Visual appearance of chiral nematic cellulose-based photonic films: Angular and polarization independent color response with a twist

Abstract

Hydroxypropyl cellulose (HPC) is a biocompatible and rewewable resource derived from cellulose. In aqueous solution, it is capable of self-assembling into a lyotropic chiral nematic phase, which reflects right-handed circular polarized light of a particular wavelength and can thereby exhibit structural color. The specific color reflected can be tuned through various parameters, including temperature, ionic strength and most importantly, HPC weight fraction. In this study, we demonstrate that, by introducing a crosslinking agent, we can drastically alter the visual appearance of the HPC mesophase. Not only can we control the reflected color, we are able to tune the scattering properties of the chiral nematic system, resulting in solid-state films with a matte appearance. Furthermore, the polarization response is now altered in such a way that the system can now reflect both right and left-handed light. Such angular and polarization dependence is a highly demanded property within the pigment industry, and one which is difficult to achieve via structural coloration. As a result, developing a robust methodology towards such a system is an important step towards the development of HPC as a real-world photonic colorant.