Polymer-Dispersed Liquid Crystals: Compositional Dependence of Structure and Morphology

Abstract

We have investigated the structure and morphology of polymer-dispersed liquid crystals (PDLCs). These materials are commonly prepared by UV-induced crosslinking of a compatible mixture of a prepolymer with a liquid-crystal (LC) eutectic and are of high interest for flat-panel display applications. We have found that the morphology of these materials varies greatly with UV-irradiation temperature and composition. Within a range of ca. 20-70 wt.% LC, lower-irradiation temperatures and higher LC contents favor a two-phase dispersion of bipolar droplets within the polymeric matrix. At low LC contents and high irradiation temperatures a new, space-filling spherulitic morphology is seen. These spherulites have a tangential orientation of the nematic LC molecules and are characterized by a highly unusual radial proliferation of surface inversion walls. We have found these defects to be initiated consistently at s=+l/2 disclinations and to be terminated at s=-l/2. The spherulites as well as the disclinations survive heating above the nematic-isotropic transition with little change.