Light Scattering from Polymer-Dispersed Liquid Crystals.

Light-scattering apparatus was designed and constructed for studying polymer dispersed liquid crystals (PDLCs). Light -scattering and transmission measurements were made on these materials for two specific cases: the aligned configuration induced by an applied electric field and the radial configuration in broadly dispersed droplets. The results of these measurements were compared to the recent calculations of Zumer in the Rayleigh-Gans and anomalous diffraction regimes. Measurement of the total scattering cross section for the aligned configuration in samples with submicron droplets compares favorably with the theoretical calculations of Zumer's Rayleigh-Gans limit. Measurements of samples containing field-aligned and radially-configured supramicron droplets verify Zumer's anomalous diffraction predictions. Transmission studies of display quality samples with aligned submicron droplets indicate that there is a distribution of +/-10^circ about the applied-field direction in the droplet alignment. This distribution, presented even in a saturating field, is believed to be one of the contributing factors to the haze observed in the ON state of PDLC light shutters. We also present for the first time in this dissertation transmission measurements on PDLCs in which the polymer binder was replaced by an aligned polymer liquid crystal. We show that light scattered at wide angles of incidence is substantially reduced for the aligned droplet configuration (ON-state) in these samples. These materials allow wide -viewing angle liquid crystal displays and haze-free switchable windows. The high surface-to-volume ratio which exists in PDLC systems and the curved interface between the liquid crystal and solid polymer present a unique situation for studying the anchoring of liquid crystalline molecules. A transition from parallel to normal alignment was observed at the interface between the liquid crystal in the droplets and the polyurethane binder. We also report the observation of a double transition in the transmitted intensity near the N-I transition temperature of the liquid crystal confined to the droplets.