UBC Theses and Dissertations
Switching the reflection in chiral nematic mesoporous silica and organosilica films De Witt, Joanna Christine
Recently, a new class of free-standing chiral nematic mesoporous silica and organosilica films was developed using nanocrystalline cellulose as a template. Due to their unique structures these films are iridescent, and by varying synthetic conditions it has been shown that this iridescence can be tuned to selectively reflect incident light of different wavelengths across the entire visible spectrum. However, upon formation of the mesostructure, these optical properties are locked in and can no longer be altered. Herein I describe alternate techniques to modify the optical properties of these silica and organosilica films by infiltration with guest molecules after the films have been prepared. Liquid crystal mesogen 5CB and 8CB were loaded into the pores of unfunctionalized and octyl and phenyl functionalized silica films. Thermal cycling of these new composite materials elucidated a sharp and reversible optical change in the 8CB loaded octyl functionalized silica films. Additional studies including variable temperature POM and UV-Vis spectroscopy were conducted on this system prepared with organosilica films. This approach was then expanded on by doping an azobenzene derivative in 1, 5, and 10 % by weight into the 8CB liquid crystal before loading the mixtures into the films. A reversible optical change was then brought about in this system by irradiation at different wavelengths. Further development of these methods could lead to their implementation in the still emerging fields of sensing and display technologies involving colour information.
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