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

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.