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We explore flexoelectro-optic effect in polymer stabilized cholesteric liquid crystals (CLC) with uniform lying helix texture. A method to enlarge the flexoelectric response of the CLC mixture is demonstrated by mixing two nematic liquid crystal host materials with large and small effective flexoelastic coefficients. By a choice of material composition of CLC mixture, a large angle of flexoelectrically driven in-plane rotation of helical axis with a submillisecond response time is obtained. Our findings will be useful for material design of future CLC mixtures for applications in flexoelectro-optic displays. [ABSTRACT FROM AUTHOR]

Presents a study that captured the director-field of a nematic liquid crystal droplet by a polymer network. Formation of anisotropic polymer network; Function of the glycerin matrix; Use of lecithin dopant to promote homeotropic surface anchoring.

Presents a study which analyzed the use of the nuclear-magnetic-resonance technique to liquid-crystal-dispersed-polymer systems. Details on the experiment; Results of the study; Conclusions.

Reveals that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers. Description of the liquid crystal used in the experiment; Data on the angular dependence of the reflection using the spectroscan meter.

Optical microscopic and the electric polarization studies show that amphiphilic glycolipids form tilted supramolecular structures in straight-core tilted smectic liquid crystals. Glycolipid and chiral smectic C (SmC) structures show spontaneous polarization while glycolipid and non-chiral SmC structures show no spontaneous polarization. We deduce from these observations that glycolipid molecules in chiral SmC structures nano-segregate in tilted double layers sandwiched between layers of straight-core liquid crystal molecules. In non-chiral SmC structures, tilted glycolipid molecules are nano-segregated in the layers of straight-core liquid crystal molecules. This indicates that, in contrast to the currently accepted interdigitated model, amphiphilic glycolipids may already have a tilted structure. [ABSTRACT FROM AUTHOR]

We have designed, synthesized, and evaluated the physical properties of some high birefringence (Deltan) isothiocyanato phenyltolane and quaterphenyl liquid crystals. These compounds exhibit Deltan~0.48-0.52 at room temperature and wavelength lambda=633 nm. Laterally substituted short alkyl chains and fluorine atom eliminate smectic phase and lower the melting temperature. The moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. These compounds can be used as dopants for color-sequential liquid crystal displays or eutectic mixtures for laser beam steering [ABSTRACT FROM PUBLISHER]

This paper describes the synthesis and mesomorphic properties of a SmC*-forming liquid crystalline compound with potential display applications. This compound with two fluorines in the 3,3'-positions of the terphenyl core and mixed unsaturated alkoxy/ester terminal groups is synthesized in an attempt to obtain a liquid crystal with ferroelectric properties useful for display applications. [ABSTRACT FROM AUTHOR]

Several compounds with high birefringence and having tolane structure were synthesized. For a high polarizability, isothiocyanato (NCS) terminal group was introduced. Another goal of this study was reduction of melting point and smectic phases by introduction of fluorine as lateral substituent. The transition temperatures for all the synthesized compounds and the refractive and dielectric indices for one of the compounds have been determined. Electro-optic (EO) measurements were also performed. [ABSTRACT FROM AUTHOR]

Polymer films possessing negative birefringence are used for the compensation of residual positive birefringence of liquid crystal displays in order to improve their viewing characteristics. We present several types of materials suitable for the fabrication of negative birefringence films and controllable distribution of optic axis. Films featuring a splayed optic axis can be made of discotic materials as a result of different anchoring forces acting at the film boundaries. Films with a planar optic axis can be made by shearing of thermotropic and lyotropic discotics and as a result of irradiation of photosensitive polymers with polarized light. Homeotropic alignment of optic axis can occur as a result of film shrinkage during solvent evaporation or photo-induced rotation of disk planes. [ABSTRACT FROM AUTHOR]

We report electro-optical studies of polymer-stabilized ferroelectric liquid crystals (PSFLCs). PSFLCs are made by photopolymerizing 3% reactive mesogenic monomer using the quasi bookshelf texture of a FLC as a template. We observe the formation of nano-scaled polymer fibrils templated by the two dimensionally ordered host. The polymer fibrils capture the orientation of the host; locate between smectic layers with thinner branches of the polymer fibrils interweaving the smectic layers. The polymer fibrils provide the additional surfaces, which facilitate the switching and shorten the response time of the PSFLCs. We also observe the V-shaped (threshold-less) switching behavior in PSFLCs. [ABSTRACT FROM AUTHOR]

We present novel scattering-type displays using antiferroelectric smectic phases of liquid crystals of bent-shaped molecules. There can be two distinct states ('racemic' and 'chiral') that work in opposite ways. The racemic structure is scattering in the OFF state and is optically clear under electric fields. The chiral structure is transparent at zero fields and is scattering in the field ON state. These two structures may be reversibly interchanged, implying their use in devices that consume energy only during switching from one stable state to the other. [ABSTRACT FROM AUTHOR]

In this work we study correlation between spatial molecular distributions in the contacting anisotropic polymer films and LC layers. Two kinds of side-chain azopolymers were employed: with the azochromophores containing hydrophobic OC 4 H 9 alkyl chain (P1) and strongly polar NO 2 group (P2) as the end substituences, respectively. The tilt orientation of azochromophores was induced by the oblique irradiation of the polymer films with non-polarized UV light. The tilt angle was controlled by the change of the angle of the UV light incidence. The uniform alignment of several LC with the quasilinear dependence of the LC pretilt angle on the inclination angle of azochromophores was observed for the films of P1. In contrast, the alignment of LCs on the films of P2 strongly depended on the structure of LC molecules and did not depend on the inclination of azochromophores in the polymer bulk. Possible reasons of the difference in results obtained for P1 and P2 are discussed. [ABSTRACT FROM AUTHOR]

Using polarized infrared (IR) spectroscopy we have observed deformation of a polymer network in a liquid crystal host during the reorientation of the liquid crystal by an external electric field. In the system studied, containing 2% BMBB-6 polymerized at zero applied field in the host nematic liquid crystal 6CB, the observed deformation angle was between 20[sup o] and 40[sup o] +/- 10[sup o]. These experimental results provide some of the first conclusive experimental evidence that the polymer network elastically deforms as a direct result of the reorientation of the liquid crystal host. [ABSTRACT FROM AUTHOR]

Internal polymer columnar structures in liquid crystal (LC) cells have been produced using the method of thermally-induced phase separation of LC/prepolymer solution and solidified by photopolymerization. These polymer columns adhere to both substrates and enhance control of the LC cell spacing and mechanical stability. The existence and profile of the polymer columns were investigated by optical and scanning electron microscopy techniques. Supertwisted nematic LC cells with polymer columnar structures have been constructed using this method and their electro-optical characteristics measured. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A liquid-crystal (LC) photoalignment method, based on the use of low-molecular-weight photo-cross-linkable (LMWPC) composites is proposed. The basic idea of this method is that cross linking or both cross linking and polymerization of LMWPC composites are realized immediately on the substrate simultaneously with the photoalignment or as a stage of the backing process. Providing the advantages of a conventional photoalignment method, the use of LMWPC composites simplifies the synthesis and alignment procedure, makes possible wide range control of pretilt angles, and enhances the thermal stability of the LC alignment. The abilities of this method are demonstrated using a series of cinnamate-containing monomers. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A switchable liquid crystal diffraction grating, responsive to both the frequency and magnitude of an applied voltage, is demonstrated. The grating is based on polymer stabilization of modulated states of the liquid crystal optic axis induced at frequencies near a sign inversion of the dielectric anisotropy. In a particular case of frequency-based switching, 70% of the transmitted intensity of a 633 nm laser beam can be shifted into or out of a ±12° forward arc by changing the frequency of an applied voltage between 10 and 16 kHz at a fixed amplitude of 27 V. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the polymer dispersion in low concentration with a cholesteric liquid crystal. Description of light modulators in the liquid crystal; Transparency state and irradiation of the cells; Creation of poly-focal conic domains for scattering; Transformation of liquid crystal into a homeotropic texture.

The combination of the transmission null ellipsometry and total absorption method, earlier approved for several polymer classes, is applied to study 3D orientational configurations of azochromophores in polymethacrylates with azobenzene side groups. The transformation of the initial orientation due to the photoexcitation of azochromophores is investigated. The dependence of the orientational configuration on the structure of azochromophore fragments and its concentration in the polymers are also studied. In the non-irradiated films, azochromofores strive to be aligned normally to the film plate. Under irradiation, if reorientation mechanism of the photoinduced ordering prevails, the azochromophores reorient perpendicularly to the polarization direction of the exciting light, E ex , and in the saturation state they are randomly distributed in the plane perpendicular to E ex . This implies that the induced structure is mainly influenced by the photoordering, while selfordering of polymer chains is not effective or overcome, presumably because of high T g of polymethacrylates. In case when photoselection ordering mechanism dominates, 3D distribution of azochromophores in the saturation state of irradiation is isotropic due to a strong exhaustion of the number of anisotropic trans isomers. The transient photoinduced orientations are biaxial independently on the dominating ordering mechanism. The reduction of the azochromophore's concentration in polymers reduces the anisotropy rate but not influence the trends described above. The observed regularities were earlier described for several other classes of photosensitive polymers and so they may be common rules for photoordering in the photochromic media. [ABSTRACT FROM AUTHOR]

We report a study of polymer network morphology in planar diffraction gratings formed from polymer-stabilized cholesteric liquid crystals. Photopolymerizing a mesogenic monomer yields a regular sawtooth morphology, composed of polymer sheets running at an acute angle between thick, uniformly aligned bundles which reside on the opposing substrates. To explain this morphology and evidence of two grating vectors in the diffraction pattern, we propose a model for the liquid-crystal director where out-of-phase twists at the surfaces gear into an interior twist, which has half the period of the surface twist, via splay distortions running between the substrates. The morphology also changes significantly when a nonmesogenic monomer is substituted or when selectively polarized states of UV radiation are used to cure the polymer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the use of a low concentration polymer network to stabilize electric field-induced diffraction gratings in cholesteric liquid crystals. The stabilized gratings can be electrically switched between a zero-field “on” state, which exhibits approximately 75% diffraction efficiency, and a moderate field (typically 3 V/μm) “off” state. Grating spacings between 1.7 and 30 μm are obtained in a 10 μm thick cell by variation of the concentration of chiral dopant used to form the cholesteric liquid crystal. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Any polar-ordered material with a spatially uniform polarization field is internally frustrated: The symmetry-required local preference for polarization is to be nonuniform, i.e., to be locally bouquet-like or "splayed." However, it is impossible to achieve splay of a preferred sign everywhere in space unless appropriate defects are introduced into the field. Typically, in materials like ferroelectric crystals or liquid crystals, such defects are not thermally stable, so that the local preference is globally frustrated and the polarization field remains uniform. Here, we report a class of fluid polar smectic liquid crystals in which local splay prevails in the form of periodic supermolecular-scale polarization modulation stripes coupled to layer undulation waves. The polar domains are locally chiral, and organized into patterns of alternating handedness and polarity; The fluid-layer undulations enable an extraordinary menagerie of filament and planar structures that identify such phases. [ABSTRACT FROM AUTHOR]