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...
Molecular alignment of rigid rods in nonrigid spherical pores.
We have investigated the orientation ordering of two shish-kebab chains confined by spherically harmonic potentials through Monte Carlo simulations and asymptotic analysis. The rigid rod is modeled as shish-kebab chains consisting of tangent hard spheres aligned in the same axis, and the harmonic potential is chosen to model nonrigid cavities. We first show that the interactions between a rod and the spherically harmonic potential are independent of chain orientation, indicating that the alignment of two confined rods arises from the excluded volume interactions alone. In the strong fields, the order parameter of two confined rods converges to different values, depending on the parity of chain length. From asymptotic order parameters, we find that the rods of odd-number beads rotate more freely even under the limiting strong confinement. However, the two rods of even-number beads are essentially trapped in a configuration of perpendicular alignment through intercalation of their central grooves. We attribute the dependence of the parity of chain length to the different locations of the center-of-mass in a rod for these two cases. Furthermore, we compare the shish-kebab chains with different rod models in the simulations, and utilize these models to explore the effect of the local rod smoothness on molecular alignment. Our findings suggest that increasing local rod smoothness enhances the rotational degree of freedom for confined rods, and the effect of local rod roughness emerges under strong enough applied potentials.
Reverse-mode microdroplet liquid crystal display
This paper presents the production of the a reverse-mode microdroplet liquid crystal (RMLC) light shutter display. In this unit, the display is formed by a thin polymer film with dispersed liquid crystal microdroplets. The display is light transmissive in the absence of an applied electrical field. The display is converted to a non-transmissive state (i.e. absorbing or scattering) when an electrical field is applied. The "off' and "on" state. of this display are thus exactly opposite to that encountered in "normal-mode" microdroplet liquid crystal display devices such as polymer dispersed liquid crystals (PDLC)15 or Nematic Curvilinear Aligned Phase (NCAP)6. The Reverse Mode Microdroplet Liquid Crystal is obtained by modification of the surface energy of the polymer which encases liquid crystals via reaction of a dopant incorporated inside of the microdroplet during the droplet formation within the inside polymer layer. The liquid crystal used in RMLC is of negative dielectric anisotropy.