Electro-optic properties of a polymer-dispersed liquid-crystal film: Temperature dependence and phase behavior

Abstract

Electro-optic measurements and optical microscopy were used in an investigation into the microscopic properties that determine the switching characteristics of a polymer-dispersed liquid-crystal (PDLC) film. A simple test is demonstrated that provides a necessary condition for the applicability of a previously published formula for the switching voltage [Liq. Cryst. 5, 1453 (1989); 5, 1467 (1989)]. This formula is derived from a model that requires droplet asphericity to be the dominant factor determining the switching voltage, and strong anchoring of the liquid crystal texture at the droplet walls. For a commonly studied PDLC film, the formula was found not to be applicable, presumably because of a loss of the strong anchoring boundary condition at the droplet walls, especially at elevated temperatures. Also, a structural transition within droplets of the PDLC film was observed. This transition gives rise to dramatic changes in electro-optic behavior. \textcopyright{} 1996 The American Physical Society.