Dynamic Structural Colors in Cholesteric Cellulose Composites: Achieving Spatial and Temporal Control

Abstract

Structurally-colored cholesteric cellulose ether materials offer a sustainable alternative to traditionally-dyed plastics. These materials are produced by dissolving high concentrations of cellulosic polymers in a monomeric solvent, forming a liquid crystalline mesophase, and polymerizing to kinetically trap the ordered arrangement in a composite. Despite significant advancements in fabricating colorimetric films and devices using this method, the lack of critical design rules for predicting color evolution upon polymerization hinders large-scale deployment and rational design. In this work, ethyl cellulose-poly(acrylic acid) films are used as a model system to explore how the balance between polymer chain mobility and solvent photopolymerization kinetics affect the preservation of cholesteric texture and optical properties. These findings reveal that the observed blue-shift in reflectivity is linked to the realignment or disruption of chiral nematic order during poly(acrylic acid) chain growth. Time-resolved studies during UV curing, including in situ reflection spectroscopy and rheometry, demonstrate that rapid polymerization and reduced polysaccharide mobility are key to maintaining the color and angle-dependent optical appearance in the final films. Applying these fundamental design principles, we create composites with spatially-controlled photopatterned colors, tailored angle-resolved reflectivity that resists photobleaching, and reversible colorimetric functions that are unattainable with pigmented plastics.