Polymerization and thermal quench induced phase separation in polymer dispersed nematic liquid crystals

Abstract

The results of recent work on polymer dispersed liquid crystals formed by phase separation are presented with emphasis on the dynamics of phase separation. The kinetics of phase separation due to polymerization has been examined on an epoxy and monomeric liquid crystal (E7) system by studying the time evolution of the structure factor. Liquid—liquid phase separation and the isotropic nematic phase transition were explored in a polymer dispersed liquid crystal (PDLC) system of atactic polymethyl methacrylate and E7. A temperature versus composition phase diagram was established by means of cloud point method. The isotropic nematic transition was determined by depolarized light scattering and differential scanning calorimetry. The phase diagram consists three distinct regions: isotropic single phase region, coexisting isotropic liquid—isotropic liquid crystal, and isotropic liquid—nematic liquid crystal region in the order of descending temperature. The system is thermoreversible. Pattern formation in the 60% E7 film has been pursued by optical microscopy. The kinetics of the thermally quenched phase decomposition of the PDLC films were studied by time resolved light scattering. Several temperature quenches were carried out on the 40 % E7 content PDLC from an isotropic state (90 °C) to 25-45 °C. The time evolution of structure factor was analyzed in the context of non—linear theories to elucidate the mechanisms of mesophase transition and phase separation.