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Chiral nematic mesoporous materials templated by nanocrystalline cellulose Shopsowitz, Kevin Eric


The synthesis, characterization, and application of the first examples of chiral nematic mesoporous materials are reported. Nanocrystalline cellulose (NCC) was used as a liquid crystal template to generate NCC/silica composite films through evaporation induced self-assembly. The NCC was removed from the composite films by calcination to generate mesoporous silica films with high specific surface areas and chiral nematic structures. The chiral nematic ordering in these films gives rise to photonic properties that can be tuned depending on the synthetic conditions. Thus mesoporous silica films with colours spanning the visible spectrum were synthesized. The combination of mesoporosity and chiral nematic ordering in these materials causes them to change colour in response to liquids and show strong circular dichroism signals that depend on the refractive index within the mesopores. Chiral nematic mesoporous silica can also be used as a hard template to generate nanocrystalline films of anatase titanium dioxide. The titanium dioxide replicas are mesoporous and show chiral nematic ordering and photonic properties that mimic the original silica films. By exploring different methods to remove NCC from the composite films, the procedure used to synthesize chiral nematic mesoporous silica films was expanded to organosilica. The resulting chiral nematic mesoporous organosilica films show similar properties to the mesoporous silica films but have superior flexibility in some cases. Methods to control the pore size of the mesoporous silica and organosilica materials were developed. Nanocrystalline cellulose/silica composite films were also used as a starting point to synthesize chiral nematic mesoporous carbon films. This was achieved by pyrolyzing NCC/silica composite films followed by dissolving the silica in strong base. The silica used in this procedure was shown to be necessary for both the retention of chiral nematic ordering and the introduction of mesoporosity into the carbonaceous material. Finally, chiral nematic mesoporous carbon (CNMC) was shown to be a promising material as a supercapacitor electrode material both on its own and as a composite with polyaniline.

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