Effect of polymer matrix glass transition temperature on polymer dispersed liquid crystal electro-optics

Abstract

We have studied the electro‐optic properties as a function of temperature of a polymer dispersed liquid crystal film composed of E7 dispersed as droplets in a polyvinylformal (PVFM) matrix. The drive voltage and turn‐off time change abruptly as the temperature is raised above the glass transition temperature (T_g) of the PVFM matrix. There is essentially no hysteresis below, but significant hysteresis above T_g. These temperature effects are completely reversible. The rapid change in electro‐optic properties cannot be entirely explained by changes in the polymer dielectric properties or droplet shape. Freedericksz measurements show no abrupt change in the surface anchoring energy at T_g, which may be responsible for the changes observed in the electro‐optic response.