Dependence of the electro-optical properties of polymer dispersed liquid crystals on the photopolymerization process
We have studied the dependence of the electro-optical properties of polymer dispersed liquid crystals (PDLC) on the ultraviolet (UV) cure of the solution of monomer and liquid crystal. The kinetics of UV polymerization and its effect on the morphology of the phase separated droplets of liquid crystal determine the switching voltage, response time, and luminance of the PDLC. Using a series of statistically designed experiments, we have mapped the dependence of these responses on the weight fraction of liquid crystal, the temperature of the cell during cure, and light intensity. Temperature and composition are strongly coupled parameters that influence switching voltage, luminance, and response times. Switching voltages are minimized at 4–5 V for an 8 μm cell gap over a large region of temperature-composition space. An abrupt transition line occurs through that space. On one side of the transition line, voltage increases linearly either as temperature increases or composition decreases, and on the other sid...
Field controlled light scattering from nematic microdroplets
The light scattering and electro‐optic response of new material with display potential are investigated. The materials consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization. Droplet size, spacing, and distribution are readily controlled in these materials to allow optimization of displays based upon electrically controlled light scattering from the liquid crystal droplets. Preliminary experimental and theoretical studies of the light scattering properties show these materials to offer new features suitable for many display applications.
New display based on electrically induced index‐matching in an inhomogeneous medium
The operation of a new light modulation device that employs electric field controlled light scattering in an inhomogeneous medium is described. The orientation of a nematic liquid crystal, contained in micrometer sized inclusions in a nonabsorbing solid, is changed to produce a varying refractive index. When the refractive index of the liquid crystal matches that of the solid, the composite medium is nonscattering and transparent. If the refractive indices do not match, the medium is scattering and opaque. High contrast ratios have been measured for transmitted light with a response time of a ∼1 ms. The application of this technique to passive display devices is discussed.