J. W. Doane

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.

Cholesteric Liquid-Crystal Polymer Dispersion for Haze-Free Light Shutters

A new dispersion involving a polymer in low concentration with a cholesteric liquid crystal is reported. Two types of light modulators from these materials are described as a normal mode shutter which is opaque (light scattering) in the field‐OFF state and transparent in the field‐ON state and a reverse‐mode shutter with the opposite field conditions. The transparent state of both cells is haze‐free for all viewing angles making the material attractive for window applications and direct view displays.

Control of Reflectivity and Bistability in Displays Using Cholesteric Liquid-Crystals

It is demonstrated that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers. Dispersing a polymer in the liquid crystal or using a cell with an inhomogeneous surface anchoring creates permanent defects which result in long‐term bistability, high contrast at large viewing angles, and gray scale. The wide‐angle, reflective feature makes cholesteric materials suitable for displays without backlights and bistability provides flicker‐free operation.

Polymer networks formed in liquid crystals

Abstract Monomers with reactive double bonds were mixed with liquid crystals and polymerized under UV irradiation. The polymer networks formed are anisotropic and consist of fibrils. The orientation of the polymer networks depend on the orientation of the liquid crystals during polymerization. Optical and scanning electron microscopy (SEM) were used to study the polymer networks.

Nematic director orientation in a liquid‐crystal‐dispersed polymer: A deuterium nuclear‐magnetic‐resonance approach

The nuclear‐magnetic‐resonance (NMR) technique is employed to liquid‐crystal‐dispersed‐polymer (LCDP) systems. Deuterium NMR is used to determine director distributions in LCDP cells in the presence of a magnetic field. The samples consist of a nematic liquid crystal mixed with small percentages of a monomer that is polymerized under different conditions after dissolving it in the liquid crystal. NMR spectra of the deuterated liquid‐crystal molecules give information on orientation and order in such systems. The orientation of the polymer skeleton formed during the polymerization is found to be stable. It determines the orientation of the nematic director even in the presence of a strong external magnetic field. Simple models for the director field are presented.

Light extinction in a dispersion of small nematic droplets

A study is made of the light-transmission properties of materials in which submicrometer-sized nematic droplets are dispersed in a solid polymeric matrix. Theoretical evaluations of the differential and total cross sections for droplets with different nematic configurations are performed in the Rayleigh–Gans approximation. The corresponding attenuation coefficients are calculated in a single-scattering approximation in which the effect of interdroplet interference is taken into account. The spatial distribution of the droplets is introduced by means of a pair-correlation function. Theoretical calculations are in excellent agreement with experimental data obtained from thin films of materials consisting of cyanobiphenyl droplets dispersed in an epoxy resin.

Molecular Orientational Order and NMR in the Uniaxial and Biaxial Phases

Abstract Although of fundamental interest, orientational order is a property of the liquid crystalline phases which has not been well etermined. Only that order which is described by teh parameter S = = has been given intesive study. there are other useful order parameters. This paper discusses some of those parameters and their measurement. Like S =, the parameters described come from the transformation properties of the speherical harmonics of order two. In the uniaxial phases a parameter which describes the asymmetry in the order of the molecular long axis is discussed and a measurement of its temperature dependence presented. The technique uaed in the measurement is deuteron magnetic resonance and the compoundis selectively deuterated n-heptyloxyazoxybenzene (HOAB). In addition the conformation of the melecule and its temperature dependence throughout the liquid crystalline phase is discussed. The order parameter concept is extended to the biaxial phases where the influence of some of t...

Proton spin–lattice relaxation in nematic microdroplets

The frequency and temperature dependences of the proton spin–lattice relaxation rate have been studied in nematic droplets embedded in a solid polymer matrix. The comparison of these data to those for bulk nematic and pure polymer samples shows that cross‐relaxation between liquid crystal and polymer protons dominates the liquid crystal relaxation in the MHz frequency region, while at low frequencies the translationally induced molecular rotation becomes important. The cross‐relaxation rate is found to be ≈103 s−1 giving an order of magnitude estimate 10−4–10−3 s for the time for which a liquid crystal molecule is bonded to the surface.

Electrooptic properties of polymer dispersed liquid crystals

Abstract An investigation of the electrooptic properties of polymer dispersed liquid crystals (PDLC) is presented. These materials are light modulating systems. They show a reversible optical response from an opaque state to a highly transmitting state under the action of an appropriate electric field which aligns the liquid crystal director. The switching voltage required to establish such an electric field has been monitored as a function of (i) the starting materials used for the preparation of the PDLCs, (ii) the ageing (curing time) of the PDLC cells. Other physical properties, such as the electrical resistivity and the dielectric constant of the materials, have been measured. The correlations between these properties have been studied. The PDLC switching voltage appears to be strongly correlated with the resistivity. Our data suggest that ionic impurities play a dominant role with respect to the electrooptic response of PDLC films.

Characterization of reflective cholesteric liquid‐crystal displays

We report on the optical reflective properties of the planar texture of cholesteric liquid crystal reflective displays. The reflecting liquid‐crystal medium is partitioned into many distinguishable domains, each of which is characterized by its local dielectric anisotropy. Such a multidomain cholesteric liquid crystal is made bistable by either dispersing a low concentration of polymer or by treating the cell substrate surfaces, both of which affect the domain alignment. Both types of cells result in a bistable colorful reflective display. We determine the role that the polymer network and surface alignment has on the reflective properties in regard to their photometric and colorimetric properties as a function of viewing angle using both collimated and diffuse illumination. Both the polymer network and surface anchoring have the effect of distributing the orientation of the cholesteric helix axes about the cell normal. Theoretically we characterize these cells by this distribution. Our goal is to properl...