Showing papers on "Liquid crystal published in 1982"

Smectic liquid crystals

Abstract: The use of a certain class of liquid crystal materials that exhibit a smectic C phase allows the production of a bistable liquid crystal display element. Such bistable display elements promote the use of matrix addressing for liquid crystal based elements in a display.

Encapsulated liquid crystal and method

Abstract: Briefly, according to one aspect of the invention, liquid crystal material, and especially nematic material, is encapsulated; according to another aspect the encapsulated liquid crystal material is used in liquid crystal devices, such as relatively large size visual display devices; and according to further aspects there are provided methods for encapsulating liquid crystal material and for making a liquid crystal device using such encapsulated liquid crystal material.

Boundary-layer phase transition in nematic liquid crystals

Abstract: Phase-transition properties of nematic liquid crystals aligned by a short-range, arbitrary-strength-substrate potential are examined in the framework of Landau---de Gennes theory. It is shown that the substrate potential, which can arise from surface treatment of liquid-crystal display cells, not only induces a boundary layer in which the order-parameter values can be significantly different from that of the bulk, but also introduces a new "boundary-layer phase transition" which occurs at temperatures higher than the bulk-transition temperature. This novel transition is found to take place only in a limited range of substrate potential strength. For 4-pentyl-4'-cyanobiphenyl (PCB), the limiting values of this range are computed to be \ensuremath{\sim}0.075 and \ensuremath{\sim}0.15 erg/${\mathrm{cm}}^{2}$. Calculations are performed for both the semi-infinite-sample case and the finite-thickness-sample case. Various phase diagrams are presented to show the effects of sample thickness and substrate potential on the bulk as well as the boundary-layer phase-transition temperatures. The paper concludes with a discussion of experimental possibilities.

A theory of orientational ordering in uniaxial liquid crystals composed of molecules with alkyl chains

Abstract: The constituent molecules of thermotropic liquid crystals invariably contain an aromatic core to which is attached one and often two n -alkyl chains. Nuclear magnetic resonance investigations have revealed that the chain does not exist entirely in an all- trans configuration and that the orientational order of the methylene groups varies markedly along the chain. In this paper we develop a theory to explain these variations for a uniaxial phase at a given temperature and pressure. Our theory contains two distinct parts: one is a model for the conformational distribution of the alkyl chains while the other is for the potential of mean torque experienced by a conformer and which is responsible for its alignment with respect to the director. We use the rotameric state model developed by Flory to describe the conformations adopted by the alkyl chain. The potential of mean torque presents a more difficult problem and we assume that it may be represented by a sum of contributions from each rigid group in the molecule. The order parameters for the methylene and methyl groups in the alkyl chains of the 4- n -pentyl and 4- n -octyl-49-cyanobiphenyls predicted by the theory are found to be in good accord with those obtained experimentally. We have also used the theory to predict the conformational distributions for both the isotropic and nematic phases of these mesogens; the calculated distributions are contrasted with those assumed by other models. In addition we have obtained the ordering matrices for the various conformers adopted by the two 4- n -alkyl-49-cyanobiphenyls. The results of these calculations do not support the notion that the orientational order of such molecules can be described by a single, cylindrically symmetric ordering matrix.

Rotational viscosity γ1 of nematic liquid crystals

Abstract: The rotational viscosity coefficients γ1 are measured with the rotating field method as a function of temperature in the nematic phases of 4‐methoxybenzylidene‐4′‐n‐butylaniline, 4‐n‐pentyl‐, and 4‐n‐octyl‐4′‐cyanobiphenyl, of the eutectic mixture of two 4‐n‐pentylphenyl 4‐alkoxybenzoates and of the eutectic mixture of the two isomers of 4‐methoxy‐4′‐n‐butylazoxybenzene. Equations are proposed which describe the temperature dependence very well. The Leslie coefficients αi are calculated from the γ1 values and recently measured shear viscosity coefficients.

New display based on electrically induced index‐matching in an inhomogeneous medium

Abstract: The operation of a new light modulation device that employs electric field controlled light scattering in an inhomogeneous medium is described. The orientation of a nematic liquid crystal, contained in micrometer sized inclusions in a nonabsorbing solid, is changed to produce a varying refractive index. When the refractive index of the liquid crystal matches that of the solid, the composite medium is nonscattering and transparent. If the refractive indices do not match, the medium is scattering and opaque. High contrast ratios have been measured for transmitted light with a response time of a ∼1 ms. The application of this technique to passive display devices is discussed.

Theory of spin‐lattice relaxation in lipid bilayers and biological membranes. 2H and 14N quadrupolar relaxation

Abstract: Based on a previous, more approximate treatment [M. F. Brown, J. Magn. Reson. 35, 203 (1979)], expressions are derived for the quadrupolar spin‐lattice (T1) relaxation rates of 2H and 14N in lipid bilayers. Results are presented for the most general, anisotropic rotational diffusion model describing the segmental or molecular reorientation in lipid bilayers, and the analysis is extended to include relatively slow fluctuations of the local director with respect to the macroscopic bilayer normal. Numerically computed values of T1 for the diffusion model suggest that, even for extremes of ordering and motional anisotropy, such a model cannot by itself quantitatively account for the observed 2H T1 values of multilamellar dispersions of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC), in the liquid crystalline state, as a function of temperature and frequency. The contribution from relatively low frequency motions is modeled in terms either (i) a simple noncollective model in which the slow motions are described in terms of a single effective correlation time, or (ii) a collective model in which the relatively slow reorientation is described by a distribution of correlation times, corresponding to collective fluctuations of the instantaneous director. The experimentally observed dependence of the 2H T1 relaxation rates on the acyl chain segmental order parameter SCD and the resonance frequency ω0 are most consistent with a collective model for slow molecular reorientations in lipid bilayers. The 2H T1 data for the saturated DPPC bilayer, in the liquid crystalline state, can be quantitatively described by a relaxation law of the form T−11 = Aτf+BS2CD ω−1/20 as observed for simpler nematic and smectic liquid crystals. The first (A) term is suggested to correspond to trans–gauche isomerizations of the lipid acyl chains, while the (B) term describes collective bilayer modes which predominantly influence the frequency dependence of the relaxation. In contrast to earlier conclusions [M. F. Brown et al., J. Chem. Phys. 70, 5045 (1979)], the dominant contribution to the 2H T1 relaxation rates of the saturated DPPC bilayer may arise from collective order fluctuations rather than fast local motions. The value of τf∼10−11 s obtained by extrapolating T−11 to infinite frequency or zero ordering is consistent with the correlation times calculated from 2H or 13C T1 data for n‐alkanes of equivalent chain lengths, suggesting that the microviscosity of the bilayer hydrocarbon region is not appreciably different from that of paraffinic liquids.

Liquid crystal light valve using bulk monocrystalline Bi 12 SiO 20 as the photoconductive material

Abstract: A new liquid crystal light valve (LCLV) is presented using bulk monocrystalline Bi12SiO20 (BSO) as both the photoconductive material and as one of the substrates supporting the liquid crystal layer. The photoconductive properties of the BSO under ac voltages are investigated. The device operates at room temperature with a low ac drive voltage (25-V ac at 500 Hz). These specific properties are explained from the aspect of an equivalent electrical circuit of the structure. A prototype BSO LCLV with a 15-μm liquid crystal thickness shows a 10-lp mm−1 spatial resolution. The device coherent modulation transfer function was measured experimentally and found to agree with theory. Typical writing energies are ~20 μJ cm−2 at wavelength λ = 450 nm.

Electron‐spin relaxation and ordering in smectic and supercooled nematic liquid crystals

Abstract: We report on careful line shape studies of slow motional and orientation dependent ESR spectra of a deuterated liquid‐crystal‐like spin probe dissolved in a benzilidene‐derivative (40,6) and in cyanobiphenyl derivative (S2 and 5CB) liquid crystals. The simulation of the ESR spectra is based on the Lanczos algorithm recently applied by Moro and Freed in a general and efficient formulation of slow motional and ordering effects on ESR line shapes. With 40,6 which exhibits monolayer smectic phases, we find that the main change in the spin relaxation upon passing from the nematic to the smectic A phase consists of changes occuring in ordering attributable to packing forces on functional groups. Such ordering effects appear to be further enhanced in the SB phase with consequent alterations in dynamics. With S2, which exhibits an interpenetrating bilayer smectic A phase, we find unusual ESR spectra in that phase which may be simulated on the basis of a model of cooperative distortions static on the ESR time scale, and superimposed on individual molecular reorientation. This mode is interpreted as a collective chain distortion which affects the orientational distribution of the piperidine ring of the spin probe. A similar phenomenon is observed in the supercooled nematic phase of 5CB, which is aligned by an electric field, and evidence is also found that the reorientational dynamics of this ring are affected by interaction with local cooperative modes in the liquid crystal (i.e., a SRLS mechanism previously proposed by Freed and co‐workers). Some microscopic characteristics of liquid crystals revealed by this and previous ESR spin probe studies are discussed.

Rheology of a thermotropic polyester in the nematic and isotropic states

Abstract: The rheological properties of a thermotropic polyester were determined in the nematic and isotropic states. In the isotropic state, the viscosity is almost constant and the polymer is only slightly elastic. The nematic phase has a lower viscosity than the isotropic, except at low frequencies or shear rates, where the viscosity increases as though the polymer had a yield stress. There is a marked dependence of the rheology on shear history. The effects of shearing can be erased by returning the material first to the isotropic state and then back to the nematic state. The results are discussed with reference to analogous observations in small-molecule liquid crystals and in thermotropic aromatic co-polyesters.

Lyotropic liquid crystals

Abstract: In mixtures of soap and water, the special properties of soap molecules cause them to form clusters—and clusters of clusters—in a variety of interesting geometrical shapes. Some of these aggregates are liquid crystals, known as lyotropic, which are quite different from thermotropic liquid crystals, the focus of most of the work described in this issue of PHYSICS TODAY. Lyotropic liquid crystals are now receiving a great deal of scientific and technological attention because of the way they reflect the unique properties of their constituent molecules.

Manufacture of liquid crystal display body device

Abstract: PURPOSE:To inject a liquid crystal into a cell exactly in a short time, by dripping the liquid crystal from a dispenser to a trumpetlike liquid crystal injecting port of a liquid crystal cell placed in an airtight vessel kept in a vacuum state, and after that, pressurizing the inside of the vessel. CONSTITUTION:A liquid crystal display body cell 6 whose substrate is made of a synthetic resin film having a trumpetlike liquid crystal injecting port 6A is placed in an airtight vessel 5, and in the upper direction of this cell 6, a dispenser tip part 12 having a small hole 12A is fixed to a work table 10 which can be rotated up and down and to the right and left. Subsequently, the inside of the vessel 5 is made to a vacuum state by opening a valve 13, the table 10 is moved and is controlled so that a distance between the injecting port 6A and the hole 12A of the tip part 12 becomes constant, and after that, from a liquid crystal vessel 8 which has been cut off from the open air, a liquid crystal 7 of a constant quantity is dripped into the injecting port 6A through a dispenser 9, a feed pipe 11, the tip part 12 and the hole 12A. Subsequently, the inside of the vessel 5 is returned to the atmospheric pressure by opening a valve 14, and the liquid crystal 7 is injected into the cell 6.

Nematic and cholesteric thermotropic polyesters with azoxybenzene mesogenic units and flexible spacers in the main chain

Abstract: Properties of linear polyesters based on azoxybenzene and 2,2′-methylazoxybenzene moieties with linear, flexible spacers based on mixtures of dodecanedioic acid (DDA) and methyladipic acid (MAA), chiral or racemic, of various compositions (system MAA/DDA-8 and MAA/DDA-9, respectively) have been described Substitution of methyl groups in the 2,2′ or 3,3′ positions of the mesogenic core leads to soluble and relatively low-melting-point polyesters The viscosity law for (MAA/DDA-9) polyesters in 1,1,2,2 tetrachloroethane gives an exponent 076, indicating well-sol-vated, coiled chain conformations in dilute solution Calorimetric data show an increase in isotropization entropy ΔSNI with increasing average length of the spacer This suggests a nonrandom conformation of the spacer in the nematic melt with a degree of order superior to that of low-molecular-weight analogs X-ray data obtained with an oriented nematic glass quenched from the nematic melt of DDA-9 subjected to a magnetic field of 10–12 T also support the extended-chain model in the nematic phase of DDA-9 Oriented fibers can be produced by subjecting nematic melts of polyesters 8 and 9 either to magnetic fields of high intensity or to shear fields The x-ray data obtained from these fibers also support the extended-chain model Cholesteric systems do not orient in the magnetic field of 10–12 T The study of mesophases of systems 8 and 9 indicates a dramatic influence of the position of the ester group on the stability of the mesophase in the azoxybenzene polyesters The results are interpreted in terms of geometric factors influencing the colinearity of the mesogenic core and of the extended spacer

Odd‐even effects in polymeric liquid crystals

Abstract: Semiflexible mesophasic polymers of the general formula and where and are prepared and their solid and liquid crystalline behaviour examined and compared to that of the corresponding homologues with n even. Evidence is given of relevant odd-even effects in the thermodynamic parameters of the clearing transition. The conclusion is drawn in favour of an anisotropic structuration also of the flexible parts of the polymer chain in the liquid crystal phase.

Liquid Crystal Polymers. V. Thermotropic Polyesters with Either Dyad or Triad Aromatic Ester Mesogenic Units and Flexible Polymethylene Spacers in the Main Chain

Abstract: The thermal properties of two new series of thermotropic, liquid crystalline polyesters were studied by differential scanning calorimetry and on a hot-stage of a polarizing microscope. The first series contained an aromatic ester triad with a central terephthaloyl and two terminal oxybenzoyl units connected by a flexible polymethylene spacer containing from two to ten methylene units. The second series contained a head-to-head tail-to-tail aromatic ester dyad with one terephthaloyl and one oxybenzoyl unit and either a dimethylene or hexamethylene spacer. The melting temperatures and the transition temperatures for conversion from the mesophase to the isotropic phase (the clearing temperature) of the polyesters in the first series initially decreased in a zig-zag manner for polymers with up to nine methylene units but increased for the decamethylene polymer. The temperature ranges over which the mesophase formation occurred were generally broader for polymers containing an odd number of methylene units than for those with an even number of units. Most, if not all, of the polymers in both series formed nematic states on melting. The enthalpy and entropy changes for the clearing transition both increased with the length of the polymethylene spacer. Polymers of the second series possessed lower transition temperatures and narrower temperature ranges for mesophase formation, as would be expected for the shorter mesogenic unit.

Microscopic one-particle description of reentrant behavior in nematic liquid-crystals

Abstract: Reentrant behavior in nematic liquid crystals is described by the treatment of the system as a mixture of monomers and dimers interacting through attractive induced soft interactions as well as hard-core repulsions It is shown that the induced forces between dimers, monomers, and between monomers and dimers, respectively, under suitable conditions of temperature and density lead to a smectic layer structure with a period equal to the length of the dimer However, with decreasing temperature or increasing density, repulsive steric forces, due to the unfavorable packing of the dimers in the smectic planes, may take over and thus favor the nematic phase again In agreement with experiment the best conditions to get a reentrant nematic phase are predicted for the ratio of the length of the dimer to that of the monomer between 13 and 14 The predictions of the model are in good agreement with currently available experimental data In principle, the model applies also to discotic liquid crystals

Director dynamics and NMR applications of nematic liquid crystals spinning at various angles from the magnetic field

Abstract: The dynamics of the director of a nematic liquid crystal spinning in a magnetic field are studied. A simple average potential theory which gives a qualitative understanding of the director behavior is presented along with an exact quantitative treatment of situations in which the director is stationary in the laboratory frame. NMR spectra of an A2 spin system, 19F in CF2CBr2, are used to verify the theory. For nematic liquid crystals in which the magnetic susceptibility anisotropy Δχ = (χ∥−χ⊥) is positive, the director aligns along the spinning axis when the sample is spun at a rate much greater than that characteristic of director reorientation and the angle between the spinning axis and the magnetic field is less than the magic angle ϑm = 54.74°. Past the magic angle the director distributes in the plane perpendicular to the spinning axis. For liquid crystals in which Δχ is negative, alignment parallel to the spinning axis occurs for angles greater than ϑm and distribution in the plane occurs for angles...

Diamagnetism and orientational order of nematic liquid-crystals

Abstract: Measurements are presented for the diamagnetic anisotropy of thirteen nematic liquid crystals. As any bias in the rotation around the long molecular axis is most probably small, the results probe accurately the temperature variations of S, the degree of orientational order. The critical behaviour of S near the nematic-isotropic phase transition can be described by an exponent 03B2 of the order of 0.25. Procedures are considered to obtain the molecular magnetic anisotropy. By a systematic variation of the structure of the molecules an impression of the contributions of the various molecular groups can be obtained It turns out to be rather difficult to obtain accurate data for the molecular magnetic anisotropy. As a consequence the absolute scale of S can only be fixed with an accuracy of the order of 10 %. J. Physique 43 (1982) 361-367 FTVRIER 1982,

Liquid crystalline side chain polymers and their behaviour in the electric field

Abstract: The electro-optical properties of liquid crystalline polymers with polar mesogenic units in the side chain were investigated. It could be shown, that in an electric field, they show all effects known from low molecular weight liquid crystals, e.g. the Freedericksz-transition, the DAP-effect, the formation of William's domain, and the dynamic scattering. The optical response times are slightly longer than for low molecular weight liquid crystals, but in some cases at higher temperatures as short as 200 ms. By comparison of different polymers and some corresponding liquid crystalline monomers, it is found that: (1) the difference between the measuring temperature and the glass transition temperature mainly determines the optical response times, (2) the fixation of mesogenic groups to a polymer main chain via spacers influences the threshold voltage. Low values are found for long spacers. These results allow a discussion of the influence of polymer fixation of the mesogenic groups on their liquid crystalline properties, pointing to a partial decoupling of the motions of main chains and side chains.

Chain ordering and molecular orientational order in liquid crystals

Abstract: We have extended the scheme for computing deuterium quadrupolar splittings of a flexible solute in a nematic solvent [Ferroelectrics 30, 83 (1980)] to study chain ordering in the 4‐n‐alkyl‐4′‐cyanobiphenyl liquid crystals (nCB). All possible configurations {φ} of the nCB molecule are generated by the rotational isomeric state model of Flory. Each {φ} has a separate ordering matrix whose diagonal elements are assumed to scale with the shape anisotropy of the molecule as prescribed by the principal moments of inertia of the configuration I{φ}. Two models for identifying the molecular‐fixed‐frame are considered: (1) The frame diagonalizes I{φ}; (2) the frame is stationary on the nCB core. The variation of deuterium quadrupolar splittings along the alkyl chain can be satisfactorily explained by the calculations, however, the detailed behavior of the computed splittings are sensitive to the assumptions about the placement of the molecular‐fixed‐frame.

Method and apparatus for converting phase-modulated light to amplitude-modulated light and communication method and apparatus employing the same

Abstract: A light modulator for generating a beam of amplitude-modulated light including a source of polarized light, at least one and preferably two liquid crystal cells having a thin layer of nematic liquid crystals of positive dielectric anisotropy through which the polarized light is directed to produce a beam of light having a phase shift corresponding to a modulating electrical signal which is applied to each of the liquid crystal cells. The liquid crystal cells in addition have a continuing electrical bias applied across the layers in order to achieve the rapid response times necessary to achieve phase modulation of the polarized light. The resulting phase-modulated light is converted in a linear polarizer to amplitude-modulated light corresponding to the modulating electrical signal. The amplitude-modulated light is detected in a suitable light detector which generates an electrical signal corresponding to the modulating electrical signal. The linear polarizer may be oriented with either the transmitter or the receiver. A communication system involving a transmitting modulator and a receiving demodulator transmits communication through light either as phase-modulated light or as amplitude-modulated light.

Liquid crystal mixture

Abstract: There is described a liquid crystalline mixture for electro-optical devices which are operated according to the two-frequency matrix addressing procedure. The mixture consists of three components A, B and C, each of which contains one or more compounds. Component A has a viscosity of at most about 40 cp, a clearing point of at least about 40° C. and a dielectric anisotropy between about -2 and about +1. Component B has a dielectric anisotropy below about -2 both above and below the cross-over frequency of the total mixture and component C has a dielectric anisotropy above about +10, a clearing point of at least about 100° C. and there is a cross-over frequency in the total mixture of at most about 15 kHz at 20° C. Novel compounds for such mixtures and their manufacture and use are also described. The novel mixtures make possible especially high multiplex rates and short response times.