Electro-optic and phase transition studies on polymer dispersed liquid crystal films

ABSTRACT We obtained polymer dispersed liquid crystal (PDLC) films using a nematic liquid crystal E7 and polymethyl methacrylate(50% by weight) by the Solvent Induced Phase Separation method. Using the Thermally Stimulated Depolarization Currentmethod we determined the clearing point of the pure liquid crystal and of the PDLC films. The glass transition temperatureof the PMMA matrix has also been determined. The results have been compared with those obtained by DifferentialScanning Calorimetry. During the TSDC measurements we registered the optical transmission as a function of temperature,thus the thermal switch operation being demonstrated.Keywords: liquid crystal, polymer dispersed liquid crystal, phase transition, thennally stimulated depolarization currents 1. INTRODUCTION Polymer dispersed liquid crystal (PDLC) composite materials consist of micrometer sized liquid crystal (LC) dropletsembedded in a solid polymer matrix1 . There are two different types of such materials: a. Plastic materials with open orconnected micropores which can be filled with a nematic liquid crystal. b. Materials containing encapsulated liquid crystals,