ELECTROOPTIC PROPERTIES OF A POLYMER-DISPERSED LIQUID-CRYSTAL FILM - TEMPERATURE-DEPENDENCE AND PHASE-BEHAVIOR

Electro-optic measurements and optical microscopy were used in an inve stigation 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 th e applicability of a previously published formula for the switching vo ltage [Liq. Cryst. 5, 1453 (1989); 5, 1467 (1989)]. This formula is de rived from a model that requires droplet asphericity to be the dominan t factor determining the switching voltage, and strong anchoring of th e liquid crystal texture at the droplet walls. For a commonly studied PDLC film, the formula was found not to be applicable, presumably beca use of a loss of the strong anchoring boundary condition at the drople t walls, especially at elevated temperatures. Also, a structural trans ition within droplets of the PDLC film was observed. This transition g ives rise to dramatic changes in electro-optic behavior.