Photonic Properties and Applications of Cellulose Nanocrystal Films with Planar Anchoring

Above a critical concentration, aqueous dispersions of sulfonated cellulose nanocrystals (CNC) form chiral nematic liquid crystalline phases. Retention of microstructural order and planar anchoring of the helix during drying should result in films that exhibit selective reflection of specific wavelengths of light. Such films are of interest for use in a variety of photonic applications including display components, narrow band optical filters, low-threshold mirrorless lasing, sensors, and architectural, decorative, and security coatings. However, nonuniformities in the initial CNC dispersions and microstructural changes during drying typically result in uniform selective reflection only being achieved over length scales on the order of tens of microns. In this research, uniform photonic properties were achieved over orders of magnitude greater length scales by understanding the effects of initial concentration, orbital shear, surface anchoring, and drying conditions on films' microstructure and photonic properties. In addition, biomimetic films were produced which exhibited a double-peak spectra similar to that exhibited by the chiral nematic photonic structure in Lomaptera beetles.