Polymer Dispersed Liquid Crystals Incorporating Isotropic Dyes

Colored polymer dispersed liquid crystal, PDLC, shutters are formed by the inclusion of isotropic dyes in the epoxy resin and liquid crystal used to make the shutter. Upon curing, the dye is dissolved in both the epoxy binder and the liquid crystal droplets. The shutters are highly colored and scattering in the absence of an aligning electric field, OFF state. Application of an electric field across the film aligns the director of the liquid crystal in the droplets, switching the shutter to a lightly colored, transparent, ON state. In the ON state, light passes through the film unscattered and its path length is essentially equal to the thickness of the cell. In the scattering, OFF, state the path length of light is increased due to Rayleigh-Gans and multiple scattering. The optical density, OD, of the shutter is directly proportional to the path length of the light. The shutter OD is measured in both the ON and OFF states using a LTV-visible spectrophotometer equipped with an integrating sphere and an undyed PDLC shutter used as a reference. The ratio of the OD in the OFF to the ON state is a direct measure of the scattering efficiency of the shutter. Using this ratio, it is possible to calculate the dye concentration that will maximize the change in percent transmission through the film between the ON and OFF states. High contrast, colored displays have been made using isotropic dye containing PDLC films and complementary colored backgrounds.