Better Understanding of the Composite Colored Cholesteric Liquid Crystal Polymer Network Film Prepared through Polymerization-Induced Chiral Dopant Diffusion

Cholesteric liquid crystal polymer network (CLCN) patterns featuring double helical pitches are attractive for decoration and anticounterfeiting. Herein, the polyacrylate-based CLCN films with double helical pitches were fabricated utilizing a nonreactive chiral dopant via a two-step photopolymerization approach. At the first step, a cholesteric liquid crystal (CLC) mixture was irradiated using the 365 nm LED lamp with a low light intensity. Based on oxygen inhibition, only the acrylate molecules near the substrate surface were polymerized. This polymerization caused the chiral dopant to diffuse from the bottom to the top section of the CLC mixture. Then, the structure with double helical pitches was formed. The diffusion of the chiral dopant was time-dependent. During the second step, this structure was stabilized following irradiation with a high-pressure Hg lamp (1.0 kW). When the chiral dopant was reactive, the Bragg reflection band of the CLCN film was broadened, which was proposed to be driven by the diffusion of the nematic liquid crystal. Moreover, patterns exhibiting composite structural colors were prepared, with potential applications in decoration.