Showing papers on "Liquid crystal published in 1973"
TL;DR: In this paper, the structural significance of platelets which occur in the blue phase is considered. And the authors show that a blue phase occurs for each derivative at the amorphous liquid-cholesteric liquid crystal transition.
1,043 citations
TL;DR: New organic compounds of positive dielectric anisotropy giving nematic liquid crystals at room temperature, either as the pure compounds or in admixture, are described in this article, where they are of improved stability, and function well in electro-optical devices based on the twisted-nematic or cholesteric nematic phase-change effects.
Abstract: New organic compounds of positive dielectric anisotropy giving nematic liquid crystals at room temperature, either as the pure compounds or in admixture, are described. These materials are of improved stability, and function well in electro-optical devices based on the twisted-nematic or cholesteric-nematic phase-change effects.
411 citations
TL;DR: In this article, a truncated power series was used to approximate the variation of optical parameters through each layer and two ways to obtain fast convergence of numerical computations with layers of homogeneous anisotropic material that are several wavelengths thick.
Abstract: Optical transmittance and reflectance of continuously varying anisotropic planar media, such as nematic liquid crystals in Schadt–Helfrich twist cells or cholesterics between parallel rubbed surfaces, have previously been computed with a 4 × 4 matrix method by considering the medium as broken up into many thin parallel layers and treating each as if it had homogeneous anisotropic optical parameters. A matrix multiplication was done for each layer, and unless each layer was much less than one wavelength thick, several more multiplications were done within each layer. Here we show how to do numerical computations with equal accuracy using much thicker layers. We use a truncated power series to approximate the variation of optical parameters through each layer. We also show two ways to obtain fast convergence of numerical computations with layers of homogeneous anisotropic material that are several wavelengths thick. We use the method to get a better understanding of the optical properties of twist cells, particularly for oblique rays. The possibility of measuring elastic constants by comparing measured with computed transmittance of twist cells is suggested.
256 citations
TL;DR: In this article, the authors discuss the nature of the order in the main smectic phases (A, C, and B) together with the related phase transitions, and suggest that the B phase may correspond to a plastic crystal, or to a system of weakly coupled solid layers: to discriminate between these two models, acoustical studies using shear waves appear to be most promising.
Abstract: We discuss the nature of the order in the main smectic phases (A, C, and B) together with the related phase transitions. (1) The B phase may correspond to a plastic crystal, or to a system of weakly coupled solid layers: to discriminate between these two models, acoustical studies using shear waves appear to be most promising, (2) the transitions A N, C N, C A (where N stands for nematic) may be of second order in certain cases, which will allow for a number of interesting experiments. The C A transition should be very similar to the λ transition of helium, and some critical exponents which are not accessible in helium could be measured here. The N A transition is similar to the onset of superconductivity in a metal. A bend (or twist) deformation tends to suppress the A phase just as a magnetic field destroys superconductivity. In the N phase the twist and bend elastic constants should show pretransitional anomalies. The C N transition is more complex. A tentative calculation suggests...
244 citations
TL;DR: This article observed alignment of nematic, cholesteric and smectic liquid crystals in directions depending on the orientation of submicroscopic, parallel grooves in adjacent glass and fused quartz surfaces.
Abstract: We have observed alignment of nematic, cholesteric and smectic liquid crystals in directions depending on the orientation of submicroscopic, parallel grooves in adjacent glass and fused quartz surfaces. The alignment can be explained on the basis of elastic strain energy in the bulk of the liquid crystal that would be increased if the long axes of the molecules were aligned by the surface but were not approximately parallel to the groove direction. We have also observed alignment parallel to grooved surfaces but skewed with respect to the grooves, apparently when long molecules become attached to the surface in a direction that causes a competing torque on the director of adjacent liquid crystal molecules.
243 citations
TL;DR: In this paper, the stability of cylindrically symmetrical line disclinations is examined by continum theory calculations and topological arguments, to show that these singularities can almost always be replaced by a continuous structure of lower energy.
Abstract: The stability of cylindrically symmetrical line disclinations is examined by continum theory calculations and topological arguments, to show that these singularities can almost always be replaced by a continuous structure of lower energy. The calculations are applied to the four basic types of index ± 2 structures. Experimental observations are presented to support the proposed continuous structures as seen in cylindrical samples, and in the classical structures a fils and a noyaux.
235 citations
232 citations
TL;DR: In this paper, the dynamics of the distortion of a well-oriented nematic liquid crystal film in a perpendicular field around the Freedericks critical field value is studied both theoretically and experimentally.
Abstract: 2014 The dynamics of the distortion of a well-oriented nematic liquid crystal film in a perpendicular field around the Freedericks critical field value is studied both theoretically and experimentally. The experimental thermal and optical techniques have already been used for the description of the equilibrium properties of the transition. Their use for the measurement of transition rates leads to an accurate verification of the Leslie-Ericksen hydrodynamic theory and to a demonstration of the role of back flow effects. The divergence of the characteristic time close to the critical value follows accurately the general Landau model of second order phase transitions. The value of the twist viscosity coefficient 03B31 is obtained. LE JOURNAL DE PHYSIQUE TOME 34, JANVIER 1973,
197 citations
TL;DR: In this article, the decay function of the electric dipole polarization has been calculated in terms of the correlation function of Wigner rotation matrices, and the orientational potential energy function has been expanded as a series of Legendre polynomials.
Abstract: The dipole relaxation behaviour in liquid crystals as a function of the molecular ordering has been interpreted theoretically. The decay function of the electric dipole polarization has been calculated in terms of the correlation function of the Wigner rotation matrices. The orientational potential energy function has been expanded as a series of Legendre polynomials, and the contributions of the various terms investigated.
182 citations
TL;DR: The elastic constants of a hard-rod liquid crystal are calculated using the Onsager theory as discussed by the authors, with results similar to those given by Priest, and the elastic constants are shown to be tight.
Abstract: The elastic constants of a hard-rod liquid crystal are calculated using the Onsager theory, with results similar to those given by Priest.
179 citations
TL;DR: The role of surface topography and surface chemistry has been distinguished through the use of known surfactans, intentionally deformed substrates, and electron microscopy, and the roles of surface chemistry have been distinguished: substrates with surface energy lower than the liquid crystal surface tension cause homeotropic alignment; otherwise alignment is parallel to the substrate plane, following any long-range order.
Abstract: Chatelain hypothesized that orientation of liquid crystals by interaction with the substrate is due to an adsorbed layer of fatty contaminants, but substrate topography has also been postulated as a causal factor. Experiments with chemically cleaned surfaces rubbed without contamination now confirm the importance of the impurity layer, which has been investigated using Auger spectrometry. Through the use of known surfactans, intentionally deformed substrates, and electron microscopy, the roles of surface topography and surface chemistry have been distinguished: substrates with surface energy lower than the liquid crystal surface tension cause homeotropic alignment; otherwise alignment is parallel to the substrate plane, following any long-range order, e.g., grooves, present on the surface.
01 Jul 1973
TL;DR: In this paper, the surface-generated orienting forces acting on liquid crystals (LC's) result from physicochemical processes, eg, hydrogen bonding, Van der Waal's interactions, or dipolar interactions, and from mechanical interactions as a result of the LC's anisotropic elasticity.
Abstract: The surface-generated orienting forces acting on liquid crystals (LC's) result from physicochemical processes, eg, hydrogen bonding, Van der Waal's interactions, or dipolar interactions, and from mechanical interactions as a result of the LC's anisotropic elasticity For flat, untextured surfaces, the physicochemical processes prevail, while for textured surfaces, the anisotropic elastic interactions must also be considered These sometimes competing processes are compared quantitatively, and the various orienting techniques and materials are discussed It is shown that although both physicochemical and anisotropic elastic interactions are important, the former will typically predominate
TL;DR: In this article, the character of the nematicisotropic phase transition can be continuously changed from first to second order and a new biaxial liquid crystal phase can be obtained by mixing suitable platelike and rodlike molecules.
Abstract: Model calculations are presented which indicate that the character of the nematic‐isotropic phase transition can be continuously changed from first to second order and that a new biaxial liquid crystal phase can be obtained by mixing suitable platelike and rodlike molecules Precursors of the predicted behavior should be observable from trends in the concentration dependence of the transition temperature and the discontinuity in the order parameter
TL;DR: In this paper, the structure of spherical droplets of nematic and cholesteric materials floating in an isotropic liquid was experimentally investigated by microscopic observation with polarized light.
Abstract: The structure of spherical droplets of nematic and cholesteric materials floating in an isotropic liquid is experimentally investigated by microscopic observation with polarized light. In nematic droplets either a star configuration or a bipolar configuration have been observed depending on the nature of the isotropic liquid. Cholesteric droplets adopt a spiral shaped structure whenever the radius of the droplet is much larger than the helical pitch. Changes in optical patterns induced by a magnetic field are analysed.
TL;DR: The first practical application of smectic liquid crystals, an infrared-laser-addressed light valve for the recording, storage, and display of high-resolution graphic images, was described in this article.
Abstract: Thermally induced optical storage and erasure (local and nonlocal) of scattering centers in thin films of smectic liquid crystals has been demonstrated. These new thermo‐optic and electrothermo‐optic effects provide the basis for what is believed to be the first practical application of smectic liquid crystals, an infrared‐laser‐addressed light valve for the recording, storage, and display of high‐resolution graphic images.
Patent•
19 Nov 1973
TL;DR: In this paper, a rear view mirror assembly comprising a reflective surface, and a liquid crystal assembly covering the reflective surface is used for controlling the voltage output of the voltage source, which is applied to the coatings of conductive material.
Abstract: A rear view mirror assembly comprising a reflective surface, and a liquid crystal assembly covering the reflective surface The liquid crystal assembly comprises a thin layer of liquid nematic material sandwiched between rigid panes of transparent material, the rigid panes having a thin, transparent coating of conductive material thereon in uniform contact with the nematic material The nematic material has a quiescent transparent state with no voltage applied and a turbulent opaque state when voltage is applied with the opaqueness being directly related to the applied voltage A voltage source is supplied and a photocell or a similar light-responsive device is used for controlling the voltage output of the voltage source The controlled output of the voltage source is applied to the coatings of conductive material The photocell is effective, when light impinges thereon, to apply a voltage level to the nematic material
TL;DR: In this paper, the actual position of the system of liquid crystalline modifications is discussed, which is based on the relations of miscibility of the liquid crystal modifications and on their texture.
Abstract: We deal with the actual position of the system of liquid crystalline modifications. This system is based on the relations of miscibility of the liquid crystalline modifications and on their texture...
Patent•
18 Apr 1973
TL;DR: In this article, a matrix array of reflective electrodes, as well as the individual addressing circuitry (field effect transistor) and electrical storage circuitry (capacitor) for each cell of the display panel, are formed on semiconductor backplates such that each reflective electrode forms one element or plate of the capacitor for the corresponding cell.
Abstract: Liquid crystal display systems having display panels in which a matrix array of reflective electrodes, as well as the individual addressing circuitry (field effect transistor) and electrical storage circuitry (capacitor) for each cell of the display panel, are formed on semiconductor backplates such that each reflective electrode forms one element or plate of the capacitor for the corresponding cell. Each field effect transistor is utilized to address an associated element of the matrix array, and the associated storage capacitor maintains the applied potential across the liquid crystal cell for a period sufficient for scattering centers to be formed in the liquid crystal material.
TL;DR: In this paper, a liquid crystal material which at least contains a compound having a molecular structure such that the material exhibits a liquid-crystal phase, the molecular structure of the compound being selected from one of the following structures: the structure, a simple ortho-substituted derivative of the structure, and a derivative in which a simple bridging group is contained between two of the orthopositions of the said structure wherein X and Y are different parasubstituents of the kind which promote liquid crystal behaviour.
Abstract: OF THE DISCLOSURE A liquid crystal material which at least contains a compound having a molecular structure such that the material exhibits a liquid crystal phase, the molecular structure of the compound being selected from one of the following structures: the structure ; a simple ortho-substituted derivative of the structure ; and a derivative of the structure in which a simple bridging group is contained between two of the ortho-positions of the said structure wherein X and Y are different para-substituents of the kind which promote liquid crystal behaviour, the para-substituent X being a group selected from the following list: an alkoxy group having more than one carbon atom; an alkyl group; an acyloxy group; and an alkenyl group; and the para-substituent Y being selected from the following list: a cyano group; a benzene ring substituted in the para-position by a cyano group; and a plurality of directly para-linked benzene rings in which the end ring remote from the substituent X is substituted in the para-position by a cyano group. The material may be the said compound or it may be a multi-component solution or mixture containing it. The liquid crystal material may be nematic, smectic or cholesteric depending on the selection of the substituents X and Y. A device such as a twisted nematic effect device, incorporating the material may be operated at low temperatures. The material does not suffer from significant chemical and/or photochemical decomposition when used in a liquid crystal device.
TL;DR: In this article, it was shown that molecular ordering in the isotropic phase of MBBA can be induced by an intense laser field and the ordering relaxation time as a function of temperature.
Abstract: We have shown by measuring the field-induced refractive index that molecular ordering in the isotropic phase of $p$-methoxy benzylidene $p\ensuremath{-}n$-butylaniline (MBBA) can be induced by an intense laser field. We have also measured directly the ordering relaxation time as a function of temperature. The results are compared with the predictions of the Landau---de Gennes model.
TL;DR: In this article, nuclear magnetic resonance measurements in the smectic liquid crystalline phases of seven thermotropic compounds are reported, including terephthalbis(butylaniline), ethyl(methoxybenzylidene)amino] cinnamate, diheptyloxyazoxybenzinene, octyloxybenzoic acid, dipentylazoxycinnamate; diethylazioxcinnamic; dietHylazoxoxybenzosate; diheptonyloxy-benzene;
Abstract: Nuclear magnetic resonance measurements in the smectic liquid crystalline phases of seven thermotropic compounds are reported The compounds investigated are: terephthalbis(butylaniline); ethyl(methoxybenzylidene)amino] cinnamate; diheptyloxyazoxybenzene; octyloxybenzoic acid; dipentylazoxycinnamate; diethylazoxycinnamate; diethylazoxybenzoate Proton spectra at 100 MHz of the neat liquid crystal molecules, as well as of simple probe molecules dissolved in small amounts in the liquid crystal, were studied in their dependence on temperature and on sample orientation with respect to the magnetic field The results show that good alignment of the smectic phases can be obtained by cooling from the isotropic or the nematic phase in a magnetic field; once aligned, the smectic planes conserve their original orientation on rotation of the magnetic field The results are consistent with the following models of the smectic phases: Smectic‐A is uniaxial and there is fast rotational and translational molecular diffus
Abstract: A novel experimental procedure combining the measurement of (i) the flow velocity and (ii) the change in birefringence induced by laminar flow in a magnetic field has been used to determine the complete set of the five independent shear-viscosity coefficients of nematic liquid crystals The anisotropy of the magnetic susceptibility is obtained as well Results are reported for p'-methoxybenzylidene-p-n-butylaniline (MBBA), p-n-hexyl-oxybenzylidene-p'-aminobenzonitrile (HBAB), and a 1:1:1-molar mixture of HBAB with p-n-butoxybenzylidene-p'-aminobenzonitrile and p-n-octanoyl-oxybenzylidene-p'-aminobenzonitrile
TL;DR: In this article, the phase behavior of 35 N N, (p ‐alkoxybenzylidene) and p ‐n ‐alkylidene compounds, CnH2n + 1O−φ-CHN+CmH2m + 1′ with n values ranging from 1 to 7 and m from 4 to 8 by means of thermal microscopy and differential scanning calorimetry.
Abstract: We have investigated the phase behavior of 35 N ‐(p ‐alkoxybenzylidene)‐p ‐n ‐alkylaniline compounds, CnH2n + 1O–φ–CHN–φ–CmH2m + 1′ with n values ranging from 1 to 7 and m from 4 to 8 by means of thermal microscopy and differential scanning calorimetry. We report transition energies and entropies in addition to transition temperatures. From textures we determined the existence of nematic as well as smectic A, C, and B phases in many of the compounds. The microscopy and calorimetry evidence are consistent with a possible second order nature for the smectic C to smectic A transition. An interesting and useful smectic textural transition phenomenon is reported.
TL;DR: In this article, the structure and properties of disclination lines and disclination points in nematic and cholesteric liquid crystals are reviewed, and an equivalence between the directorfield of nematics and electrostatic or magnetostatic fields in two-dimensions is pointed out.
Abstract: Structure and properties of disclination lines and disclination points in nematic and cholesteric liquid crystals are reviewed. An equivalence between the directorfield of nematics and electrostatic or magnetostatic fields in two-dimensions is pointed out. Dislination lines can be classified in singular and non-singular lines. Disclination points correspond always to singular solutions. They are often associated with non-singular lines. Experimental observations of disclinations, of surface patterns in cholesterics, and of cholesteric textures are described. Structural features of special cholesteric “focal-conic” and “fan” texture are discussed in terms of the vectorfield defined by the twist axis.
Abstract: Raman-scattering techniques have been used to obtain a new quantitative measure of orientational statistics of individual molecules in a nematic liquid crystal. A marked discrepancy is observed between these measurements and the predictions of existing theories of nematic ordering.
TL;DR: In this paper, the nuclear magnetic resonance lineshape of the protons in the amphiphile alkyl chains in lamellar liquid crystals is calculated and it is found that the inclusion of intra molecular dipolar interactions not averaged to zero explains the shape of the experimentally observed spectrum.
Patent•
14 Feb 1973TL;DR: In this paper, the potential difference applied between the electrodes is applied by suitable means to determine the direction of propagation of the light beam in order to obtain a more complete view of the liquid crystal interface.
Abstract: The device comprises at least one liquid-crystal cell placed on the path of the beam and constituted by a film of liquid crystals interposed between two walls provided with electrodes between which a potential difference can be applied by suitable means. The incidence of the light beam is oblique with respect to the first wall-liquid crystal interface which is encountered. Use is made of liquid crystals for which the direction of propagation of the light beam is dependent on the potential difference applied between the electrodes.
TL;DR: In this paper, a new instability was observed in a smectic-A liquid crystal (CBOOA), submitted to a negative pressure across the layers, and the penetration length of de Gennes λ=(22±3) A.