Showing papers on "Liquid crystal published in 1983"

Constitutive Equation for Nematic Liquid Crystals under Weak Velocity Gradient Derived from a Molecular Kinetic Equation

Abstract: Constitutive equation for the nematic liquid crystals under weak velocity gradient is derived from the kinetic equation presented by Doi. The constitutive equation is consistent with the phenomenological equation proposed by Ericksen and Leslie. The six viscosity parameters (Leslie coefficients) appearing in the phenomenological theory are expressed by the molecular parameters.

Observation of macroscopic collective behavior and new texture in magnetically-doped liquid crystals

Abstract: The observation of macroscopic collective behavior in a nematic liquid crystal doped with magnetic grains is reported. This behavior is manifested as a uniform molecular orientational distortion of the entire matrix upon the application of external magnetic fields as low as <1 G. The dependence of the distortion on field strength, dopant concentration, and sample thickness is presented, and a theory which quantitatively accounts for the results is given. At high field intensities, the doped nematic exhibits a heretofore unreported texture of complex cellular topology.

Ferroelectric Liquid Crystal Electro-Optics Using the Surface Stabilized Structure

Abstract: The strong linear coupling of the director ň to electric field E in ferroelectric liquid crystals can be utilized to perform high-speed electro-optic switching suitable for device applications. In this article we summarize the current understanding of the high-speed, bistable, threshold-sensitive electro-optic effects obtained in planar structures using surface interactions to suppress the spontaneous director helix characteristic of the bulk ferroelectric liquid crystal.

Induction of the cholesteric mesophase in nematic liquid crystals: mechanism and application to the determination of bridged biaryl configurations

Abstract: On montre que quand une molecule «hote» chirale est dissoute dans un solvant nematique la chiralite est transferee au solvant. Un mecanisme d'induction de la phase cholesterique est deduit de l'orientation des molecules du solute determine par dichroisme lineaire et a partir des effets de solvant

Anisotropic aggregates of amphiphilic molecules in lyotropic nematic phases

Abstract: Les phases lyotropes nematiques de composes amphiphiles sont des solutions fluides d'agregats micellaires anisotropes. Les etudes par diffusion de neutrons completent les etudes aux rayons X et permettent de determiner la forme et les dimensions des agregats. Cas des systemes formes par le laurylsulfate de sodium, ou le laurate de potassium ― le decanol-1 et l'eau

Field-Induced First-Order Orientation Transitions in Ferroelectric Liquid Crystals

Abstract: Two new effects specific to ferroelectric liquid crystals are described: (a) ferroelectric polar surface interactions and (2) spontaneous splay of the polarization. It is shown that a consequence of these effects is the possibility of first-order reorientation transitions induced by applied electric fields.

Surface Anchoring of Liquid Crystal Molecules on Various Substrates

Abstract: Ever since Mauguin described the fabrication of liquid crystal cells by rubbing glass plates with paper to obtain uniform homogeneous alignment, scientists have been attempting to study and understand the mechanism of anchoring and the subsequent alignment of these materials on various substrates. More than 35 different methods for creating surface alignment have been reported using both organic and inorganic films as well as various mechanical treatments. In this paper, many of these methods are reviewed and categorized. The mechanism of surface anchoring involves not one but several mechanisms. The nature of the surface material, the liquid crystal structure, and the past history of the surface, all play major roles in determining the mechanism for a specific technique.

Liquid crystalline polymers with disc-like mesogens

Abstract: Resultats preliminaires sur les polysiloxanes discotiques avec des cycles triphenylene pentasubstitue fixes au squelette par des liaisons flexibles

Optically induced Freedericksz transition and bistability in a nematic liquid crystal

Abstract: An Euler equation, consistent with Maxwell's equations, for describing the optically induced spatial reorientation of the director of a homeotropically oriented nematic liquid crystal is obtained for the case of normal incidence. The exact solution describing the orientation of the director is obtained. By examining the maximum deformation angle near the threshold, the threshold intensity and the criterion for the physical parameters that indicate whether the transition is first- or second-order at the threshold are obtained. The hysteresis accompanying the first-order Freedericksz transition is discussed. By choosing a compound (PAA, $p$-azoxyanisole) with suitable material parameters from known nematic liquid crystals, an experiment is proposed to observe, for the first time, a first-order Freedericksz transition in nematic liquid crystals. The Zel'dovich approach [Sov. Phys.-JETP 54, 32 (1981)] based on the geometrical-optics approximation is shown to be internally inconsistent and also inconsistent with the geometrical-optics approximation. The Euler equation using a self-consistent geometrical-optics approximation is also obtained, and turns out to be identical to our exact Euler equation, but different from the infinite-plane-wave approximation used by Durbin et al. [Phys. Rev. Lett. 47, 1411 (1981)]. Detailed comparisons between our approach and the Durbin approach are made. The dynamics of the transition are discussed and an approximate solution is given. The transient responses to the laser switch-on and switch-off are shown to have exponential time dependence. Finally, the effects of surface interactions on the transition are discussed and the exact solution is given. The procedure for determining the threshold, the saturation, and the parallel-state-maintenance intensities is given. We also discuss the first-order transition and propose experimental methods manifesting the effects of surface interaction. The criterion for the transition to be first order at any intensity is given.

Orientation development in thermotropic liquid crystal polymers

Abstract: Thermotropic liquid crystal polymers are a new class of polymeric materials that consist of rigid backbone molecules and thus, even in the quiescent condition, take extended chain conformation to form optically anisotropic melts A systematic investigation was carried out on how this type of material responds to two basic flow fields: shear and elongation Rheological properties of the polymer in these flow fields have also been measured It was found that a high level of molecular orientation was readily obtained by elongational flow but not with shear flow Specifically, extraordinarily high orientation was obtained when the melt was subjected to small elongational strains, whiel shear strain or shear rate had little effect A possible mechanism to explain these behaviors is illustrated based on the existing observations or theories of rodlike molecules This finding was used to interpret the orientation distribution in the extruded and injection-molded articles

Discotic Mesophases of the Metal-Free Derivative of Octa (Dodecyloxymethyl) Phthalocyanine

Abstract: The mesomorphic behavior of octa (dodecyloxymethyl) phthalocyanine was studied with DSC, optical microscopy, and X-ray diffraction. Two discotic mesophases were observed as a function of temperature. Their structure corresponds to the piling up of the flat molecules in columns which are laterally assembled according to a two-dimensional hexagonal lattice (D = 31.2 A). The repeat distance of the molecules along the columns was found to be of about 4.5 A. The low-temperature discotic phase showed an extra sharp reflection at 20.5 A, indicating a further ordering of the molecules.

The Influence of an External Electric Field on the Structure of Chiral Sm C∗ Liquid Crystal

Abstract: The mechanism of a field induced transition from helical Sm C∗ to Sm C structure in a DOBAMBC liquid crystal situated between two glass plates has been studied by optical methods. The important role of a regular system of twist disclination lines (dechiralization lines) in unwinding the helical structure by electric field has been revealed. A simplified model of ±2π twist disclination pairs is proposed which describes the unwinding of the Sm C∗ structure. Under the external electric field the pairs of ±2π twist disclinations move and annihilate each other and thus effectively unwind the helical structure of the sample. Critical fields for switching the helical Sm C∗ structure, as well as the unwound structure, are estimated.

Temperature behavior of the order-parameter invariants in the uniaxial and biaxial nematic phases of a lyotropic liquid crystal

Abstract: Conoscopic observations have been made on a mixture of potassium laurate, 1-decanol, and ${\mathrm{D}}_{2}$O in the discotic-uniaxial, biaxial, and cylindric-uniaxial nematic phases. The differences between the principal refractive indices have been measured, leading to a complete determination of the tensor order parameter in all the three phases. In the biaxial phase, the symmetric invariants of the order parameter are found to have a linear dependence on temperature, in good agreement with the prediction of the mean-field model.

Liquid crystal display element

Abstract: PURPOSE:To obtain a liquid crystal display element securing the reliability of a terminal part and providing also a flattened film capable of controlling a uniform thickness of a liquid crystal layer, by constructing the flattened film so as to cover a sealed zone but not to cover the terminal zone. CONSTITUTION:The liquid crystal display element is constituted of a glass substrate 101, a transparent electrode 102 consisting of tin oxide or ITO, an orientation layer 103 for orienting liquid crystal molecules, a liquid crystal layer 104, a sealing zone 105, and a color filter layer 106. Also, a flattened film 107 is provided in between the color filter 106 and the electrode 102. The flattened film 107 is constructed so as to cover the sealed zone but not to cover the terminal zone. Thus, reliability of the terminal zone is secured and a liquid crystal display element having a flattened film capable of controlling uniformly thickness of the liquid crystal layer is obtd.

Rapid starting, high-speed liquid crystal variable optical retarder

Abstract: A liquid crystal cell (100) includes a chiral additive in the liquid crystal material (106) to operate the cell as a rapid starting, high-speed variable optical retarder. The cell is fabricated so that the surface noncontacting directors (116 and 118) of the opposed surfaces of the director alignment layers (112 and 112') of the electrode structures (102 and 104) are tilt-biased in opposite directions. This surface contacting director configuration induces rapid surface noncontacting director (120a, 120b, 120c, 120d, 120e) relaxation without optical bounce when the cell is switched from the field aligned ("ON") state to the partly relaxed ("OFF") state. The chiral additive prevents an inactive cell from relaxing to the splayed topological state, thereby enabling switching operation without a warm-up delay and preventing the surface of the cell from having a mottled appearance when it remains unused.

Method for driving liquid crystal element employing ferroelectric liquid crystal

Abstract: A method for driving a liquid crystal element including a ferroelectric liquid crystal sandwiched between a pair of substrates having electrodes on their opposite surfaces is disclosed. A pulse voltage for defining the light transmitting state of the liquid crystal element is applied to the ferroelectric liquid crystal. Before and/or after the application of the pulse voltage, the ferroelectric liquid crystal is applied with a voltage signal which renders the average value of voltages applied to the ferroelectric liquid crystal equal to zero.

Determination of the anisotropic potential at the nematic liquid crystal-to-wall interface

Abstract: The integrated birefringence of a surfactant (C16H33NH2)‐aligned methoxybenzylidene butylaniline cell as a function of applied magnetic field (up to 100 kG) has been measured. The Oseen and Frank elastic continuum theory and a generalized torque balance equation at the interface have been utilized for the calculation to fit the measured data. A very good fit to the data was obtained using an anisotropic liquid crystal‐to‐wall interfacial potential of the form C cos2 θ+C4 cos4 θ for the calculation. It was found that C4/C=−0.38.

Injection molding of thermotropic liquid crystal polymers

Abstract: Thermotropic liquid crystal polymers consist of rod-like molecules and are often called “self reinforcing thermoplastics.” Their rheological behaviors as well as orientation development during processing are often very similar to those of short fiber-filled composites. Without reinforcement, the polymer shows superior mechanical properties to conventional glass fiber-reinforced engineering resins. The orientation distribution in the crosssection as well as flow patterns in the molded thermotropic polymers are clearly visible to the naked eye due to color differences. This makes it particularly convenient to study the orientation distribution as well as the flow patterns of packing, back flow, jetting, flow instabilities, and weld line formation in injection molding. This paper discusses physical properties of a typical ther motropic polymer and their relationship to mold filling process in the injection molding.

Driving method of optical modulating element

Abstract: PURPOSE:To enable a bistable state by applying selectively information signals to a signal electrode group in synchronization with a sacnning electrode then having a signal application period when the signals different from the previously applied information signals are applied prior to application of the information signals. CONSTITUTION:A liquid crystal molecular layer 12 is vertically oriented to the plane of glass and is sealed between glass base plates 11 and 11' which are coated with transparent electrodes. When a voltage of a specified threshold or above is impressed between the electrodes on the plates 11 and 11', the spiral structure of liquid crystal molecules 13 are unraveled and the orienting direction of the molecules 13 can be changed in such a way that all dipole moments 14 are directed toward the electric field. The molecules 13 have a slender shape and exhibit refractive anisotropy in the long axis direction and short axis direction thereof. Therefore if polarizers disposed in the positional relation of crossed nicols with each other are placed on the top and bottom of the glass surfaces, the liquid crystal optical modulating element of which the optical characteristic changes with the impressed polarity of the voltage. The optical modulating element has the advantages that the response speed is fast and that the orientation of the liquid crystal molecules has a bistable state.

Alignment of ferroelectric lcds

Abstract: The alignment of liquid crystal materials in cells utilized for devices is significantly enhanced through the use of materials such as polyamides, polyimides, nylons, and polyesters. This expedient for alignment of liquid crystal materials is useful for nematic and cholesteric liquid crystals, but finds particularly advantageous use for aligning smectic liquid crystals.

Liquid crystal display device having color filter triads

Abstract: A multi-color liquid crystal display includes liquid crystal micro-shutters which open and close color filters arranged as dots in a mosaic or stripe pattern. Fine and clear color image display and color graphic display are realized in the device wherein the filters are within the LCD panel, being formed on one substrate and covered by the driving electrode.