Foreword. Series Editor's Foreword. Preface. 1. Liquid crystal physics.* Introduction.* Thermodynamics and statistic physics.* Orientational order.* Elastic properties of liquid crystals.* Response of liquid crystals to electro-magnetic fields.* Anchoring effects of nematic liquid crystal at surfaces. 2. Propagation of light in anisotropic optical medium.* Electromagnetic wave.* Polarization.* Propagation of light in uniform anisotropic optical media.* Propagation of light in cholesteric liquid crystals. 3. Optical modeling methods.* Jones matrix method.* Mueller matrix method.* Berreman 4x4 method. 4. Effects of Electric field on Liquid Crystals.* Dielectric interaction.* Flexoelectric Effect.* Ferroelectricity in liquid crystals. 5. Freedericksz transition.* Calculus of variation.* The Fredeericksz transition: statics.* The Freedericksz transition: dynamics. 6. Liquid Crystal Materials.* Introduction.* Refractive indices.* Dielectric constants.* Rotational Viscosity.* Elastic constant.* Figure-of-merits.* Refractive index matching between liquid crystals and polymers. 7. Modeling of liquid crystal director configuration.* Electric energy of liquid crystals.* Modeling electric field.* Simulation of liquid crystal director configuration. 8. Transmissive liquid crystal display.* Introduction.* Twisted nematic cells.* In plane switching (IPS) mode.* Vertical alignment (VA) mode.* Multi-domain Vertical Alignment (MVA) Cells.* Optically compensated bend (OCB) cell. 9. Reflective and Trasreflective display.* Introduction.* Reflective liquid crystal displays.* Transflector.* Classification of Transflective LCDs.* Dual-cell-gap Transflective LCDs.* Single-cell-gap Transflective LCDs.* Performance of transflective LCDs. 10. Liquid crystal display matrices, drive schemes and bistable displays.* Segmented displays.* Passive matrix displays and drive scheme.* Active Matrix Displays.* Bistable ferroelectric liquid crystal displays and drive scheme.* Bistable nematic displays.* Bistable cholesteric reflective display. 11. Liquid crystal/polymer composites. * Introduction.* Phase separation.* Scattering properties of liquid crystal/polymer composites.* Polymer dispersed liquid crystals.* Polymer stabilization liquid crystals.* Displays from liquid crystal/polymer composites. 12. Tunable liquid crystal photonic devices. * Introduction.* Laser beam steering.* Variable Optical Attenuators.* Tunable-Focus Lens.* Polarization-Independent LC Devices. Index.

Fundamentals of Liquid Crystal Devices

▪ Abstract The formation of switchable holographic gratings from polymer-dispersed liquid crystals (H-PDLCs) allows for the development of switchable transmissive and reflective diffractive optics. These structures are created by the coherent interference of laser radiation within a syrup containing photoreactive monomer, initiator, and liquid crystal. Local differences in photopolymerization rates induce phase separation of discrete LC domains to occur periodically commensurate with the period of the interference pattern. These spatially periodic gratings of nano-scale sized LC domains can be formed on grating length scales ranging from 100 nm to microns depending on the optics of fabrication. True Bragg gratings are formed with spacings typically less than 1 μm. Owing to the refractive profile generated by this periodic two-phase structure, diffraction of light occurs. Electrical switching of the average director orientation within the LC domains results in a modulation of diffracted radiation. This tec...

Holographic Polymer-Dispersed Liquid Crystals (H-PDLCs)1

Polymer as an important component of blends and composites with liquid crystals

Polymer-dispersed liquid crystals (PDLC) are widely used for electro-optic applications such as flexible displays, privacy windows or projection displays. Besides these applications, the confinement of a liquid crystal to small cavities is of fundamental interest. The present paper contains a review of the work on nematic and cholesteric PDLCs. Moreover, some very recent developments are summarized such as the use of ferroelectric liquid crystals for PDLC applications.

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Polymer-dispersed liquid crystals From the nematic curvilinear aligned phase to ferroelectric films

Holographic reflection gratings in polymer-dispersed liquid crystals (H-PDLCs) were formed by thiol−ene photopolymerization. Using UV laser light and a single prism, electrically switchable reflection gratings in blue, green, yellow, and red colors were fabricated. Results indicate that thiol−ene polymers function as better hosts for H-PDLC than multifunctional acrylate as matrixes. These differences are the result of a much different temporal structure development caused by fundamental differences in the polymerization propagation mechanism:  a step-growth addition mechanism for the thiol−ene system compared to a chain-growth addition mechanism in multifunctional acrylates. Morphology studies by TEM support these conclusions, as striking differences in droplet shape and uniformity are observed. Discrete nematic droplets with a nearly spherical shape were seen. Thiol−ene polymers offer lower switching fields, higher diffraction efficiencies, better optical properties, and higher thermal stabilities. The r...

Switchable Holographic Polymer-Dispersed Liquid Crystal Reflection Gratings Based on Thiol−Ene Photopolymerization

The response times and operating voltages of light shutters formed from polymer dispersed liquid crystals (PDLCs) have been studied experimentally and the results compared with calculations based on non-sperhically shaped nematic droplet models. The experiments were performed on light shutters with elongated and uniformly aligned droplets where the relaxation time and voltage response were measured. It is shown that the droplet shape can be a dominant factor, particularly for the relaxation time, and the data are compared with equations derived in terms of the aspect ratio of the droplet l = a/b, where a and b are the lengths of the semi-major and semi-minor axes, respectively, of the elongated droplet. It is further demonstrated that the electric field inside the droplet can be considerably smaller than the applied field, due to the conductivity and dielectric properties of the polymer and liquid crystal materials. These data are used to obtain values for the ratio of the conductivities of the p...

Response times and voltages for PDLC light shutters

Computer simulations are made of polarizing microscope textures of supramicron‐sized nematic droplets with director configurations which commonly occur in polymer and other dispersions. The simulations are computed from polarization rotations and phase shifts caused by nonuniform optical anisotropies of the nematic structure in liquid crystal droplets. The treatment is limited to the case of spherical droplets which are optically soft so that reflection and refraction at the droplet surface, as well as refraction on any internal structure, can be neglected. Simulated polarizing microscope textures of four different director configurations at different orientations are presented graphically. The simulated pictures are shown to compare well with observations of actual nematic droplets viewed under crossed polars.

Microscope textures of nematic droplets in polymer dispersed liquid crystals

A Commentary on the paper ”Response times and voltages for PDLC shutters„, by Bao‐Gang Wu, John H. Erdman and J. William Doane. First published in Liquid Crystals, 5, 1453‐1465 (1989).

John H. Erdmann

Papers

Response times and voltages for PDLC light shutters

Microscope textures of nematic droplets in polymer dispersed liquid crystals

PDLC shutters: where has this technology gone?