interference shielding. Advanced Functional Materials 2023, 33 (50), 2304748. 26. Forth, J.; Liu, X.; Hasnain, J.; Toor, A.; Miszta, K.; Shi, S.; Geissler, P. L.; Emrick, T.; Helms, B. A.; Russell, T. P., Reconfigurable printed liquids. Advanced Materials 2018, 30 (16), 1707603. 27. Feng, W.; Chai, Y.; Forth, J.; Ashby, P. D.; Russell, T. P.; Helms, B. A., Harnessing liquid-in-liquid printing and micropatterned substrates to fabricate 3-dimensional all-liquid fluidic devices. Nature Communications 2019, 10 (1), 1-9. 28. Xie, X.; Xu, Z.; Yu, X.; Jiang, H.; Li, H.; Feng, W., Liquid-in-liquid printing of 3D and mechanically tunable conductive hydrogels. Nature Communications 2023, 14 (1), 4289. 29. Liu, X.; Shi, S.; Li, Y.; Forth, J.; Wang, D.; Russell, T. P., Liquid tubule formation and stabilization using cellulose nanocrystal surfactants. Angewandte Chemie 2017, 129 (41), 12768-12772. 229 30. Toor, A.; Helms, B. A.; Russell, T. P., Effect of nanoparticle surfactants on the breakup of free-falling water jets during continuous processing of reconfigurable structured liquid droplets. Nano Letters 2017, 17 (5), 3119-3125. 31. Zhang, Y.; Zhu, G.; Dong, B.; Wang, F.; Tang, J.; Stadler, F. J.; Yang, G.; Hong, S.; Xing, F., Interfacial jamming reinforced Pickering emulgel for arbitrary architected nanocomposite with connected nanomaterial matrix. Nature Communications 2021, 12 (1), 111. 32. Pickering, S. U., Cxcvi. Journal of Chemical Society, Transactions 1907, 91 (0), 2001-2021. 33. Binks, B. P., Particles as surfactants—similarities and differences. Current Opinion in Colloid & Interface Science 2002, 7 (1-2), 21-41. 34. Aveyard, R.; Binks, B. P.; Clint, J. H., Emulsions stabilised solely by colloidal particles. Advances in Colloid and Interface Science 2003, 100, 503-546. 35. Finkle, P.; Draper, H. D.; Hildebrand, J. H., The theory of emulsification1. Journal of the American Chemical Society 1923, 45 (12), 2780-2788. 36. Schulman, J. H.; Leja, J., Control of contact angles at the oil-water-solid interfaces. Emulsions stabilized by solid particles (BaSO4). Transactions of the Faraday Society 1954, 50, 598-605. 37. Liu, Y.; Xu, Z.; Gao, W.; Cheng, Z.; Gao, C., Graphene and other 2D colloids: liquid crystals and macroscopic fibers. Advanced Materials 2017, 29 (14), 1606794. 38. Naficy, S.; Jalili, R.; Aboutalebi, S. H.; Gorkin III, R. A.; Konstantinov, K.; Innis, P. C.; Spinks, G. M.; Poulin, P.; Wallace, G. G., Graphene oxide dispersions: tuning rheology to enable fabrication. Materials Horizons 2014, 1 (3), 326-331. 39. Chen, D. T.; Wen, Q.; Janmey, P. A.; Crocker, J. C.; Yodh, A. G., Rheology of soft materials. Annual Review of Condensed Matter Physics 2010, 1 (1), 301-322. 40. Shi, S.; Qian, B.; Wu, X.; Sun, H.; Wang, H.; Zhang, H. B.; Yu, Z. Z.; Russell, T. P., Self‐assembly of MXene‐surfactants at liquid–liquid interfaces: from structured liquids to 3D aerogels. Angewandte Chemie International Edition 2019, 58 (50), 18171-18176. 41. Sun, Z.; Feng, T.; Russell, T. P., Assembly of graphene oxide at water/oil interfaces: tessellated nanotiles. Langmuir 2013, 29 (44), 13407-13413. 42. Zhu, S.; Xie, G.; Cui, H.; Li, Q.; Forth, J.; Yuan, S.; Tian, J.; Pan, Y.; Guo, W.; Chai, Y., Aquabots. ACS Nano 2022, 16 (9), 13761-13770. 43. Rapp, B. E., Microfluidics: modeling, mechanics and mathematics. Elsevier: 2022. 44. Breslouer, O., Rayleigh-plateau instability: falling jet. Project Report 2010. 45. Cates, M. E.; Clegg, P. S., Bijels: a new class of soft materials. Soft Matter 2008, 4 (11), 2132-2138. 46. Mohraz, A., Interfacial routes to colloidal gelation. Current Opinion in Colloid & Interface Science 2016, 25, 89-97. 47. Mohraz, A., Simple shaking yields bicontinuity. Nature Nanotechnology 2017, 12 (11), 1021-1022. 230 48. Reeves, M.; Brown, A.; Schofield, A. B.; Cates, M.; Thijssen, J., Particle-size effects in the formation of bicontinuous Pickering emulsions. Physical Review E 2015, 92 (3), 032308. 49. Reeves, M.; Stratford, K.; Thijssen, J. H., Quantitative morphological characterization of bicontinuous Pickering emulsions via interfacial curvatures. Soft Matter 2016, 12 (18), 4082-4092. 50. Jhawat, V.; Gulia, M.; Sharma, A. K., Pseudoternary phase diagrams used in emulsion preparation. In Chemoinformatics and Bioinformatics in the Pharmaceutical Sciences, Elsevier: 2021; pp 455-481. 51. Ahmad, J.; Amin, S.; Kohli, K.; Mir, S. R., Construction of pseudoternary phase diagram and its evaluation: development of self-dispersible oral formulation. International Journal of Drug Development & Research 2013, 5 (2), 84-90. 52. Gradzielski, M.; Duvail, M.; de Molina, P. M.; Simon, M.; Talmon, Y.; Zemb, T., Using microemulsions: formulation based on knowledge of their mesostructure. Chemical Reviews 2021, 121 (10), 5671-5740. 53. Ghaffarkhah, A.; Kamkar, M.; Riazi, H.; Hosseini, E.; Dijvejin, Z. A.; Golovin, K.; Soroush, M.; Arjmand, M., Scalable manufacturing of flexible and highly conductive Ti3C2Tx/PEDOT: PSS thin films for electromagnetic interference shielding. New Journal of Chemistry 2021, 45 (44), 20787-20799. 54. Kamkar, M.; Ghaffarkhah, A.; Hosseini, E.; Amini, M.; Ghaderi, S.; Arjmand, M., Multilayer polymeric nanocomposites for electromagnetic interference shielding: fabrication, mechanisms, and prospects. New Journal of Chemistry 2021, 45, 21488-21507. 55. Amini, M.; Kamkar, M.; Rahmani, F.; Ghaffarkhah, A.; Ahmadijokani, F.; Arjmand, M., Multilayer structures of a Zn0.5Ni0.5Fe2O4-reduced graphene oxide/PVDF nanocomposite for tunable and highly efficient microwave absorbers. ACS Applied Electronic Materials 2021. 56. Jaroszewski, M.; Thomas, S.; Rane, A. V., Advanced Materials for Electromagnetic Shielding: Fundamentals, Properties, and Applications. 2018. 57. Aswathi, M.; Rane, A. V.; Ajitha, A.; Thomas, S.; Jaroszewski, M., EMI shielding fundamentals. Advanced Materials for Electromagnetic Shielding: Fundamentals, Properties, and Applications 2018, 1-9. 58. Shen, B.; Li, Y.; Zhai, W.; Zheng, W., Compressible graphene-coated polymer foams with ultralow density for adjustable electromagnetic interference (EMI) shielding. ACS Applied Materials & Interfaces 2016, 8 (12), 8050-8057. 59. Li, Q.; Chen, L.; Ding, J.; Zhang, J.; Li, X.; Zheng, K.; Zhang, X.; Tian, X., Open-cell phenolic carbon foam and electromagnetic interference shielding properties. Carbon 2016, 104, 90-105. 60. Iqbal, A.; Sambyal, P.; Koo, C. M., 2D MXenes for electromagnetic shielding: a review. Advanced Functional Materials 2020, 30 (47), 2000883. 61. Ott, H. W., Electromagnetic compatibility engineering. John Wiley & Sons: 2011. 62. Han, M.; Yin, X.; Hantanasirisakul, K.; Li, X.; Iqbal, A.; Hatter, C. B.; Anasori, B.; Koo, C. M.; Torita, T.; Soda, Y., Anisotropic MXene aerogels with a mechanically tunable ratio 231 of electromagnetic wave reflection to absorption. Advanced Optical Materials 2019, 7 (10), 1900267. 63. Lee, S. H.; Yu, S.; Shahzad, F.; Kim, W. N.; Park, C.; Hong, S. M.; Koo, C. M., Density-tunable lightweight polymer composites with dual-functional ability of efficient EMI shielding and heat dissipation. Nanoscale 2017, 9 (36), 13432-13440. 64. Ghaffarkhah, A.; Kamkar, M.; Dijvejin, Z. A.; Riazi, H.; Ghaderi, S.; Golovin, K.; Soroush, M.; Arjmand, M., High-resolution extrusion printing of Ti3C2-based inks for wearable human motion monitoring and electromagnetic interference shielding. Carbon 2022, 191, 277-289. 65. Isari, A. A.; Ghaffarkhah, A.; Hashemi, S. A.; Wuttke, S.; Arjmand, M., Structural design for EMI shielding: from underlying mechanisms to common pitfalls. Advanced Materials 2024, 36 (24), 2310683. 66. Anasori, B.; Gogotsi, Û. G., 2D metal carbides and nitrides (MXenes). Springer: 2019. 67. Schulz, R. B.; Plantz, V.; Brush, D., Shielding theory and practice. IEEE Transactions on Electromagnetic Compatibility 1988, 30 (3), 187-201. 68. Singh, A. P.; Mishra, M.; Sambyal, P.; Gupta, B. K.; Singh, B. P.; Chandra, A.; Dhawan, S., Encapsulation of γ-Fe2O3 decorated reduced graphene oxide in polyaniline core–shell tubes as an exceptional tracker for electromagnetic environmental pollution. Journal of Materials Chemistry A 2014, 2 (10), 3581-3593. 69. González, M.; Pozuelo, J.; Baselga, J., Electromagnetic shielding materials in GHz range. The Chemical Record 2018, 18 (7-8), 1000-1009. 70. Shahzad, F.; Alhabeb, M.; Hatter, C. B.; Anasori, B.; Hong, S. M.; Koo, C. M.; Gogotsi, Y., Electromagnetic interference shielding with 2D transition metal carbides (MXenes). Science 2016, 353 (6304), 1137-1140. 71. Sohi, N.; Rahaman, M.; Khastgir, D., Dielectric property and electromagnetic interference shielding effectiveness of ethylene vinyl acetate‐based conductive composites: Effect of different type of carbon fillers. Polymer Composites 2011, 32 (7), 1148-1154. 72. Kumar, R.; Choudhary, H. K.; Pawar, S. P.; Bose, S.; Sahoo, B., Carbon encapsulated nanoscale iron/iron-carbide/graphite particles for EMI shielding and microwave absorption. Physical Chemistry Chemical Physics 2017, 19 (34), 23268-23279. 73. Yang, M.; Jia, X.; He, D.; Ma, Y.; Cheng, Y.; Wang, J.; Li, Y.; Wang, C., Superhydrophobic and corrosion-resistant electrospun hybrid membrane for high-efficiency electromagnetic interference shielding. ACS Applied Electronic Materials 2021, 3 (5), 2067-2078. 74. Im, J. S.; Kim, J. G.; Lee, S. H.; Lee, Y. S., Enhanced adhesion and dispersion of carbon nanotube in PANI/PEO electrospun fibers for shielding effectiveness of electromagnetic interference. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2010, 364 (1-3), 151-157. 75. Guo, H.; Zheng, M.; Ma, X.; Cao, R.; Liu, K.; Yang, W.; Jian, S.; Jiang, S.; Duan, G., Electrospun TaC/Fe3C–Fe carbon composite fabrics for high efficiency of electromagnetic interference shielding. Composites Communications 2022, 31, 101130. 232 76. Ji, H.; Zhao, R.; Zhang, N.; Jin, C.; Lu, X.; Wang, C., Lightweight and flexible electrospun polymer nanofiber/metal nanoparticle hybrid membrane for high-performance electromagnetic interference shielding. NPG Asia Materials 2018, 10 (8), 749-760. 77. Zong, Z.; Ren, P.; Guo, Z.; Wang, J.; Chen, Z.; Jin, Y.; Ren, F., Three-dimensional macroporous hybrid carbon aerogel with heterogeneous structure derived from MXene/cellulose aerogel for absorption-dominant electromagnetic interference shielding and excellent thermal insulation performance. Journal of Colloid and Interface Science 2022, 619, 96-105. 78. Zeng, Z.; Wu, T.; Han, D.; Ren, Q.; Siqueira, G.; Nyström, G., Ultralight, flexible, and biomimetic nanocellulose/silver nanowire aerogels for electromagnetic interference shielding. ACS Nano 2020, 14 (3), 2927-2938. 79. Hou, Y.; Cheng, L.; Zhang, Y.; Du, X.; Zhao, Y.; Yang, Z., High temperature electromagnetic interference shielding of lightweight and flexible ZrC/SiC nanofiber mats. Chemical Engineering Journal 2021, 404, 126521. 80. Zhang, Y.; Ruan, K.; Gu, J., Flexible sandwich‐structured electromagnetic interference shielding nanocomposite films with excellent thermal conductivities. Small 2021, 17 (42), 2101951. 81. Kistler, S. S., Coherent expanded aerogels and jellies. Nature 1931, 127 (3211), 741-741. 82. Hüsing, N.; Schubert, U., Aerogels—airy materials: chemistry, structure, and properties. Angewandte Chemie International Edition 1998, 37 (1‐2), 22-45. 83. Parale, V. G.; Lee, K. Y.; Park, H. H.; Parale, V. G.; Lee, K. Y.; Park, H. H., Flexible and transparent silica aerogels: An overview. Journal of the Korean Ceramic Society 2017, 54 (3), 184-199. 84. Kanamori, K.; Nakanishi, K., Controlled pore formation in organotrialkoxysilane-derived hybrids: from aerogels to hierarchically porous monoliths. Chemical Society Reviews 2011, 40 (2), 754-770. 85. Ciriminna, R.; Fidalgo, A.; Pandarus, V.; Beland, F.; Ilharco, L. M.; Pagliaro, M., The sol–gel route to advanced silica-based materials and recent applications. Chemical Reviews 2013, 113 (8), 6592-6620. 86. Yang, J.; Li, Y.; Zheng, Y.; Xu, Y.; Zheng, Z.; Chen, X.; Liu, W., Versatile aerogels for sensors. Small 2019, 15 (41), 1902826. 87. Mao, J.; Iocozzia, J.; Huang, J.; Meng, K.; Lai, Y.; Lin, Z., Graphene aerogels for efficient energy storage and conversion. Energy & Environmental Science 2018, 11 (4), 772-799. 88. Jin, R.; Zhou, Z.; Liu, J.; Shi, B.; Zhou, N.; Wang, X.; Jia, X.; Guo, D.; Xu, B., Aerogels for thermal protection and their application in aerospace. Gels 2023, 9 (8), 606. 89. Parale, V. G.; Kim, T.; Choi, H.; Phadtare, V. D.; Dhavale, R. P.; Kanamori, K.; Park, H. H., Mechanically strengthened aerogels through multiscale, multicompositional, and multidimensional approaches: A Review. Advanced Materials 2024, 36 (18), 2307772. 90. Bokov, D.; Turki Jalil, A.; Chupradit, S.; Suksatan, W.; Javed Ansari, M.; Shewael, I. H.; Valiev, G. H.; Kianfar, E., Nanomaterial by sol‐gel method: synthesis and application. Advances in Materials Science and Engineering 2021, 2021 (1), 5102014. 233 91. Ferreira, E. S.; Rezende, C. A.; Cranston, E. D., Fundamentals of cellulose lightweight materials: bio-based assemblies with tailored properties. Green Chemistry 2021, 23 (10), 3542-3568. 92. Huang, L.; Yang, J.; Zhao, Y.; Miyata, H.; Han, M.; Shuai, Q.; Yamauchi, Y., Monolithic covalent organic frameworks with hierarchical architecture: attractive platform for contaminant remediation. Chemistry of Materials 2023, 35 (7), 2661-2682. 93. Li, C.; Qiu, L.; Zhang, B.; Li, D.; Liu, C. Y., Robust vacuum‐/air‐dried graphene aerogels and fast recoverable shape‐memory hybrid foams. Advanced Materials 2016, 28 (7), 1510-1516. 94. Yang, H.; Li, Z.; Sun, G.; Jin, X.; Lu, B.; Zhang, P.; Lin, T.; Qu, L., Superplastic air‐dryable graphene hydrogels for wet‐press assembly of ultrastrong superelastic aerogels with infinite macroscale. Advanced Functional Materials 2019, 29 (26), 1901917. 95. Gizli, N.; Çok, S. S.; Koç, F., Aerogel, xerogel, and cryogel: synthesis, surface chemistry, and properties—practical environmental applications and the future developments. In Advanced Materials for Sustainable Environmental Remediation, Elsevier: 2022; pp 195-229. 96. Françon, H.; Wang, Z.; Marais, A.; Mystek, K.; Piper, A.; Granberg, H.; Malti, A.; Gatenholm, P.; Larsson, P. A.; Wågberg, L., Ambient‐dried, 3D‐printable and electrically conducting cellulose nanofiber aerogels by inclusion of functional polymers. Advanced Functional Materials 2020, 30 (12), 1909383. 97. Huang, X.; Wei, J.; Zhang, Y.; Qian, B.; Jia, Q.; Liu, J.; Zhao, X.; Shao, G., Ultralight magnetic and dielectric aerogels achieved by metal–organic framework initiated gelation of graphene oxide for enhanced microwave absorption. Nano-Micro Letters 2022, 14 (1), 107. 98. Li, C.; Cao, S.; Lutzki, J.; Yang, J.; Konegger, T.; Kleitz, F.; Thomas, A., A covalent organic framework/graphene dual-region hydrogel for enhanced solar-driven water generation. Journal of the American Chemical Society 2022, 144 (7), 3083-3090. 99. Fei, Y.; Liang, M.; Yan, L.; Chen, Y.; Zou, H., Co/C@cellulose nanofiber aerogel derived from metal-organic frameworks for highly efficient electromagnetic interference shielding. Chemical Engineering Journal 2020, 392, 124815. 100. Li, L.; Chen, R.; Li, Y.; Xiong, T.; Li, Y., Novel cotton fiber-covalent organic framework hybrid monolith for reversible capture of iodine. Cellulose 2020, 27, 5879-5892. 101. Li, Y.; Li, Y.; Zhao, Q.; Li, L.; Chen, R.; He, C., Cotton fiber functionalized with 2D covalent organic frameworks for iodine capture. Cellulose 2020, 27, 1517-1529. 102. Li, F.; Ding, L. G.; Yao, B. J.; Huang, N.; Li, J. T.; Fu, Q. J.; Dong, Y. B., Pd loaded and covalent-organic framework involved chitosan aerogels and their application for continuous flow-through aqueous CB decontamination. Journal of Materials Chemistry A 2018, 6 (24), 11140-11146. 103. Liu, K.; Yang, J.; Liu, J.; Shuai, Q.; Yamauchi, Y.; Han, M.; Huang, L., Robust self-floating covalent organic framework/chitosan aerogels for the efficient removal of sulfamerazine. Chemical Engineering Journal 2023, 472, 144966. 104. Huang, N.; Drake, H.; Li, J.; Pang, J.; Wang, Y.; Yuan, S.; Wang, Q.; Cai, P.; Qin, J.; Zhou, H. C., Flexible and hierarchical metal–organic framework composites for high‐performance catalysis. Angewandte Chemie International Edition 2018, 57 (29), 8916-8920. 234 105. Li, J.; Yang, Y.; Ma, W.; Li, G.; Lu, Q.; Lin, Z., One-pot room-temperature synthesis of covalent organic framework-coated superhydrophobic sponges for highly efficient oil-water separation. Journal of Hazardous Materials 2021, 411, 125190. 106. Ghaffarkhah, A.; Hashemi, S. A.; Isari, A. A.; Panahi-Sarmad, M.; Jiang, F.; Russell, T. P.; Rojas, O. J.; Arjmand, M., Chemistry, applications, and future prospects of structured liquids. Chemical Society Reviews 2024, 53, 9652-9717 107. Li, X.; Huang, Z.; Shuck, C. E.; Liang, G.; Gogotsi, Y.; Zhi, C., MXene chemistry, electrochemistry and energy storage applications. Nature Reviews Chemistry 2022, 6 (6), 389-404. 108. Lim, K. R. G.; Shekhirev, M.; Wyatt, B. C.; Anasori, B.; Gogotsi, Y.; Seh, Z. W., Fundamentals of MXene synthesis. Nature Synthesis 2022, 1 (8), 601-614. 109. Hashemi, S. A.; Ghaffarkhah, A.; Goodarzi, M.; Nazemi, A.; Banvillet, G.; Milani, A. S.; Soroush, M.; Rojas, O. J.; Ramakrishna, S.; Wuttke, S., Liquid‐templating aerogels. Advanced Materials 2023, 35 (42), 2302826. 110. Hashemi, S. A.; Ghaffarkhah, A.; Hosseini, E.; Bahrani, S.; Najmi, P.; Omidifar, N.; Mousavi, S. M.; Amini, M.; Ghaedi, M.; Ramakrishna, S., Recent progress on hybrid fibrous electromagnetic shields: key protectors of living species against electromagnetic radiation. Matter 2022, 5 (11), 3807-3868. 111. Ghaffarkhah, A.; Hashemi, S. A.; Ahmadijokani, F.; Goodarzi, M.; Riazi, H.; Mhatre, S. E.; Zaremba, O.; Rojas, O. J.; Soroush, M.; Russell, T. P., Functional Janus structured liquids and aerogels. Nature Communications 2023, 14 (1), 7811. 112. Marcano, D. C.; Kosynkin, D. V.; Berlin, J. M.; Sinitskii, A.; Sun, Z.; Slesarev, A.; Alemany, L. B.; Lu, W.; Tour, J. M., Improved synthesis of graphene oxide. ACS Nano 2010, 4 (8), 4806-4814. 113. Saito, T.; Kimura, S.; Nishiyama, Y.; Isogai, A., Cellulose nanofibers prepared by TEMPO-mediated oxidation of native cellulose. Biomacromolecules 2007, 8 (8), 2485-2491. 114. Biliuta, G.; Fras, L.; Drobota, M.; Persin, Z.; Kreze, T.; Stana-Kleinschek, K.; Ribitsch, V.; Harabagiu, V.; Coseri, S., Comparison study of TEMPO and phthalimide-N-oxyl (PINO) radicals on oxidation efficiency toward cellulose. Carbohydrate polymers 2013, 91 (2), 502-507. 115. Ossonon, B. D.; Bélanger, D., Synthesis and characterization of sulfophenyl-functionalized reduced graphene oxide sheets. RSC Advances 2017, 7 (44), 27224-27234. 116. Hashemi, S. A.; Bahrani, S.; Mousavi, S. M.; Omidifar, N.; Arjmand, M.; Lankarani, K. B.; Shokripour, M.; Ramakrishna, S., Differentiable detection of ethanol/methanol in biological fluids using prompt graphene-based electrochemical nanosensor coupled with catalytic complex of nickel oxide/8-hydroxyquinoline. Analytica Chimica Acta 2022, 1194, 339407. 117. Pimenta, M.; Dresselhaus, G.; Dresselhaus, M. S.; Cancado, L.; Jorio, A.; Saito, R., Studying disorder in graphite-based systems by Raman spectroscopy. Physical Chemistry Chemical Physics 2007, 9 (11), 1276-1290. 118. De Silva, K. K. H.; Viswanath, P.; Rao, V. K.; Suzuki, S.; Yoshimura, M., New insight into the characterization of graphene oxide and reduced graphene oxide monolayer flakes on Si-based substrates by optical microscopy and Raman spectroscopy. The Journal of Physical Chemistry C 2021, 125 (14), 7791-7798. 235 119. Hashemi, S. A.; Bahrani, S.; Mousavi, S. M.; Omidifar, N.; Behbahan, N. G. G.; Arjmand, M.; Ramakrishna, S.; Dimiev, A. M.; Lankarani, K. B.; Moghadami, M., Antibody mounting capability of 1D/2D carbonaceous nanomaterials toward rapid-specific detection of SARS-CoV-2. Talanta 2022, 239, 123113. 120. Hashemi, S. A.; Naderi, H. R.; Mousavi, S. M.; Bahrani, S.; Arjmand, M.; Dimiev, A. M.; Ramakrishna, S., Synergic effect of laser-assisted graphene with silver nanowire reinforced polyindole/polypyrrole toward superior energy density. Carbon 2022, 188, 276-288. 121. Covarrubias-García, I.; Quijano, G.; Aizpuru, A.; Sánchez-García, J. L.; Rodríguez-López, J. L.; Arriaga, S., Reduced graphene oxide decorated with magnetite nanoparticles enhance biomethane enrichment. Journal of Hazardous Materials 2020, 397, 122760. 122. Hashemi, S. A.; Mousavi, S. M.; Naderi, H. R.; Bahrani, S.; Arjmand, M.; Hagfeldt, A.; Chiang, W. H.; Ramakrishna, S., Reinforced polypyrrole with 2D graphene flakes decorated with interconnected nickel-tungsten metal oxide complex toward superiorly stable supercapacitor. Chemical Engineering Journal 2021, 418, 129396. 123. Kiliyankil, V. A.; Fugetsu, B.; Sakata, I.; Wang, Z.; Endo, M., Aerogels from copper (II)-cellulose nanofibers and carbon nanotubes as absorbents for the elimination of toxic gases from air. Journal of Colloid and Interface Science 2021, 582, 950-960. 124. Poyraz, B.; Tozluoğlu, A.; Candan, Z.; Demir, A.; Yavuz, M.; Büyuksarı, Ü.; Ünal, H. İ.; Fidan, H.; Saka, R. C., TEMPO-treated CNF composites: pulp and matrix effect. Fibers and Polymers 2018, 19 (1), 195-204. 125. Abd El-Aziz, M. E.; Morsi, S. M.; Salama, D. M.; Abd Elwahed, M. S.; Shaaban, E. A.; Abou-Zeid, R. E., Modification of TEMPO-oxidized cellulose nanofibers as a source of potassium and its impact on onion plant. Carbohydrate Polymer Technologies and Applications 2023, 6, 100388. 126. Forth, J.; Kim, P. Y.; Xie, G.; Liu, X.; Helms, B. A.; Russell, T. P., Building reconfigurable devices using complex liquid–fluid interfaces. Advanced Materials 2019, 31 (18), 1806370. 127. Tardy, B. L.; Mattos, B. D.; Otoni, C. G.; Beaumont, M.; Majoinen, J.; Kämäräinen, T.; Rojas, O. J., Deconstruction and reassembly of renewable polymers and biocolloids into next generation structured materials. Chemical Reviews 2021, 121 (22), 14088-14188. 128. Sun, H.; Li, M.; Li, L.; Liu, T.; Luo, Y.; Russell, T. P.; Shi, S., Redox-responsive, reconfigurable all-liquid constructs. Journal of the American Chemical Society 2021, 143 (10), 3719-3722. 129. Sun, H.; Li, L.; Russell, T. P.; Shi, S., Photoresponsive structured liquids enabled by molecular recognition at liquid–liquid interfaces. Journal of the American Chemical Society 2020, 142 (19), 8591-8595. 130. Sun, S.; Xie, C.; Chen, J.; Yang, Y.; Li, H.; Russell, T. P.; Shi, S., Responsive Interfacial Assemblies Based on Charge‐Transfer Interactions. Angewandte Chemie 2021, 133 (50), 26567-26571. 131. Grande, R.; Bai, L.; Wang, L.; Xiang, W.; Ikkala, O.; Carvalho, A. J.; Rojas, O. J., Nanochitins of varying aspect ratio and properties of microfibers produced by interfacial 236 complexation with seaweed alginate. ACS Sustainable Chemistry & Engineering 2019, 8 (2), 1137-1145. 132. Gu, P. Y.; Zhou, F.; Xie, G.; Kim, P. Y.; Chai, Y.; Hu, Q.; Shi, S.; Xu, Q. F.; Liu, F.; Lu, J. M., Visualizing interfacial jamming using an aggregation‐induced‐emission molecular reporter. Angewandte Chemie International Edition 2021, 60 (16), 8694-8699. 133. Xie, G.; Forth, J.; Chai, Y.; Ashby, P. D.; Helms, B. A.; Russell, T. P., Compartmentalized, all-aqueous flow-through-coordinated reaction systems. Chem 2019, 5 (10), 2678-2690. 134. Hua, X.; Bevan, M. A.; Frechette, J., Competitive adsorption between nanoparticles and surface active ions for the oil–water interface. Langmuir 2018, 34 (16), 4830-4842. 135. Liu, X.; Kent, N.; Ceballos, A.; Streubel, R.; Jiang, Y.; Chai, Y.; Kim, P. Y.; Forth, J.; Hellman, F.; Shi, S., Reconfigurable ferromagnetic liquid droplets. Science 2019, 365 (6450), 264-267. 136. Li, L.; Sun, H.; Li, M.; Yang, Y.; Russell, T. P.; Shi, S., Gated molecular diffusion at liquid–liquid interfaces. Angewandte Chemie International Edition 2021, 60 (32), 17394-17397. 137. Chai, Y.; Hasnain, J.; Bahl, K.; Wong, M.; Li, D.; Geissler, P.; Kim, P. Y.; Jiang, Y.; Gu, P.; Li, S., Direct observation of nanoparticle-surfactant assembly and jamming at the water-oil interface. Science Advances 2020, 6 (48), eabb8675. 138. Kim, F.; Cote, L. J.; Huang, J., Graphene oxide: surface activity and two‐dimensional assembly. Advanced Materials 2010, 22 (17), 1954-1958. 139. Huang, Y.; Gong, S. D.; Huang, R.; Cao, H. J.; Lin, Y. H.; Yang, M.; Li, X., Polyhedral oligomeric silsesquioxane containing gel polymer electrolyte based on a PMMA matrix. RSC Advances 2015, 5 (57), 45908-45918. 140. Nie, W. Y.; Li, G.; Li, Y.; Xu, H. Y., Preparation and properties of a POSS-containing organic–inorganic hybrid crosslinked polymer. Chinese Chemical Letters 2009, 20 (6), 738-742. 141. Zhang, P.; Qin, B.; Xia, J., UV curable robust durable hydrophobic coating based on epoxy polyhedral oligomeric silsesquioxanes (EP-POSS) and their derivatives. ACS Omega 2022. 142. Prem Kumar, B.; Vijaykumar, B.; Raghavan, C.; Harshavardhan, S.; Yi, S. S.; Gandhi, S.; Jiang, J.; Jang, K.; Shin, D. S., POSS-based luminescent hybrid material for enhanced photo-emitting properties. Journal of Materials Science 2013, 48, 7533-7539. 143. Wang, B.; Shi, M.; Ding, J.; Huang, Z., Polyhedral oligomeric silsesquioxane (POSS)-modified phenolic resin: synthesis and anti-oxidation properties. e-Polymers 2021, 21 (1), 316-326. 144. Li, C. B.; Li, Y. J.; Zhao, Q.; Luo, Y.; Yang, G. Y.; Hu, Y.; Jiang, J. J., Electromagnetic interference shielding of graphene aerogel with layered microstructure fabricated via mechanical compression. ACS Applied Materials & Interfaces 2020, 12 (27), 30686-30694. 145. Song, W. L.; Guan, X. T.; Fan, L. Z.; Cao, W. Q.; Wang, C. Y.; Cao, M. S., Tuning three-dimensional textures with graphene aerogels for ultra-light flexible graphene/texture composites of effective electromagnetic shielding. Carbon 2015, 93, 151-160. 146. Zhang, Q.; Xu, X.; Li, H.; Xiong, G.; Hu, H.; Fisher, T. S., Mechanically robust honeycomb graphene aerogel multifunctional polymer composites. Carbon 2015, 93, 659-670. 237 147. Xu, X.; Li, H.; Zhang, Q.; Hu, H.; Zhao, Z.; Li, J.; Li, J.; Qiao, Y.; Gogotsi, Y., Self-sensing, ultralight, and conductive 3D graphene/iron oxide aerogel elastomer deformable in a magnetic field. ACS Nano 2015, 9 (4), 3969-3977. 148. Pang, K.; Song, X.; Xu, Z.; Liu, X.; Liu, Y.; Zhong, L.; Peng, Y.; Wang, J.; Zhou, J.; Meng, F., Hydroplastic foaming of graphene aerogels and artificially intelligent tactile sensors. Science Advances 2020, 6 (46), eabd4045. 149. Hu, H.; Zhao, Z.; Wan, W.; Gogotsi, Y.; Qiu, J., Ultralight and highly compressible graphene aerogels. Advanced Materials 2013, 25 (15), 2219-2223. 150. Sun, H.; Xu, Z.; Gao, C., Multifunctional, ultra‐flyweight, synergistically assembled carbon aerogels. Advanced Materials 2013, 25 (18), 2554-2560. 151. Wang, M.; Anoshkin, I. V.; Nasibulin, A. G.; Korhonen, J. T.; Seitsonen, J.; Pere, J.; Kauppinen, E. I.; Ras, R. H.; Ikkala, O., Modifying native nanocellulose aerogels with carbon nanotubes for mechanoresponsive conductivity and pressure sensing. Advanced Materials 2013, 25 (17), 2428-2432. 152. Wang, Z.; Dai, Z.; Wu, J.; Zhao, N.; Xu, J., Vacuum‐dried robust bridged silsesquioxane aerogels. Advanced Materials 2013, 25 (32), 4494-4497. 153. Peng, Q.; Li, Y.; He, X.; Gui, X.; Shang, Y.; Wang, C.; Wang, C.; Zhao, W.; Du, S.; Shi, E., Graphene nanoribbon aerogels unzipped from carbon nanotube sponges. Advanced Materials 2014, 26 (20), 3241-3247. 154. Yang, X.; Shi, K.; Zhitomirsky, I.; Cranston, E. D., Cellulose nanocrystal aerogels as universal 3D lightweight substrates for supercapacitor materials. Advanced Materials 2015, 27 (40), 6104-6109. 155. Lin, Y.; Liu, F.; Casano, G.; Bhavsar, R.; Kinloch, I. A.; Derby, B., Pristine graphene aerogels by room‐temperature freeze gelation. Advanced Materials 2016, 28 (36), 7993-8000. 156. Si, Y.; Wang, X.; Yan, C.; Yang, L.; Yu, J.; Ding, B., Ultralight biomass‐derived carbonaceous nanofibrous aerogels with superelasticity and high pressure‐sensitivity. Advanced Materials 2016, 28 (43), 9512-9518. 157. Xu, X.; Zhang, Q.; Yu, Y.; Chen, W.; Hu, H.; Li, H., Naturally dried graphene aerogels with superelasticity and tunable Poisson's ratio. Advanced Materials 2016, 28 (41), 9223-9230. 158. Zhao, X.; Yao, W.; Gao, W.; Chen, H.; Gao, C., Wet‐Spun superelastic graphene aerogel millispheres with group effect. Advanced Materials 2017, 29 (35), 1701482. 159. Yu, Z. L.; Qin, B.; Ma, Z. Y.; Huang, J.; Li, S. C.; Zhao, H. Y.; Li, H.; Zhu, Y. B.; Wu, H. A.; Yu, S. H., Superelastic hard carbon nanofiber aerogels. Advanced Materials 2019, 31 (23), 1900651. 160. Dong, X.; Cao, L.; Si, Y.; Ding, B.; Deng, H., Cellular structured CNTs@SiO2 nanofibrous aerogels with vertically aligned vessels for salt‐resistant solar desalination. Advanced Materials 2020, 32 (34), 1908269. 161. Tetik, H.; Orangi, J.; Yang, G.; Zhao, K.; Mujib, S. B.; Singh, G.; Beidaghi, M.; Lin, D., 3D printed MXene aerogels with truly 3D macrostructure and highly engineered microstructure 238 for enhanced electrical and electrochemical performance. Advanced Materials 2022, 34 (2), 2104980. 162. Zhong, L.; Chen, X.; Song, H.; Guo, K.; Hu, Z., Highly flexible silica aerogels derived from methyltriethoxysilane and polydimethylsiloxane. New Journal of Chemistry 2015, 39 (10), 7832-7838. 163. Wei, Y.; Wang, J.; Zhang, Y.; Wang, L.; Zhang, X., Autocatalytic synthesis of molecular-bridged silica aerogels with excellent absorption and super elasticity. RSC Advances 2015, 5 (111), 91407-91413. 164. Shu, J. C.; Cao, W. Q.; Cao, M. S., Diverse metal–organic framework architectures for electromagnetic absorbers and shielding. Advanced Functional Materials 2021, 31 (23), 2100470. 165. Bi, S.; Zhang, L.; Mu, C.; Lee, H. Y.; Cheah, J. W.; Chua, E. K.; See, K. Y.; Liu, M.; Hu, X., A comparative study on electromagnetic interference shielding behaviors of chemically reduced and thermally reduced graphene aerogels. Journal of Colloid and Interface Science 2017, 492, 112-118. 166. Han, D.; Zhao, Y. H.; Bai, S. L.; Ping, W. C., High shielding effectiveness of multilayer graphene oxide aerogel film/polymer composites. RSC Advances 2016, 6 (95), 92168-92174. 167. Xi, J.; Li, Y.; Zhou, E.; Liu, Y.; Gao, W.; Guo, Y.; Ying, J.; Chen, Z.; Chen, G.; Gao, C., Graphene aerogel films with expansion enhancement effect of high-performance electromagnetic interference shielding. Carbon 2018, 135, 44-51. 168. Chen, Y.; Zhang, H. B.; Wang, M.; Qian, X.; Dasari, A.; Yu, Z. Z., Phenolic resin-enhanced three-dimensional graphene aerogels and their epoxy nanocomposites with high mechanical and electromagnetic interference shielding performances. Composites Science and Technology 2017, 152, 254-262. 169. Bi, S.; Zhang, L.; Mu, C.; Liu, M.; Hu, X., Electromagnetic interference shielding properties and mechanisms of chemically reduced graphene aerogels. Applied Surface Science 2017, 412, 529-536. 170. Guo, T.; Chen, X.; Su, L.; Li, C.; Huang, X.; Tang, X. Z., Stretched graphene nanosheets formed the “obstacle walls” in melamine sponge towards effective electromagnetic interference shielding applications. Materials & Design 2019, 182, 108029. 171. Gao, W.; Zhao, N.; Yu, T.; Xi, J.; Mao, A.; Yuan, M.; Bai, H.; Gao, C., High-efficiency electromagnetic interference shielding realized in nacre-mimetic graphene/polymer composite with extremely low graphene loading. Carbon 2020, 157, 570-577. 172. Fan, Z.; Wang, D.; Yuan, Y.; Wang, Y.; Cheng, Z.; Liu, Y.; Xie, Z., A lightweight and conductive MXene/graphene hybrid foam for superior electromagnetic interference shielding. Chemical Engineering Journal 2020, 381, 122696. 173. Zhao, S.; Zhang, H. B.; Luo, J. Q.; Wang, Q. W.; Xu, B.; Hong, S.; Yu, Z. Z., Highly electrically conductive three-dimensional Ti3C2Tx MXene/reduced graphene oxide hybrid aerogels with excellent electromagnetic interference shielding performances. ACS Nano 2018, 12 (11), 11193-11202. 239 174. Bian, R.; He, G.; Zhi, W.; Xiang, S.; Wang, T.; Cai, D., Ultralight MXene-based aerogels with high electromagnetic interference shielding performance. Journal of Materials Chemistry C 2019, 7 (3), 474-478. 175. Liu, J.; Zhang, H. B.; Sun, R.; Liu, Y.; Liu, Z.; Zhou, A.; Yu, Z. Z., Hydrophobic, flexible, and lightweight MXene foams for high‐performance electromagnetic‐interference shielding. Advanced Materials 2017, 29 (38), 1702367. 176. Zhou, Z.; Liu, J.; Zhang, X.; Tian, D.; Zhan, Z.; Lu, C., Ultrathin MXene/calcium alginate aerogel film for high‐performance electromagnetic interference shielding. Advanced Materials Interfaces 2019, 6 (6), 1802040. 177. Liang, C.; Qiu, H.; Song, P.; Shi, X.; Kong, J.; Gu, J., Ultra-light MXene aerogel/wood-derived porous carbon composites with wall-like “mortar/brick” structures for electromagnetic interference shielding. Science Bulletin 2020, 65 (8), 616-622. 178. Weng, C.; Wang, G.; Dai, Z.; Pei, Y.; Liu, L.; Zhang, Z., Buckled AgNW/MXene hybrid hierarchical sponges for high-performance electromagnetic interference shielding. Nanoscale 2019, 11 (47), 22804-22812. 179. Sambyal, P.; Iqbal, A.; Hong, J.; Kim, H.; Kim, M. K.; Hong, S. M.; Han, M.; Gogotsi, Y.; Koo, C. M., Ultralight and mechanically robust Ti3C2Tx hybrid aerogel reinforced by carbon nanotubes for electromagnetic interference shielding. ACS Applied Materials & Interfaces 2019, 11 (41), 38046-38054. 180. Wu, X.; Han, B.; Zhang, H. B.; Xie, X.; Tu, T.; Zhang, Y.; Dai, Y.; Yang, R.; Yu, Z.-Z., Compressible, durable and conductive polydimethylsiloxane-coated MXene foams for high-performance electromagnetic interference shielding. Chemical Engineering Journal 2020, 381, 122622. 181. Huang, H. D.; Liu, C. Y.; Zhou, D.; Jiang, X.; Zhong, G. J.; Yan, D. X.; Li, Z. M., Cellulose composite aerogel for highly efficient electromagnetic interference shielding. Journal of Materials Chemistry A 2015, 3 (9), 4983-4991. 182. Zhou, Z. H.; Li, M. Z.; Huang, H. D.; Li, L.; Yang, B.; Yan, D. X.; Li, Z. M., Structuring hierarchically porous architecture in biomass-derived carbon aerogels for simultaneously achieving high electromagnetic interference shielding effectiveness and high absorption coefficient. ACS Applied Materials & Interfaces 2020, 12 (16), 18840-18849. 183. Hu, P.; Lyu, J.; Fu, C.; Gong, W. B.; Liao, J.; Lu, W.; Chen, Y.; Zhang, X., Multifunctional aramid nanofiber/carbon nanotube hybrid aerogel films. ACS Nano 2019, 14 (1), 688-697. 184. Kumar, R.; Mondal, D.; Chaudhary, A.; Shafeeq, M.; Kumari, S., Excellent EMI shielding performance and thermal insulating properties in lightweight, multifunctional carbon-cenosphere composite foams. Composites Part A: Applied Science and Manufacturing 2018, 112, 475-484. 185. Farhan, S.; Wang, R.; Li, K., Electromagnetic interference shielding effectiveness of carbon foam containing in situ grown silicon carbide nanowires. Ceramics International 2016, 42 (9), 11330-11340. 240 186. Ameli, A.; Nofar, M.; Wang, S.; Park, C. B., Lightweight polypropylene/stainless-steel fiber composite foams with low percolation for efficient electromagnetic interference shielding. ACS applied materials & interfaces 2014, 6 (14), 11091-11100. 187. Zhang, L.; Liu, M.; Roy, S.; Chu, E. K.; See, K. Y.; Hu, X., Phthalonitrile-based carbon foam with high specific mechanical strength and superior electromagnetic interference shielding performance. ACS applied materials & interfaces 2016, 8 (11), 7422-7430. 188. Zhang, J.; Kong, N.; Uzun, S.; Levitt, A.; Seyedin, S.; Lynch, P. A.; Qin, S.; Han, M.; Yang, W.; Liu, J., Scalable Manufacturing of Free‐Standing, Strong Ti3C2Tx MXene Films with Outstanding Conductivity. Advanced Materials 2020, 2001093. 189. Zeng, J.; Ji, X.; Ma, Y.; Zhang, Z.; Wang, S.; Ren, Z.; Zhi, C.; Yu, J., 3D graphene fibers grown by thermal chemical vapor deposition. Advanced Materials 2018, 30 (12), 1705380. 190. Shen, B.; Zhai, W.; Zheng, W., Ultrathin flexible graphene film: an excellent thermal conducting material with efficient EMI shielding. Advanced Functional Materials 2014, 24 (28), 4542-4548. 191. Sun, R.; Zhang, H. B.; Liu, J.; Xie, X.; Yang, R.; Li, Y.; Hong, S.; Yu, Z. Z., Highly conductive transition metal carbide/carbonitride (MXene)@polystyrene nanocomposites fabricated by electrostatic assembly for highly efficient electromagnetic interference shielding. Advanced Functional Materials 2017, 27 (45), 1702807. 192. Li, Y.; Tian, X.; Gao, S. P.; Jing, L.; Li, K.; Yang, H.; Fu, F.; Lee, J. Y.; Guo, Y. X.; Ho, J. S., Reversible crumpling of 2D titanium carbide (MXene) nanocoatings for stretchable electromagnetic shielding and wearable wireless communication. Advanced Functional Materials 2020, 30 (5), 1907451. 193. Song, Q.; Ye, F.; Yin, X.; Li, W.; Li, H.; Liu, Y.; Li, K.; Xie, K.; Li, X.; Fu, Q., Carbon nanotube–multilayered graphene edge plane core–shell hybrid foams for ultrahigh‐performance electromagnetic‐interference shielding. Advanced Materials 2017, 29 (31), 1701583. 194. Zeng, Z.; Jin, H.; Chen, M.; Li, W.; Zhou, L.; Zhang, Z., Lightweight and anisotropic porous MWCNT/WPU composites for ultrahigh performance electromagnetic interference shielding. Advanced Functional Materials 2016, 26 (2), 303-310. 195. Tan, M.; Chen, D.; Cheng, Y.; Sun, H.; Chen, G.; Dong, S.; Zhao, G.; Sun, B.; Wu, S.; Zhang, W., Anisotropically Oriented Carbon Films with Dual‐Function of Efficient Heat Dissipation and Excellent Electromagnetic Interference Shielding Performances. Advanced Functional Materials 2022, 2202057. 196. Chen, Y.; Zhang, H. B.; Yang, Y.; Wang, M.; Cao, A.; Yu, Z. Z., High‐performance epoxy nanocomposites reinforced with three‐dimensional carbon nanotube sponge for electromagnetic interference shielding. Advanced Functional Materials 2016, 26 (3), 447-455. 197. Zhou, Q.; Lyu, J.; Wang, G.; Robertson, M.; Qiang, Z.; Sun, B.; Ye, C.; Zhu, M., Mechanically strong and multifunctional hybrid hydrogels with ultrahigh electrical conductivity. Advanced Functional Materials 2021, 31 (40), 2104536. 198. Gong, S.; Sheng, X.; Li, X.; Sheng, M.; Wu, H.; Lu, X.; Qu, J., A Multifunctional flexible composite film with excellent multi‐source driven thermal management, electromagnetic 241 interference shielding, and fire safety performance, inspired by a “Brick–Mortar” sandwich structure. Advanced Functional Materials 2022, 2200570. 199. Ma, Z.; Xiang, X.; Shao, L.; Zhang, Y.; Gu, J., Multifunctional wearable silver nanowire decorated leather nanocomposites for joule heating, electromagnetic interference shielding and piezoresistive sensing. Angewandte Chemie International Edition 2022, 61 (15), e202200705. 200. Ying, M.; Zhao, R.; Hu, X.; Zhang, Z.; Liu, W.; Yu, J.; Liu, X.; Liu, X.; Rong, H.; Wu, C., Wrinkled titanium carbide (MXene) with surface charge polarizations through chemical etching for superior electromagnetic interference shielding. Angewandte Chemie 2022, 134 (16), e202201323. 201. Wang, L.; Qiu, H.; Liang, C.; Song, P.; Han, Y.; Han, Y.; Gu, J.; Kong, J.; Pan, D.; Guo, Z., Electromagnetic interference shielding MWCNT-Fe3O4@Ag/epoxy nanocomposites with satisfactory thermal conductivity and high thermal stability. Carbon 2019, 141, 506-514. 202. Chen, H.; Wen, Y.; Qi, Y.; Zhao, Q.; Qu, L.; Li, C., Pristine titanium carbide MXene films with environmentally stable conductivity and superior mechanical strength. Advanced Functional Materials 2020, 30 (5), 1906996. 203. Wan, Y. J.; Zhu, P. L.; Yu, S. H.; Sun, R.; Wong, C. P.; Liao, W. H., Anticorrosive, ultralight, and flexible carbon‐wrapped metallic nanowire hybrid sponges for highly efficient electromagnetic interference shielding. Small 2018, 14 (27), 1800534. 204. Zhang, K.; Li, G. H.; Feng, L. M.; Wang, N.; Guo, J.; Sun, K.; Yu, K. X.; Zeng, J. B.; Li, T.; Guo, Z., Ultralow percolation threshold and enhanced electromagnetic interference shielding in poly (L-lactide)/multi-walled carbon nanotube nanocomposites with electrically conductive segregated networks. Journal of Materials Chemistry C 2017, 5 (36), 9359-9369. 205. Gebrekrstos, A.; Biswas, S.; Menon, A. V.; Madras, G.; Pötschke, P.; Bose, S., Multi-layered stack consisting of PVDF nanocomposites with flow-induced oriented MWCNT structure can supress electromagnetic radiation. Composites Part B: Engineering 2019, 166, 749-757. 206. Kong, L.; Yin, X.; Xu, H.; Yuan, X.; Wang, T.; Xu, Z.; Huang, J.; Yang, R.; Fan, H., Powerful absorbing and lightweight electromagnetic shielding CNTs/RGO composite. Carbon 2019, 145, 61-66. 207. Shen, B.; Li, Y.; Yi, D.; Zhai, W.; Wei, X.; Zheng, W., Microcellular graphene foam for improved broadband electromagnetic interference shielding. Carbon 2016, 102, 154-160. 208. Jia, L. C.; Li, Y. K.; Yan, D. X., Flexible and efficient electromagnetic interference shielding materials from ground tire rubber. Carbon 2017, 121, 267-273. 209. Song, W. L.; Guan, X. T.; Fan, L. Z.; Cao, W. Q.; Wang, C. Y.; Zhao, Q. L.; Cao, M. S., Magnetic and conductive graphene papers toward thin layers of effective electromagnetic shielding. Journal of Materials Chemistry A 2015, 3 (5), 2097-2107. 210. Xu, H.; Yin, X.; Li, X.; Li, M.; Liang, S.; Zhang, L.; Cheng, L., Lightweight Ti2CTx MXene/poly (vinyl alcohol) composite foams for electromagnetic wave shielding with absorption-dominated feature. ACS Applied Materials & Interfaces 2019, 11 (10), 10198-10207. 211. Zhou, B.; Zhang, Z.; Li, Y.; Han, G.; Feng, Y.; Wang, B.; Zhang, D.; Ma, J.; Liu, C., Flexible, robust, and multifunctional electromagnetic interference shielding film with alternating 242 cellulose nanofiber and MXene layers. ACS Applied Materials & Interfaces 2020, 12 (4), 4895-4905. 212. Zhang, H.; Zhang, G.; Tang, M.; Zhou, L.; Li, J.; Fan, X.; Shi, X.; Qin, J., Synergistic effect of carbon nanotube and graphene nanoplates on the mechanical, electrical and electromagnetic interference shielding properties of polymer composites and polymer composite foams. Chemical Engineering Journal 2018, 353, 381-393. 213. Sheng, A.; Ren, W.; Yang, Y.; Yan, D. X.; Duan, H.; Zhao, G.; Liu, Y.; Li, Z. M., Multilayer WPU conductive composites with controllable electro-magnetic gradient for absorption-dominated electromagnetic interference shielding. Composites Part A: Applied Science and Manufacturing 2020, 129, 105692. 214. Yang, G. Y.; Wang, S. Z.; Sun, H. T.; Yao, X. M.; Li, C. B.; Li, Y. J.; Jiang, J. J., Ultralight, Conductive Ti3C2Tx MXene/PEDOT: PSS Hybrid Aerogels for Electromagnetic Interference Shielding Dominated by the Absorption Mechanism. ACS Applied Materials & Interfaces 2021, 13 (48), 57521-57531. 215. Jin, X.; Wang, J.; Dai, L.; Liu, X.; Li, L.; Yang, Y.; Cao, Y.; Wang, W.; Wu, H.; Guo, S., Flame-retardant poly (vinyl alcohol)/MXene multilayered films with outstanding electromagnetic interference shielding and thermal conductive performances. Chemical Engineering Journal 2020, 380, 122475. 216. Sharif, F.; Arjmand, M.; Moud, A. A.; Sundararaj, U.; Roberts, E. P., Segregated hybrid poly (methyl methacrylate)/graphene/magnetite nanocomposites for electromagnetic interference shielding. ACS Applied Materials & Interfaces 2017, 9 (16), 14171-14179. 217. Lu, J.; Cheng, L.; Liao, C.; Jia, P.; Song, L.; Wang, B.; Hu, Y., Ultrathin and mechanically robust mussel byssus‐inspired MXene@aramid nanofibers materials with superior endurance in harsh environments for tunable EMI shielding performance. Advanced Materials Interfaces 2022, 2101359. 218. Xie, Y.; Liu, S.; Huang, K.; Chen, B.; Shi, P.; Chen, Z.; Liu, B.; Liu, K.; Wu, Z.; Chen, K., Ultra‐broadband strong electromagnetic interference shielding with ferromagnetic graphene quartz fabric. Advanced Materials 2022, 2202982. 219. Yin, G.; Wang, Y.; Wang, W.; Yu, D., Multilayer structured PANI/MXene/CF fabric for electromagnetic interference shielding constructed by layer-by-layer strategy. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2020, 601, 125047. 220. Wei, Q.; Pei, S.; Qian, X.; Liu, H.; Liu, Z.; Zhang, W.; Zhou, T.; Zhang, Z.; Zhang, X.; Cheng, H. M., Superhigh electromagnetic interference shielding of ultrathin aligned pristine graphene nanosheets film. Advanced Materials 2020, 32 (14), 1907411. 221. Habibpour, S.; Zarshenas, K.; Zhang, M.; Hamidinejad, M.; Ma, L.; Park, C. B.; Yu, A., Greatly enhanced electromagnetic interference shielding effectiveness and mechanical properties of polyaniline-frafted Ti3C2Tx MXene–PVDF composites. ACS Applied Materials & Interfaces 2022. 222. Liu, J.; Mckeon, L.; Garcia, J.; Pinilla, S.; Barwich, S.; Möbius, M.; Stamenov, P.; Coleman, J. N.; Nicolosi, V., Additive manufacturing of Ti3C2‐MXene‐functionalized conductive polymer hydrogels for electromagnetic‐interference shielding. Advanced Materials 2022, 34 (5), 2106253. 243 223. Zeng, Z.; Jiang, F.; Yue, Y.; Han, D.; Lin, L.; Zhao, S.; Zhao, Y. B.; Pan, Z.; Li, C.; Nyström, G., Flexible and ultrathin waterproof cellular membranes based on high‐conjunction metal‐wrapped polymer nanofibers for electromagnetic interference shielding. Advanced Materials 2020, 32 (19), 1908496. 224. Wang, J.; Li, Q.; Li, K.; Sun, X.; Wang, Y.; Zhuang, T.; Yan, J.; Wang, H., Ultra-high electrical conductivity in filler-free polymeric hydrogels toward thermoelectrics and electromagnetic interference shielding. Advanced Materials (Deerfield Beach, Fla.) 2022, 34 (12), e2109904. 225. Huang, X.; Huang, J.; Zhou, G.; Wei, Y.; Wu, P.; Dong, A.; Yang, D., Gelation‐assisted assembly of large‐area, highly aligned, and environmentally stable MXene films with an excellent trade‐off between mechanical and electrical properties. Small 2022, 2200829. 226. Xu, J.; Li, R.; Ji, S.; Zhao, B.; Cui, T.; Tan, X.; Gou, G.; Jian, J.; Xu, H.; Qiao, Y., Multifunctional graphene microstructures inspired by honeycomb for ultrahigh performance electromagnetic interference shielding and wearable applications. ACS Nano 2021, 15 (5), 8907-8918. 227. Huang, M.; Wang, L.; Li, X.; Wu, Z.; Zhao, B.; Pei, K.; Liu, X.; Zhang, X.; Che, R., Magnetic interacted interaction effect in MXene skeleton: enhanced thermal‐generation for electromagnetic interference shielding. Small 2022, 2201587. 228. Wu, H.; Xie, Y.; Ma, Y.; Zhang, B.; Xia, B.; Zhang, P.; Qian, W.; He, D.; Zhang, X.; Li, B. W., Aqueous MXene/Xanthan gum hybrid inks for screen‐printing electromagnetic shielding, Joule heater, and piezoresistive sensor. Small 2022, 18 (16), 2107087. 229. Han, M.; Shuck, C. E.; Rakhmanov, R.; Parchment, D.; Anasori, B.; Koo, C. M.; Friedman, G.; Gogotsi, Y., Beyond Ti3C2Tx: MXenes for electromagnetic interference shielding. ACS Nano 2020, 14 (4), 5008-5016. 230. Zeng, Z.; Jin, H.; Chen, M.; Li, W.; Zhou, L.; Xue, X.; Zhang, Z., Microstructure design of lightweight, flexible, and high electromagnetic shielding porous multiwalled carbon nanotube/polymer composites. Small 2017, 13 (34), 1701388. 231. Choi, H. K.; Lee, A.; Park, M.; Lee, D. S.; Bae, S.; Lee, S. K.; Lee, S. H.; Lee, T.; Kim, T. W., Hierarchical porous film with layer-by-layer assembly of 2D copper nanosheets for ultimate electromagnetic interference shielding. ACS Nano 2021, 15 (1), 829-839. 232. Tan, X.; Liu, T. H.; Zhou, W.; Yuan, Q.; Ying, J.; Yan, Q.; Lv, L.; Chen, L.; Wang, X.; Du, S., Enhanced electromagnetic shielding and thermal conductive properties of polyolefin composites with a Ti3C2Tx MXene/graphene framework connected by a hydrogen-bonded interface. ACS Nano 2022. 233. Wu, S.; Zou, M.; Li, Z.; Chen, D.; Zhang, H.; Yuan, Y.; Pei, Y.; Cao, A., Robust and stable Cu nanowire@ graphene core–shell aerogels for ultraeffective electromagnetic interference shielding. Small 2018, 14 (23), 1800634. 234. Lee, G. S.; Yun, T.; Kim, H.; Kim, I. H.; Choi, J.; Lee, S. H.; Lee, H. J.; Hwang, H. S.; Kim, J. G.; Kim, D. W., Mussel inspired highly aligned Ti3C2Tx MXene film with synergistic enhancement of mechanical strength and ambient stability. ACS Nano 2020, 14 (9), 11722-11732. 244 235. Zhou, T.; Xu, C.; Liu, H.; Wei, Q.; Wang, H.; Zhang, J.; Zhao, T.; Liu, Z.; Zhang, X.; Zeng, Y., Second time-scale synthesis of high-quality graphite films by quenching for effective electromagnetic interference shielding. ACS Nano 2020, 14 (3), 3121-3128. 236. Fu, C.; Sheng, Z.; Zhang, X., Laminated structural engineering strategy toward carbon nanotube-based aerogel films. ACS Nano 2022. 237. Cao, W. T.; Chen, F. F.; Zhu, Y. J.; Zhang, Y. G.; Jiang, Y. Y.; Ma, M. G.; Chen, F., Binary strengthening and toughening of MXene/cellulose nanofiber composite paper with nacre-inspired structure and superior electromagnetic interference shielding properties. ACS Nano 2018, 12 (5), 4583-4593. 238. Li, Y.; Liu, J.; Wang, E.; Shen, B.; Chen, J.; Zhang, M.; Zhang, F.; Zhao, J.; Zheng, W., Controllable growth of NiCo compounds with different morphologies and structures on carbon fabrics as EMI shields with improved absorptivity. Carbon 2022, 197, 508-518. 239. Wan, Y. J.; Wang, X. Y.; Li, X. M.; Liao, S. Y.; Lin, Z. Q.; Hu, Y. G.; Zhao, T.; Zeng, X. L.; Li, C. H.; Yu, S. H., Ultrathin densified carbon nanotube film with “metal-like” conductivity, superior mechanical strength, and ultrahigh electromagnetic interference shielding effectiveness. ACS Nano 2020, 14 (10), 14134-14145. 240. Yang, Y.; Chen, S.; Li, W.; Li, P.; Ma, J.; Li, B.; Zhao, X.; Ju, Z.; Chang, H.; Xiao, L., Reduced graphene oxide conformally wrapped silver nanowire networks for flexible transparent heating and electromagnetic interference shielding. ACS Nano 2020, 14 (7), 8754-8765. 241. Wu, Z.; Dong, J.; Li, X.; Zhao, X.; Ji, C.; Zhang, Q., Interlayer decoration of expanded graphite by polyimide resins for preparing highly thermally conductive composites with superior electromagnetic shielding performance. Carbon 2022, 198, 1-10. 242. Zhao, B.; Bai, P.; Yuan, M.; Yan, Z.; Fan, B.; Zhang, R.; Che, R., Recyclable magnetic carbon foams possessing voltage-controllable electromagnetic shielding and oil/water separation. Carbon 2022, 197, 570-578. 243. Wang, J.; Ma, X.; Zhou, J.; Du, F.; Teng, C., Bioinspired, high-strength, and flexible MXene/aramid fiber for electromagnetic interference shielding papers with Joule heating performance. ACS Nano 2022, 16 (4), 6700-6711. 244. He, X.; Feng, L.; Zhang, Z.; Hou, X.; Ye, X.; Song, Q.; Yang, Y.; Suo, G.; Zhang, L.; Fu, Q. G., High-performance multifunctional carbon–silicon carbide composites with strengthened reduced graphene oxide. ACS Nano 2021, 15 (2), 2880-2892. 245. Wang, K.; Chen, C.; Zheng, Q.; Xiong, J.; Liu, H.; Yang, L.; Chen, Y.; Li, H., Multifunctional recycled carbon fiber-Ti3C2Tx MXene paper with superior electromagnetic interference shielding and photo/electro-thermal conversion performances. Carbon 2022, 197, 87-97. 246. Peng, M.; Zhu, Y.; Li, H.; He, K.; Zeng, G.; Chen, A.; Huang, Z.; Huang, T.; Yuan, L.; Chen, G., Synthesis and application of modified commercial sponges for oil-water separation. Chemical Engineering Journal 2019, 373, 213-226. 247. Yue, X.; Li, Z.; Zhang, T.; Yang, D.; Qiu, F., Design and fabrication of superwetting fiber-based membranes for oil/water separation applications. Chemical Engineering Journal 2019, 364, 292-309. 245 248. Wang, J.; Zhang, W.; Zhang, C., Versatile fabrication of anisotropic and superhydrophobic aerogels for highly selective oil absorption. Carbon 2019, 155, 16-24. 249. Yi, L.; Yang, J.; Fang, X.; Xia, Y.; Zhao, L.; Wu, H.; Guo, S., Facile fabrication of wood-inspired aerogel from chitosan for efficient removal of oil from Water. Journal of Hazardous Materials 2020, 385, 121507. 250. Tian, N.; Wu, S.; Han, G.; Zhang, Y.; Li, Q.; Dong, T., Biomass-derived oriented neurovascular network-like superhydrophobic aerogel as robust and recyclable oil droplets captor for versatile oil/water separation. Journal of Hazardous Materials 2022, 424, 127393. 251. Chen, P.; Bai, D.; Tang, H.; Liu, H.; Wang, J.; Gao, G.; Li, L., Polylactide aerogel with excellent comprehensive performances imparted by stereocomplex crystallization for efficient oil-water separation. Polymer 2022, 255, 125128. 252. Li, N.; Yue, Q.; Gao, B.; Xu, X.; Su, R., One-step synthesis of peanut hull/graphene aerogel for highly efficient oil-water separation. Journal of Cleaner Production 2019, 207, 764-771. 253. Yin, Z.; Sun, X.; Bao, M.; Li, Y., Construction of a hydrophobic magnetic aerogel based on chitosan for oil/water separation applications. International Journal of Biological Macromolecules 2020, 165, 1869-1880. 254. Zhai, T.; Zheng, Q.; Cai, Z.; Xia, H.; Gong, S., Synthesis of polyvinyl alcohol/cellulose nanofibril hybrid aerogel microspheres and their use as oil/solvent superabsorbents. Carbohydrate Polymers 2016, 148, 300-308. 255. Li, Z.; Shao, L.; Hu, W.; Zheng, T.; Lu, L.; Cao, Y.; Chen, Y., Excellent reusable chitosan/cellulose aerogel as an oil and organic solvent absorbent. Carbohydrate Polymers 2018, 191, 183-190. 256. Chhajed, M.; Yadav, C.; Agrawal, A. K.; Maji, P. K., Esterified superhydrophobic nanofibrillated cellulose based aerogel for oil spill treatment. Carbohydrate Polymers 2019, 226, 115286. 257. Zhang, M.; Jiang, S.; Han, F.; Li, M.; Wang, N.; Liu, L., Anisotropic cellulose nanofiber/chitosan aerogel with thermal management and oil absorption properties. Carbohydrate Polymers 2021, 264, 118033. 258. Lin, Y. Z.; Zhong, L. B.; Dou, S.; Shao, Z. D.; Liu, Q.; Zheng, Y. M., Facile synthesis of electrospun carbon nanofiber/graphene oxide composite aerogels for high efficiency oils absorption. Environment International 2019, 128, 37-45. 259. Cao, J.; Wang, Z.; Yang, X.; Tu, J.; Wu, R.; Wang, W., Green synthesis of amphipathic graphene aerogel constructed by using the framework of polymer-surfactant complex for water remediation. Applied Surface Science 2018, 444, 399-406. 260. Zhang, D.; Lin, Y.; Wang, W.; Li, Y.; Wu, G., Mechanically strong polyimide aerogels cross-linked with dopamine-functionalized carbon nanotubes for oil absorption. Applied Surface Science 2021, 543, 148833. 261. Lei, E.; Li, W.; Ma, C.; Liu, S., An ultra-lightweight recyclable carbon aerogel from bleached softwood kraft pulp for efficient oil and organic absorption. Materials Chemistry and Physics 2018, 214, 291-296. 246 262. Le, D. K.; Ng, G. N.; Koh, H. W.; Zhang, X.; Thai, Q. B.; Phan-Thien, N.; Duong, H. M., Methyltrimethoxysilane-coated recycled polyethylene terephthalate aerogels for oil spill cleaning applications. Materials Chemistry and Physics 2020, 239, 122064. 263. Sun, L.; Jiang, Z.; Yuan, B.; Zhi, S.; Zhang, Y.; Li, J.; Wu, A., Ultralight and superhydrophobic perfluorooctyltrimethoxysilane modified biomass carbonaceous aerogel for oil-spill remediation. Chemical Engineering Research and Design 2021, 174, 71-78. 264. Cheng, H.; Gu, B.; Pennefather, M. P.; Nguyen, T. X.; Phan-Thien, N.; Duong, H. M., Cotton aerogels and cotton-cellulose aerogels from environmental waste for oil spillage cleanup. Materials & Design 2017, 130, 452-458. 265. Pawar, A. A.; Kim, A.; Kim, H., Synthesis and performance evaluation of plastic waste aerogel as sustainable and reusable oil absorbent. Environmental Pollution 2021, 288, 117717. 266. He, J.; Zhao, H.; Li, X.; Su, D.; Zhang, F.; Ji, H.; Liu, R., Superelastic and superhydrophobic bacterial cellulose/silica aerogels with hierarchical cellular structure for oil absorption and recovery. Journal of Hazardous Materials 2018, 346, 199-207. 267. Zhou, L.; Xu, Z., Ultralight, highly compressible, hydrophobic and anisotropic lamellar carbon aerogels from graphene/polyvinyl alcohol/cellulose nanofiber aerogel as oil removing absorbents. Journal of Hazardous Materials 2020, 388, 121804. 268. Zhang, H.; Wang, J.; Xu, G.; Xu, Y.; Wang, F.; Shen, H., Ultralight, hydrophobic, sustainable, cost-effective and floating kapok/microfibrillated cellulose aerogels as speedy and recyclable oil superabsorbents. Journal of Hazardous Materials 2021, 406, 124758. 269. Renjith, P.; Sarathchandran, C.; Achary, V. S.; Chandramohanakumar, N.; Sekkar, V., Micro-cellular polymer foam supported silica aerogel: eco-friendly tool for petroleum oil spill cleanup. Journal of Hazardous Materials 2021, 415, 125548. 270. Dai, Y.; Jing, Z.; Qiu, Z.; Zhu, Y.; Qiu, F.; Pan, J.; Zhang, T.; Li, C., Multifunctional biomass carbon fiber aerogel based on resource utilization of agricultural waste-peanut shells for fast and efficient oil–water/emulsion separation. Materials Science and Engineering: B 2022, 283, 115819. 271. Yue, X.; Zhang, T.; Yang, D.; Qiu, F.; Li, Z., Hybrid aerogels derived from banana peel and waste paper for efficient oil absorption and emulsion separation. Journal of Cleaner Production 2018, 199, 411-419. 272. Wu, Y.; Huang, J.; Chen, J.; Li, D.; Shi, X.; Du, Y.; Deng, H., Ordered hollow nanofiber aerogel with revivability for efficient oil absorption. Journal of Cleaner Production 2021, 290, 125789. 273. Zhang, T.; Yuan, D.; Guo, Q.; Qiu, F.; Yang, D.; Ou, Z., Preparation of a renewable biomass carbon aerogel reinforced with sisal for oil spillage clean-up: Inspired by green leaves to green Tofu. Food and Bioproducts Processing 2019, 114, 154-162. 274. Jing, Z.; Ding, J.; Zhang, T.; Yang, D.; Qiu, F.; Chen, Q.; Xu, J., Flexible, versatility and superhydrophobic biomass carbon aerogels derived from corn bracts for efficient oil/water separation. Food and Bioproducts Processing 2019, 115, 134-142. 247 275. Wang, J.; Liu, S., Remodeling of raw cotton fiber into flexible, squeezing-resistant macroporous cellulose aerogel with high oil retention capability for oil/water separation. Separation and Purification Technology 2019, 221, 303-310. 276. Long, S.; Feng, Y.; Liu, Y.; Zheng, L.; Gan, L.; Liu, J.; Zeng, X.; Long, M., Renewable and robust biomass carbon aerogel derived from deep eutectic solvents modified cellulose nanofiber under a low carbonization temperature for oil-water separation. Separation and Purification Technology 2021, 254, 117577. 277. Hong, J. Y.; Sohn, E. H.; Park, S.; Park, H. S., Highly-efficient and recyclable oil absorbing performance of functionalized graphene aerogel. Chemical Engineering Journal 2015, 269, 229-235. 278. Yuan, D.; Zhang, T.; Guo, Q.; Qiu, F.; Yang, D.; Ou, Z., Recyclable biomass carbon@ SiO2@MnO2 aerogel with hierarchical structures for fast and selective oil-water separation. Chemical Engineering Journal 2018, 351, 622-630. 279. Wang, K.; Liu, X.; Tan, Y.; Zhang, W.; Zhang, S.; Li, J., Two-dimensional membrane and three-dimensional bulk aerogel materials via top-down wood nanotechnology for multibehavioral and reusable oil/water separation. Chemical Engineering Journal 2019, 371, 769-780. 280. Zhan, C.; Jana, S. C., Shrinkage reduced polyimide-graphene oxide composite aerogel for oil absorption. Microporous and Mesoporous Materials 2020, 307, 110501. 281. Xu, P.; Qian, P.; Yang, J.; Li, J.; Xia, Y.; Qian, W.; Duan, Z., Superhydrophobic and compressible carbon aerogels derived from platanus orientalis for oil absorption and emulsion separation. Journal of the Taiwan Institute of Chemical Engineers 2019, 103, 209-216. 282. Chatterjee, S.; Ke, W. T.; Liao, Y. C., Elastic nanocellulose/graphene aerogel with excellent shape retention and oil absorption selectivity. Journal of the Taiwan Institute of Chemical Engineers 2020, 111, 261-269. 283. Cheng, Y.; Xu, P.; Zeng, W.; Ling, C.; Zhao, S.; Liao, K.; Sun, Y.; Zhou, A., Highly hydrophobic and ultralight graphene aerogel as high efficiency oil absorbent material. Journal of Environmental Chemical Engineering 2017, 5 (2), 1957-1963. 284. Pawar, A. A.; Kim, H., Sustainable, hydrophobic, and reusable paper waste aerogel as an effective and versatile oil absorbent. Journal of Environmental Chemical Engineering 2022, 10 (2), 107356. 285. Zhou, S.; Jiang, W.; Wang, T.; Lu, Y., Highly hydrophobic, compressible, and magnetic polystyrene/Fe3O4/graphene aerogel composite for oil–water separation. Industrial & Engineering Chemistry Research 2015, 54 (20), 5460-5467. 286. Mi, H. Y.; Jing, X.; Huang, H. X.; Peng, X. F.; Turng, L. S., Superhydrophobic graphene/cellulose/silica aerogel with hierarchical structure as superabsorbers for high efficiency selective oil absorption and recovery. Industrial & Engineering Chemistry Research 2018, 57 (5), 1745-1755. 287. Yuan, D.; Zhang, T.; Guo, Q.; Qiu, F.; Yang, D.; Ou, Z., Superhydrophobic hierarchical biomass carbon aerogel assembled with TiO2 nanorods for selective immiscible oil/water mixture 248 and emulsion separation. Industrial & Engineering Chemistry Research 2018, 57 (43), 14758-14766. 288. Xu, X.; Dong, F.; Yang, X.; Liu, H.; Guo, L.; Qian, Y.; Wang, A.; Wang, S.; Luo, J., Preparation and characterization of cellulose grafted with epoxidized soybean oil aerogels for oil-absorbing materials. Journal of Agricultural and Food Chemistry 2019, 67 (2), 637-643. 289. Dai, C.; Sun, W.; Xu, Z.; Liu, J.; Chen, J.; Zhu, Z.; Li, L.; Zeng, H., Assembly of ultralight dual network graphene aerogel with applications for selective oil absorption. Langmuir 2020, 36 (45), 13698-13707. 290. Yang, Y.; Chen, X.; Li, Y.; Yin, Z.; Bao, M., Construction of a superhydrophobic sodium alginate aerogel for efficient oil absorption and emulsion separation. Langmuir 2021, 37 (2), 882-893. 291. Shi, G.; Wu, M.; Zhong, Q.; Mu, P.; Li, J., Superhydrophobic waste cardboard aerogels as effective and reusable oil absorbents. Langmuir 2021, 37 (25), 7843-7850. 292. Cai, C.; Wei, Z.; Huang, Y.; Ding, C.; Wang, P.; Song, J.; Deng, L.; Fu, Y.; Zhong, W., Ultralight programmable bioinspired aerogels with an integrated multifunctional surface for self-cleaning, oil absorption, and thermal insulation via coassembly. ACS Applied Materials & Interfaces 2020, 12 (9), 11273-11286. 293. Sai, H.; Fu, R.; Xing, L.; Xiang, J.; Li, Z.; Li, F.; Zhang, T., Surface modification of bacterial cellulose aerogels’ web-like skeleton for oil/water separation. ACS Applied Materials & Interfaces 2015, 7 (13), 7373-7381. 294. Mulyadi, A.; Zhang, Z.; Deng, Y., Fluorine-free oil absorbents made from cellulose nanofibril aerogels. ACS Applied Materials & Interfaces 2016, 8 (4), 2732-2740. 295. Li, L.; Hu, T.; Sun, H.; Zhang, J.; Wang, A., Pressure-sensitive and conductive carbon aerogels from poplars catkins for selective oil absorption and oil/water separation. ACS Applied Materials & Interfaces 2017, 9 (21), 18001-18007. 296. Ieamviteevanich, P.; Palaporn, D.; Chanlek, N.; Poo-arporn, Y.; Mongkolthanaruk, W.; Eichhorn, S. J.; Pinitsoontorn, S., Carbon nanofiber aerogel/magnetic core–shell nanoparticle composites as recyclable oil sorbents. ACS Applied Nano Materials 2020, 3 (4), 3939-3950. 297. Zhou, S.; Liu, P.; Wang, M.; Zhao, H.; Yang, J.; Xu, F., Sustainable, reusable, and superhydrophobic aerogels from microfibrillated cellulose for highly effective oil/water separation. ACS Sustainable Chemistry & Engineering 2016, 4 (12), 6409-6416. 298. Zhang, X.; Wang, H.; Cai, Z.; Yan, N.; Liu, M.; Yu, Y., Highly compressible and hydrophobic anisotropic aerogels for selective oil/organic solvent absorption. ACS Sustainable Chemistry & Engineering 2018, 7 (1), 332-340. 299. Li, Z.; Zhong, L.; Zhang, T.; Qiu, F.; Yue, X.; Yang, D., Sustainable, flexible, and superhydrophobic functionalized cellulose aerogel for selective and versatile oil/water separation. ACS Sustainable Chemistry & Engineering 2019, 7 (11), 9984-9994. 300. Zhu, Z.; Fu, S.; Lucia, L. A., A fiber-aligned thermal-managed wood-based superhydrophobic aerogel for efficient oil recovery. ACS Sustainable Chemistry & Engineering 2019, 7 (19), 16428-16439. 249 301. Zhu, H.; Chen, D.; Li, N.; Xu, Q.; Li, H.; He, J.; Lu, J., Graphene foam with switchable oil wettability for oil and organic solvents recovery. Advanced Functional Materials 2015, 25 (4), 597-605. 302. Bi, H.; Yin, Z.; Cao, X.; Xie, X.; Tan, C.; Huang, X.; Chen, B.; Chen, F.; Yang, Q.; Bu, X., Carbon fiber aerogel made from raw cotton: a novel, efficient and recyclable sorbent for oils and organic solvents. Advanced Materials 2013, 25 (41), 5916-5921. 303. Korhonen, J. T.; Kettunen, M.; Ras, R. H.; Ikkala, O., Hydrophobic nanocellulose aerogels as floating, sustainable, reusable, and recyclable oil absorbents. ACS Applied Materials & Interfaces 2011, 3 (6), 1813-1816. 304. Yang, Y.; Tong, Z.; Ngai, T.; Wang, C., Nitrogen-rich and fire-resistant carbon aerogels for the removal of oil contaminants from water. ACS Applied Materials & Interfaces 2014, 6 (9), 6351-6360. 305. Yun, S.; Luo, H.; Gao, Y., Superhydrophobic silica aerogel microspheres from methyltrimethoxysilane: rapid synthesis via ambient pressure drying and excellent absorption properties. RSC Advances 2014, 4 (9), 4535-4542. 306. Li, R.; Chen, C.; Li, J.; Xu, L.; Xiao, G.; Yan, D., A facile approach to superhydrophobic and superoleophilic graphene/polymer aerogels. Journal of Materials Chemistry A 2014, 2 (9), 3057-3064. 307. Jiang, F.; Hsieh, Y. L., Amphiphilic superabsorbent cellulose nanofibril aerogels. Journal of Materials Chemistry A 2014, 2 (18), 6337-6342. 308. Zhang, H.; Li, Y.; Xu, Y.; Lu, Z.; Chen, L.; Huang, L.; Fan, M., Versatile fabrication of a superhydrophobic and ultralight cellulose-based aerogel for oil spillage clean-up. Physical Chemistry Chemical Physics 2016, 18 (40), 28297-28306. 309. Shi, M.; Tang, C.; Yang, X.; Zhou, J.; Jia, F.; Han, Y.; Li, Z., Superhydrophobic silica aerogels reinforced with polyacrylonitrile fibers for adsorbing oil from water and oil mixtures. RSC Advances 2017, 7 (7), 4039-4045. 310. Wang, J.; Zhao, D.; Shang, K.; Wang, Y. T.; Ye, D. D.; Kang, A. H.; Liao, W.; Wang, Y. Z., Ultrasoft gelatin aerogels for oil contaminant removal. Journal of Materials Chemistry A 2016, 4 (24), 9381-9389. 311. Xu, Z.; Zhou, H.; Jiang, X.; Li, J.; Huang, F., Facile synthesis of reduced graphene oxide/trimethyl chlorosilane‐coated cellulose nanofibres aerogel for oil absorption. IET Nanobiotechnology 2017, 11 (8), 929-934. 312. Xu, Z.; Jiang, X.; Tan, S.; Wu, W.; Shi, J.; Zhou, H.; Chen, P., Preparation and characterisation of CNF/MWCNT carbon aerogel as efficient adsorbents. IET Nanobiotechnology 2018, 12 (4), 500-504. 313. Nie, X.; Lv, P.; Stanley, S. L.; Wang, D.; Wu, S.; Wei, Q., Ultralight nanocomposite aerogels with interpenetrating network structure of bacterial cellulose for oil absorption. Journal of Applied Polymer Science 2019, 136 (39), 48000. 314. Yin, Z.; Liu, W.; Bao, M.; Li, Y., Magnetic chitosan‐based aerogel decorated with polydimethylsiloxane: A high‐performance scavenger for oil in water. Journal of Applied Polymer Science 2021, 138 (20), 50461. 250 315. Zhao, D.; Yu, L.; Liu, D., Ultralight graphene/carbon nanotubes aerogels with compressibility and oil absorption properties. Materials 2018, 11 (4), 641. 316. Nguyen, D. D.; Vu, C. M.; Vu, H. T.; Choi, H. J., Micron-size white bamboo fibril-based silane cellulose aerogel: fabrication and oil absorbent characteristics. Materials 2019, 12 (9), 1407. 317. Li, Y.; Zhu, X.; Ge, B.; Men, X.; Li, P.; Zhang, Z., Versatile fabrication of magnetic carbon fiber aerogel applied for bidirectional oil–water separation. Applied Physics A 2015, 120 (3), 949-957. 318. Meng, Y.; Young, T. M.; Liu, P.; Contescu, C. I.; Huang, B.; Wang, S., Ultralight carbon aerogel from nanocellulose as a highly selective oil absorption material. Cellulose 2015, 22 (1), 435-447. 319. Mi, H. Y.; Li, H.; Jing, X.; Zhang, Q.; Feng, P. Y.; He, P.; Liu, Y., Superhydrophobic cellulose nanofibril/silica fiber/Fe3O4 nanocomposite aerogel for magnetically driven selective oil absorption. Cellulose 2020, 27 (15), 8909-8922. 320. He, S.; Cheng, X.; Li, Z.; Shi, X.; Yang, H.; Zhang, H., Green and facile synthesis of sponge-reinforced silica aerogel and its pumping application for oil absorption. Journal of Materials Science 2016, 51 (3), 1292-1301. 321. Feng, P.; Wang, X.; Yang, J., Highly compressible and hydrophobic anisotropic cellulose-based aerogel fabricated by bidirectional freeze-drying for selective oil absorption. Journal of Materials Science 2022, 57 (27), 13097-13108. 322. Li, Y. Q.; Samad, Y. A.; Polychronopoulou, K.; Alhassan, S. M.; Liao, K., Carbon aerogel from winter melon for highly efficient and recyclable oils and organic solvents absorption. ACS Sustainable Chemistry & Engineering 2014, 2 (6), 1492-1497. 323. Mi, H. Y.; Jing, X.; Politowicz, A. L.; Chen, E.; Huang, H. X.; Turng, L. S., Highly compressible ultra-light anisotropic cellulose/graphene aerogel fabricated by bidirectional freeze drying for selective oil absorption. Carbon 2018, 132, 199-209. 324. Liu, H.; Chen, X.; Zheng, Y.; Zhang, D.; Zhao, Y.; Wang, C.; Pan, C.; Liu, C.; Shen, C., Lightweight, superelastic, and hydrophobic polyimide nanofiber/MXene composite aerogel for wearable piezoresistive sensor and oil/water separation applications. Advanced Functional Materials 2021, 31 (13), 2008006. 325. Long, S.; Feng, Y.; He, F.; Zhao, J.; Bai, T.; Lin, H.; Cai, W.; Mao, C.; Chen, Y.; Gan, L., Biomass-derived, multifunctional and wave-layered carbon aerogels toward wearable pressure sensors, supercapacitors and triboelectric nanogenerators. Nano Energy 2021, 85, 105973. 326. Li, C.; Chen, Z.; Dong, W.; Lin, L.; Zhu, X.; Liu, Q.; Zhang, Y.; Zhai, N.; Zhou, Z.; Wang, Y., A review of silicon-based aerogel thermal insulation materials: performance optimization through composition and microstructure. Journal of Non-Crystalline Solids 2021, 553, 120517. 327. Apostolopoulou‐Kalkavoura, V.; Munier, P.; Bergström, L., Thermally insulating nanocellulose‐based materials. Advanced Materials 2021, 33 (28), 2001839. 328. Hu, P.; Wang, J.; Zhang, P.; Wu, F.; Cheng, Y.; Wang, J.; Sun, Z., Hyperelastic kevlar nanofiber aerogels as robust thermal switches for smart thermal management. Advanced Materials 2022, e2207638. 251 329. Panahi‐Sarmad, M.; Samsami, S.; Ghaffarkhah, A.; Hashemi, S. A.; Ghasemi, S.; Amini, M.; Wuttke, S.; Rojas, O.; Tam, K. C.; Jiang, F.; Arjmand, M.; Ahmadijokani, F.; Kamkar, M., MOF‐based electromagnetic shields multiscale design: nanoscale chemistry, microscale assembly, and macroscale manufacturing. Advanced Functional Materials 2023, 2304473. 330. Wanasinghe, D.; Aslani, F., A review on recent advancement of electromagnetic interference shielding novel metallic materials and processes. Composites Part B: Engineering 2019, 176, 107207. 331. Wang, X. X.; Zheng, Q.; Zheng, Y. J.; Cao, M. S., Green EMI shielding: dielectric/magnetic “genes” and design philosophy. Carbon 2023, 206, 124-141. 332. Kumar, R.; Sahoo, S.; Joanni, E.; Singh, R. K.; Tan, W. K.; Kar, K. K.; Matsuda, A., Recent progress on carbon-based composite materials for microwave electromagnetic interference shielding. Carbon 2021, 177, 304-331. 333. Kruželák, J.; Kvasničáková, A.; Hložeková, K.; Hudec, I., Progress in polymers and polymer composites used as efficient materials for EMI shielding. Nanoscale Advances 2021, 3 (1), 123-172. 334. Zhang, Y.; Ruan, K.; Zhou, K.; Gu, J., Controlled distributed Ti3C2Tx hollow microspheres on thermally conductive polyimide composite films for excellent electromagnetic interference shielding. Advanced Materials 2023, 35 (16), 2211642. 335. Zhao, B.; Hamidinejad, M.; Wang, S.; Bai, P.; Che, R.; Zhang, R.; Park, C. B., Advances in electromagnetic shielding properties of composite foams. Journal of Materials Chemistry A 2021, 9 (14), 8896-8949. 336. Zhao, Z.; Zhang, L.; Wu, H., Hydro/organo/ionogels:“controllable” electromagnetic wave absorbers. Advanced Materials 2022, 34 (43), 2205376. 337. Lee, K. Y.; Mahadik, D. B.; Parale, V. G.; Park, H. H., Composites of silica aerogels with organics: A review of synthesis and mechanical properties. Journal of the Korean Ceramic Society 2020, 57, 1-23. 338. Zuo, T.; Wang, W.; Yu, D., MXene/Ag@ZnO/WPU/Melamine gradient composite foams prepared by a unidirectional evaporation approach for absorption-dominated electromagnetic interference shielding. Journal of Alloys and Compounds 2023, 966, 171644. 339. Yan, P.; Yujia, H.; Qi, W.; Yong, Z.; Guangsu, H.; Qichao, R.; Jinrong, W., Recyclable, self-healing, absorption-dominated and highly effective electromagnetic shielding elastomers based on bridged micro capacitance structures. Carbon 2020, 166, 56-63. 340. Miao, P.; Qu, N.; Chen, W.; Wang, T.; Zhao, W.; Kong, J., A two-dimensional semiconductive Cu-S metal-organic framework for broadband microwave absorption. Chemical Engineering Journal 2023, 454, 140445. 341. Miao, P.; Zhou, R.; Chen, K.; Liang, J.; Ban, Q.; Kong, J., Tunable electromagnetic wave absorption of supramolecular isomer‐derived nanocomposites with different morphology. Advanced Materials Interfaces 2020, 7 (4), 1901820. 342. Miao, P.; Zhang, T.; Wang, T.; Chen, J.; Gao, T.; Wang, Y.; Kong, J.; Chen, K. J., A Two‐dimensional semiconductive metal‐organic framework for highly efficient microwave absorption. Chinese Journal of Chemistry 2022, 40 (4), 467-474. 252 343. Ma, L.; Wei, L.; Hamidinejad, M.; Park, C. B., Layered polymer composite foams for broadband ultra-low reflectance EMI shielding: a computationally guided fabrication approach. Materials Horizons 2023, 10 (10), 4423-4437. 344. Feng, L.; Wei, P.; Song, Q.; Zhang, J.; Fu, Q.; Jia, X.; Yang, J.; Shao, D.; Li, Y.; Wang, S., Superelastic, highly conductive, superhydrophobic, and powerful electromagnetic shielding hybrid aerogels built from orthogonal graphene and boron nitride nanoribbons. ACS Nano 2022, 16 (10), 17049-17061. 345. Wu, S.; Chen, D.; Han, W.; Xie, Y.; Zhao, G.; Dong, S.; Tan, M.; Huang, H.; Xu, S.; Chen, G., Ultralight and hydrophobic MXene/chitosan-derived hybrid carbon aerogel with hierarchical pore structure for durable electromagnetic interference shielding and thermal insulation. Chemical Engineering Journal 2022, 446, 137093. 346. Li, Y.; Meng, F.; Mei, Y.; Wang, H.; Guo, Y.; Wang, Y.; Peng, F.; Huang, F.; Zhou, Z., Electrospun generation of Ti3C2Tx MXene@graphene oxide hybrid aerogel microspheres for tunable high-performance microwave absorption. Chemical Engineering Journal 2020, 391, 123512. 347. Wang, Y.; Han, X.; Xu, P.; Liu, D.; Cui, L.; Zhao, H.; Du, Y., Synthesis of pomegranate-like Mo2C@C nanospheres for highly efficient microwave absorption. Chemical Engineering Journal 2019, 372, 312-320. 348. Li, M.; Han, F.; Jiang, S.; Zhang, M.; Xu, Q.; Zhu, J.; Ge, A.; Liu, L., Lightweight cellulose nanofibril/reduced graphene oxide aerogels with unidirectional pores for efficient electromagnetic interference shielding. Advanced Materials Interfaces 2021, 8 (24), 2101437. 349. Jian, X.; Wu, B.; Wei, Y.; Dou, S. X.; Wang, X.; He, W.; Mahmood, N., Facile synthesis of Fe3O4/GCs composites and their enhanced microwave absorption properties. ACS Applied Materials & Interfaces 2016, 8 (9), 6101-6109. 350. Quan, B.; Shi, W.; Ong, S. J. H.; Lu, X.; Wang, P. L.; Ji, G.; Guo, Y.; Zheng, L.; Xu, Z. J., Defect engineering in two common types of dielectric materials for electromagnetic absorption applications. Advanced Functional Materials 2019, 29 (28), 1901236. 351. Wan, Y.; Xiong, P.; Liu, J.; Feng, F.; Xun, X.; Gama, F. M.; Zhang, Q.; Yao, F.; Yang, Z.; Luo, H., Ultrathin, strong, and highly flexible Ti3C2Tx MXene/bacterial cellulose composite films for high-performance electromagnetic interference shielding. ACS Nano 2021, 15 (5), 8439-8449. 352. Sun, Y.; Han, X.; Guo, P.; Chai, Z.; Yue, J.; Su, Y.; Tan, S.; Sun, X.; Jiang, L.; Heng, L., Slippery graphene-bridging liquid metal layered heterostructure nanocomposite for stable high-performance electromagnetic interference shielding. ACS Nano 2023. 353. Peng, F.; Zhu, W.; Fang, Y.; Fu, B.; Chen, H.; Ji, H.; Ma, X.; Hang, C.; Li, M., Ultralight and highly conductive silver nanowire aerogels for high-performance electromagnetic interference shielding. ACS Applied Materials & Interfaces 2023, 15 (3), 4284-4293. 354. Xia, S.; Wei, C.; Tang, J.; Yan, J., Tensile stress-gated electromagnetic interference shielding fabrics with real-time adjustable shielding efficiency. ACS Sustainable Chemistry & Engineering 2021, 9 (42), 13999-14005. 253 355. Hashemi, S. A.; Ghaffarkhah, A.; Ahmadijokani, F.; Yousefian, H.; Mhatre, S. E.; Sinelshchikova, A.; Banvillet, G.; Kamkar, M.; Rojas, O. J.; Wuttke, S.; Arjmand, M., Liquid-templated graphene aerogel electromagnetic traps. Nanoscale 2024. 356. Wicklein, B.; Kocjan, A.; Salazar-Alvarez, G.; Carosio, F.; Camino, G.; Antonietti, M.; Bergström, L., Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide. Nature Nanotechnology 2015, 10 (3), 277-283. 357. Lo, T. H.; Yu, S. S., 3D printable and sub‐micrometer porous polymeric monoliths with shape reconfiguration ability by miniemulsion templating. Macromolecular Materials and Engineering 2022, 307 (1), 2100615. 358. Zhou, L. Y.; Fu, J.; He, Y., A review of 3D printing technologies for soft polymer materials. Advanced Functional Materials 2020, 30 (28), 2000187. 359. Saadi, M.; Maguire, A.; Pottackal, N. T.; Thakur, M. S. H.; Ikram, M. M.; Hart, A. J.; Ajayan, P. M.; Rahman, M. M., Direct ink writing: a 3D printing technology for diverse materials. Advanced Materials 2022, 34 (28), 2108855. 360. Orangi, J.; Hamade, F.; Davis, V. A.; Beidaghi, M., 3D printing of additive-free 2D Ti3C2Tx (MXene) ink for fabrication of micro-supercapacitors with ultra-high energy densities. ACS Nano 2019, 14 (1), 640-650. 361. Amini, M.; Kamkar, M.; Ahmadijokani, F.; Ghaderi, S.; Rojas, O. J.; Hosseini, H.; Arjmand, M., Mapping 3D printability of ionically cross-linked cellulose nanocrystal inks: architecting from nano-to macroscale structures. Biomacromolecules 2022, 24 (2), 775-788. 362. Zhou, J.; Wu, X.; Chen, Y.; Yang, C.; Yang, R.; Tan, J.; Liu, Y.; Qiu, L.; Cheng, H. M., 3D printed template‐directed assembly of multiscale graphene structures. Advanced Functional Materials 2022, 32 (18), 2105879. 363. Minas, C.; Carnelli, D.; Tervoort, E.; Studart, A. R., 3D printing of emulsions and foams into hierarchical porous ceramics. Advanced Materials 2016, 28 (45), 9993-9999. 364. Sears, N. A.; Dhavalikar, P. S.; Cosgriff‐Hernandez, E. M., Emulsion inks for 3D printing of high porosity materials. Macromolecular Rapid Communications 2016, 37 (16), 1369-1374. 365. Karamikamkar, S.; Naguib, H. E.; Park, C. B., Advances in precursor system for silica-based aerogel production toward improved mechanical properties, customized morphology, and multifunctionality: A review. Advances in Colloid and Interface Science 2020, 276, 102101. 366. Amini, M.; Hosseini, H.; Dutta, S.; Wuttke, S.; Kamkar, M.; Arjmand, M., Surfactant-mediated highly conductive cellulosic inks for high-resolution 3D printing of robust and structured electromagnetic interference shielding aerogels. ACS Applied Materials & Interfaces 2023, 15 (47), 54753-54765. 367. Hausmann, M. K.; Ruhs, P. A.; Siqueira, G.; Läuger, J. r.; Libanori, R.; Zimmermann, T.; Studart, A. R., Dynamics of cellulose nanocrystal alignment during 3D printing. ACS Nano 2018, 12 (7), 6926-6937. 368. Schwab, A.; Levato, R.; D’Este, M.; Piluso, S.; Eglin, D.; Malda, J., Printability and shape fidelity of bioinks in 3D bioprinting. Chemical Reviews 2020, 120 (19), 11028-11055. 254 369. Ching, Y. C.; Ershad Ali, M.; Abdullah, L. C.; Choo, K. W.; Kuan, Y. C.; Julaihi, S. J.; Chuah, C. H.; Liou, N. S., Rheological properties of cellulose nanocrystal-embedded polymer composites: a review. Cellulose 2016, 23, 1011-1030. 370. Amoroso, L.; Muratore, G.; Ortenzi, M. A.; Gazzotti, S.; Limbo, S.; Piergiovanni, L., Fast production of cellulose nanocrystals by hydrolytic-oxidative microwave-assisted treatment. Polymers 2020, 12 (1), 68. 371. Ureña-Benavides, E. E.; Kitchens, C. L., Wide-angle X-ray diffraction of cellulose nanocrystal−alginate nanocomposite fibers. Macromolecules 2011, 44 (9), 3478-3484. 372. Azrina, Z. Z.; Beg, M. D. H.; Rosli, M.; Ramli, R.; Junadi, N.; Alam, A. M., Spherical nanocrystalline cellulose (NCC) from oil palm empty fruit bunch pulp via ultrasound assisted hydrolysis. Carbohydrate Polymers 2017, 162, 115-120. 373. Kumar, A.; Negi, Y. S.; Choudhary, V.; Bhardwaj, N. K., Characterization of cellulose nanocrystals produced by acid-hydrolysis from sugarcane bagasse as agro-waste. Journal of Materials Physics and Chemistry 2014, 2 (1), 1-8. 374. Liang, H. W.; Guan, Q. F.; Chen, L. F.; Zhu, Z.; Zhang, W. J.; Yu, S. H., Macroscopic‐scale template synthesis of robust carbonaceous nanofiber hydrogels and aerogels and their applications. Angewandte Chemie International Edition 2012, 51 (21), 5101-5105. 375. Yang, X.; Cranston, E. D., Chemically cross-linked cellulose nanocrystal aerogels with shape recovery and superabsorbent properties. Chemistry of Materials 2014, 26 (20), 6016-6025. 376. Shin, S.; Hyun, J., Rheological properties of cellulose nanofiber hydrogel for high-fidelity 3D printing. Carbohydrate Polymers 2021, 263, 117976. 377. Zhuo, H.; Hu, Y.; Chen, Z.; Peng, X.; Lai, H.; Liu, L.; Liu, Q.; Liu, C.; Zhong, L., Linking renewable cellulose nanocrystal into lightweight and highly elastic carbon aerogel. ACS Sustainable Chemistry & Engineering 2020, 8 (32), 11921-11929. 378. Zhu, J.; Zhu, Y.; Ye, Y.; Qiu, Z.; Zhang, Y.; Yu, Z.; Sun, X.; Bressler, D. C.; Jiang, F., Superelastic and ultralight aerogel assembled from hemp microfibers. Advanced Functional Materials 2023, 33 (22), 2300893. 379. Liang, L.; Li, Q.; Yan, X.; Feng, Y.; Wang, Y.; Zhang, H. B.; Zhou, X.; Liu, C.; Shen, C.; Xie, X., Multifunctional magnetic Ti3C2Tx MXene/graphene aerogel with superior electromagnetic wave absorption performance. ACS Nano 2021, 15 (4), 6622-6632. 380. Yao, C.; Yi, J.; Lai, H.; Shi, G.; Hu, Y.; Chen, Z.; Zhai, J.; Wang, X.; Zhong, L.; Liu, C., Enhancing the mechanical performance of reduced graphene oxide aerogel with cellulose nanofibers. ChemNanoMat 2021, 7 (8), 950-957. 381. Guo, L.; Chen, Z.; Lyu, S.; Fu, F.; Wang, S., Highly flexible cross-linked cellulose nanofibril sponge-like aerogels with improved mechanical property and enhanced flame retardancy. Carbohydrate Polymers 2018, 179, 333-340. 382. Li, Y.; Grishkewich, N.; Liu, L.; Wang, C.; Tam, K. C.; Liu, S.; Mao, Z.; Sui, X., Construction of functional cellulose aerogels via atmospheric drying chemically cross-linked and solvent exchanged cellulose nanofibrils. Chemical Engineering Journal 2019, 366, 531-538.
Thesis/Dissertation
eng
Mechanical Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Arjmand, Mohammad
From interfacially complexed structured liquids to electromagnetic shielding aerogels
Text