Cellulose Nanocrystals for Humidity Actuator with Incident Angle-Responsive Circularly Polarized Reflectance

Chiral nematic cellulose nanocrystal films are one-dimensional photonic crystals, which receive a lot of attention in many fields, including visible sensors and actuators, anticounterfeiting, iridescent coatings, and other photonic materials that profit from the unique optical properties. Herein, we report a dual-actuated bilayer film of cellulose nanocrystals and graphene oxide for circular polarization encryption. The bilayer structure is capable of reversible shape deformation in response to humidity and NIR irradiation, accompanied by tunable circular polarization properties. The shape deformation generates the band gap of cellulose nanocrystal layer blue shift with the increase of incident light angle, and the peak wavelength of the cellulose nanocrystal layer no longer matches the original photosource. Different patterns appear on the degree of circular polarization (DOCP) distribution map resulting from incident angle-dependent circularly polarized reflection. The cellulose nanocrystal-based bilayer film shows unique potential for circular polarization display of humidity actuators.