Electrooptical properties of gel-glass dispersed liquid crystals

Liquid crystal microdroplets can be trapped into silica gel-glasses by sol-gel processes. Several silica matrices containing different non-reacting organic radicals have been employed for preparing gel-glass dispersed liquid crystals (GDLC). The optical properties of thin GDLC layers may be modified by coating the material with transparent electrodes and applying external AC-voltage signals. Switching between opaque and transparent states is achieved. The sample transmission depends on the scattering properties of the material; no polarizers are required. The transmission of the transparent state is improved by matching the refractive indices of the gel-glass matrix and the liquid crystal. This can be achieved by adding high refractive index dopants to the starting mixture, or by substituting the non-reacting organic group of the silica matrix. Both approaches have been tested. Phenyl and methyl monomers have been used as well as titanium-based dopants. The resulting GDLC materials have been optimized by controlling the starting mixture composition, the reaction conditions, and the film preparation. The optics, dynamics, and stability of GDLC films are analyzed.