Cholesteric liquid crystal polymer network film exhibiting broad or dual reflection bands induced by molecular migration during annealing

Abstract

Cholesteric liquid crystal polymer network (CLCN) films featuring broad or dual reflection bands have garnered significant attention in the fields of decoration and display technology. Such films can be constructed via molecular migration during the fabrication process. In this study, CLCN films were synthesized using diacrylate monomers through a two-step photopolymerization strategy, eliminating the need for non-reactive or low-reactive compounds to facilitate molecular migration. Based on oxygen inhibition, monomers in the bottom and top layers of the film were polymerized sequentially in the first and second steps, respectively. As the annealing interval between the two polymerization steps was extended, the initial single reflection band gradually broadened before splitting into distinct dual bands. This phenomenon is hypothesized to be driven by the migration of unreacted monomers from the top layer to the bottom layer. Building on this two-step polymerization approach, colourful patterns with composite structural colours were successfully fabricated. Additionally, a patterned linear polarizer was developed, which allows the encoded patterns to be visualized under linearly polarized light. By stacking this patterned polarizer with a patterned CLCN film, an encrypted composite film was created. These findings not only deepen our understanding of how molecular migration modulates the helical pitch of CLCN films but also establish a foundational framework for their practical applications in advanced decoration, next-generation displays, and optical encryption systems.