Polymerization-induced diffusion-driven formation of a cholesteric liquid crystal polymer network film with double helical pitches

Abstract

Cholesteric liquid crystal polymer network (CLCN) films with a composite structural colour are attractive for application in decoration. Herein, CLCN films with double helical pitches were prepared using a non-reactive chiral dopant through photopolymerization. The polymerization-induced chiral dopant diffusion and oxygen inhibition played important roles in the formation of this structure. The diffusion of the chiral dopant was confirmed using the obtained energy dispersive spectrometry image. This diffusion drove the helical pitch of the top section shorter than that of the bottom section. Since the viscosity of the cholesteric liquid crystal mixture decreases with increasing temperature, the chiral dopant feasibly migrates at a hotter temperature. Therefore, the distance between the two reflectance bands of the CLCN film increased with increasing temperature. Colourful CLCN patterns were prepared through screen and inkjet printings, and were expected to be applied in the fields of decoration and anti-counterfeiting.