Flexible patterned mirrors prepared by stacking patterned cholesteric liquid crystal polymer network films†

Abstract

Cholesteric liquid crystal polymer network (CLCN) mirrors attract much attention for the potential applications as optical filters and for decoration. For the preparation of CLCN films, the chiral additives with a high helical twisting power value are essential. Herein, a series of chiral additives was synthesized using isosorbide and 4-(trans-4-n-alkylcyclohexyl)benzoic acids. With increasing the alkyl chain length, the solubility of the chiral dopant decreased in the CLC mixtures. Since the solubility of the chiral additive with two n-pentyl chains is sensitive to temperature, the CLC mixture containing this additive exhibits the thermochromic property. Several CLCN films were prepared using the chiral dopant with two ethyl chains or S5011. Then, the CLCN mirrors were prepared by stacking these CLCN films using an optically clear adhesive. For the patterned CLCN mirror prepared using the CLCN films with opposite handedness, colourful images are observed through circular polarizers, which can be applied for encryption.