Memorizable Electro‐Birefringence Effect Exhibited by Transparent Liquid Crystal/Polymer Composite Materials

Abstract

Polymer‐dispersed liquid crystals (PDLCs) with nano‐phase‐separated structures, in which nanometer‐sized liquid crystal (LC) domains are dispersed within a polymer matrix (nano‐PDLCs), are transparent solid materials whose optical properties can be modulated by applying an electric field (E‐field). Because the proportion of LC that can respond to an electric field is small, the specific surface area of the phase‐separated interface of nano‐PDLCs is larger than that of conventional PDLCs, resulting in higher drive voltages than those of conventional PDLCs. To lower the driving voltage of nano‐PDLCs, highly polar LCs (C3DIO) are used with a large dielectric anisotropy (>10000), and prepared nano‐PDLCs using DIO mixtures obtained by mixing them with related compounds as the host LC. Nano‐PDLCs employing DIO mixtures exhibit higher E‐field responsivity than those using conventional LC. In addition, the electro‐optical Kerr coefficient at visible wavelength is significantly high, reaching 10−8 m V−2. Furthermore, nano‐PDLCs using the DIO mixture exhibit a memory effect in which the induced birefringence remains even after the removal of the in‐plane E‐field. Memorized birefringence can be erased by heating or applying an E‐field perpendicular to the substrate surface. Nano‐PDLCs using a DIO mixture can be rewritable electro‐birefringence‐responsive materials that can memorize arbitrary birefringence values.