UBC Theses and Dissertations
Functional materials from cellulose nanocrystals Walters, Christopher Michael
The synthesis, characterization, and application of several materials with long range hierarchical ordering derived from cellulose nanocrystals (CNCs) is reported. CNCs are an interesting nanomaterial to work with owing to their chiral nematic liquid crystalline behaviour that is observed above a critical concentration. This property makes CNCs attractive for materials development as they can be used to direct the organization of other materials introducing long range order into substrates that do not traditionally possess order. Importantly, CNCs are an inexpensive, renewable, and biodegradable resource that can be exploited in the development of new nanomaterials. Although CNCs have impressive mechanical properties, they form intrinsically brittle materials. To address this, composites of CNCs and hydroxypropyl cellulose (HPC) were prepared. The inclusion of HPC enabled the modulation of mechanical and optical properties with increasing polymer content and molecular weight. Surface functionalization of the materials increased their hydrophobicity, addressing a common problem that limits the application of such composite materials. This work serves to deepen our understanding of molecular additives on CNC self assembly as well as demonstrates how CNC films can be modified for more practical applications such as in coatings and packaging. Extending beyond this, chiral nematic mesoporous silica (CNMS) – formed from CNCs – was used to form a variety of CNMS metal composite materials (metal = CuO, Cu, ZnO, Au, Ag, Ag/Cu). Selective removal of the silica afforded materials with a variety of nanostructures. Focusing on the materials which retained long range order, I demonstrated they could be used as catalysts. This work highlights of promise for ordered metal materials for high surface area applications such as in catalysis or separation. The development of CNC based aerogel materials for energy storage applications was also explored. CNCs provide a suitable scaffold to direct the assembly of metal precursors, and when incorporated into aerogels provides a lightweight, high surface area substrate that is a promising candidate for inclusion in supercapacitors. Chiral nematic CNC/germania and carbon/germania composites were prepared and when used as the electrodes in both symmetric and solid state symmetric supercapacitors showed good capacitance and cycling stability. This exciting discovery further cements the benefit of using renewable materials in high value applications.
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