Effect of Polymerization on Chirality in Cholesteric Liquid Crystals

Cholesteric liquid crystals (CLCs) possess a periodic helical structure and exhibit selective reflection. When monomeric CLCs are polymerized, they form polymeric CLC films, which have many important applications, thanks to their unique optical property, chemical and thermal stability, and mechanical strength. The helical structure may change during polymerization. We carried out an experiment to study the effects of polymerization on the helical structure. We found that in systems consisting of achiral monomers, or a combination of achiral and chiral monomers, the helical structure is preserved in the polymerization, while in systems consisting only of chiral monomers, the helical structure may be destroyed by the polymerization, depending on the polymerization speed. We investigated the mechanism of the change of chirality in the polymerization and found a way to fabricate polymeric CLC films with desired optical properties. We also studied the morphology of the polymer network formed in CLCs and observed that it depends on the curing UV light intensity, photoinitiator, and the chirality of the host liquid crystal. Dense polymer networks with small lateral sizes are formed under high UV light intensity and high photoinitiator concentration, which can freeze the helical structure of the CLC.