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Xu, Yitao

University of British Columbia

Cellulose nanocrystals (CNCs) and graphene oxide (GO) can self-assemble into chiral nematic and lamellar (or nematic) liquid crystals, respectively; this offers an opportunity to introduce large-scale ordered structures into different assembled systems. This thesis focused on the introduction of chiral nematic and lamellar structure into aerogels, films, hydrogel microbeads, and suspensions. The self-assembly behavior of GO in confined geometry and in the presence of additives was also studied. Chiral nematic aerogels were developed. Through a solvent-exchanged method and silica condensation reaction, the chiral nematic liquid crystalline structure of CNCs was captured to produce CNC and CNC-silica alcogels. Both the chiral nematic CNC and CNC-silica aerogels were obtained after supercritical drying of their alcohol gels, and subsequent calcination of CNC-silica aerogels afforded silica aerogels with chiral nematic structure. To improve the mechanical performance and optical stability of chiral nematic CNC materials in water, CNCs were combined with epoxy resins to make composites with hydrogen-bonded/covalent dual networks. These composites not only displayed tunable chiral photonic properties, but also the ability to adapt their stiffness and toughness upon exposure to water. The changeable mechanical properties are related to the on/off switch of inter-CNC interactions. The self-assembly behavior of GO in spherical space was investigated. The arrangement of GO nanosheets was captured by inverse emulsion photopolymerization to form hydrogel microspheres. GO nanosheets in spherical confined space can form a concentric or pseudo-concentric structure. The effect of additives on iridescent GO photonic liquids was investigated. Colloidal additives added to GO suspensions led to dramatic color changes. On the other hand, blending polymeric or molecular additives with GO suspensions either deteriorated or did not impact the photonic properties. The phenomenon from hybrid colloidal photonic suspensions was explained by the depletion interaction between particles. Stable GO hydrophobic photonic liquids were developed. GO were directed into different hydrophobic organic solvents using phase transfer additives. The obtained GO liquids exhibit tunable reflection colors with improved stability relative to aqueous GO photonic suspensions at elevated temperatures or under ambient conditions. Furthermore, simultaneous infrared and visible light reflection can be achieved, enabling infrared photonic GO liquids to display visible colors.

Text

2023-01-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/80734

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/