Showing papers on "Liquid crystal published in 1986"

Field controlled light scattering from nematic microdroplets

Abstract: The light scattering and electro‐optic response of new material with display potential are investigated. The materials consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization. Droplet size, spacing, and distribution are readily controlled in these materials to allow optimization of displays based upon electrically controlled light scattering from the liquid crystal droplets. Preliminary experimental and theoretical studies of the light scattering properties show these materials to offer new features suitable for many display applications.

Polymer dispersed nematic liquid crystal for large area displays and light valves

Abstract: A new electro‐optical material based on nematic liquid crystal dispersed in a polymer matrix has recently been introduced by Fergason. This technology (termed NCAP, for nematic curvilinear aligned phase) is suitable for making very large area (thousands of square centimeter) light valves and displays. The device consists of micron size droplets of liquid crystal dispersed in and surrounded by a polymer film. Light passing through the film in the absence of an applied field is strongly forward scattered, giving a milky, translucent film. Application of an electric field across the liquid crystal/polymer film places the film in a highly transparent state. Pleochroic dyes may be employed in the system in order to achieve controllable light absorption as well as scattering. Microscopically, it is shown that the liquid‐crystal director lies preferentially parallel to the polymer wall, leading to a bipolar‐like configuration of the liquid‐crystal directors within the droplet. The symmetry axes of the droplets are randomly oriented in the unpowered, scattering state, but align parallel to the field in the powered, transparent state. The electric field required to reorient a given droplet varies inversely with the diameter of that droplet, and it is shown that the macroscopic electro‐optical properties of the film can be modeled if the distribution of liquid‐crystal droplet sizes is known.

Theory of lyotropic polymer liquid crystals

Abstract: Revue; influence du troisieme coefficient du viriel, de la charge, de la semiflexibilite de la bidispersite et de la polydispersite. Transition de phase isotrope nematique. Extension de la theorie d'Onsager

Birefringence dispersions of liquid crystals.

Abstract: The origins of liquid-crystal birefringence were investigated. Theory on the quantitative birefringence dispersions of liquid crystals was developed and found to have excellent agreement with experimental results throughout the entire visible and infrared spectral regions. New guidelines for selecting or synthesizing the liquid crystals with the desired birefringence are established. Novel applications of liquid crystals in the infrared region are foreseeable.

Existence and partial regularity of static liquid crystal configurations

Abstract: We establish the existence and partial regularity for solutions of some boundary-value problems for the static theory of liquid crystals. Some related problems involving magnetic or electric fields are also discussed.

Effect of electrostatic interaction on the liquid crystal phase transition in solutions of rodlike polyelectrolytes

Abstract: Cet effet peut etre caracterise par deux parametres, l'un decrivant l'augmentation du diametre effectif et l'autre, l'action twistante

Carbohydrate liquid crystals

Abstract: Certain alkyl l-O and l-S glycosides with hydrocarbon chain lengths greater than hexyl have been shown to form thermotropic liquid crystals at temperatures between 60 and 100[ddot]C. These are believed to be members of a large class of alkyl and acyl carbohydrate mesogens which, apart from their intrinsic value as potentially useful solid-state materials, could provide a variety of structurally accessible model systems for studying the phase transitions in the cell-membrane glycolipids.

Liquid crystalline-plastic material having submillisecond switch times and extended memory

Abstract: The invention provides a new liquid crystal-plastic display material having submillisecond switching times and an electrooptic bistable memory. The material comprises microdroplets of liquid crystal dispersed in a plastic matrix, the liquid crystal being present in an amount of at least 50% by weight. The material is prepared by the phase separation of a homogeneous solution of liquid crystal and synthetic polymer. Phase separation results in a liquid crystalline rich phase in the form of microdroplets and a plastic rich phase containing dissolved liquid crystal in solid solution with the plastic. The dissolved liquid crystal alters refractive index and the dielectric properties of the polymer, and lowers the temperature at which the plastic softens, making possible the fabrication of liquid crystal display materials having submillisecond switching rates and transparencies on the order of 90% and further having sufficiently high resistivity and permittivity so as to act as capacitors to maintain images for extended bistable memory.

The structure of thermotropic copolyesters

Abstract: Highly oriented polymeric products have been produced over the past fifteen years by two very different processing routes; from conventional polymers processed to highly oriented extended chain structures, and from “rod-like” polymers which exhibit liquid crystalline behaviour. Gel spun polyethylene is an example of such a conventional polymer. There are three main types of liquid crystalline polymers (LCP) which have high orientation and modulus: lyotropic aramids, such as poly(ρ-phenylene terephthalamide) (PPTA); lyotropic, aromatic heterocyclic polymers, or “ordered polymers”; and the family of thermotropic aromatic copolyesters. Extensive characterization of the thermotropic copolyesters has resulted in the delineation of a fibrillar, hierarchial structural model which accounts for the structures observed in a broad range of oriented fibres, extrudates and moulded articles. Three distinct fibrillar species are observed: microfibrils that are about 50 nm, fibrils about 500 nm, and macrofibrils about 5μm, in size. Superimposed on the structural hierarchy is a defect hierarchy, defined by the regular meander of the molecular chain and a localization of defects within a microfibril at about a 50 nm periodicity. Orientational variations, layering and skin core structures, in thick specimens, are the result of local flow fields on the basic structural units during solidification. The fibrillar textures appear to be present prior to any preparation for microscopy. A wide range of specimen preparation methods, i.e. fractography, sonication, microtomy and etching, and microscopic techniques, i.e. optical, scanning and transmission electron microscopy, were applied to the characterization of the aromatic copolyesters and PPTA. Interestingly, the same basic hierarchy is observed for both the lyotropic and the thermotropic LCPs and the microfibrillar structures of all the highly oriented polymers, including polyethylene, appear quite similar.

Liquid crystal filling device

Abstract: An improved liquid crystal filling device is shown. Prior to joining a substrate with another substrate between which the liquid crystal is to be charged, the liquid crystal is dropped on the substrate and then the other substrate is superimposed on the substrate under pressure. Sandwiched between the substrates, the liquid crystal spreads at high temperature.

Phase behavior and bilayer properties of fatty acids: hydrated 1:1 acid-soaps

Abstract: The physical properties in water of a series of 1:1 acid-soap compounds formed from fatty acids and potassium soaps with saturated (10-18 carbons) and omega-9 monounsaturated (18 carbons) hydrocarbon chains have been studied by using differential scanning calorimetry (DSC), X-ray diffraction, and direct and polarized light microscopy. DSC showed three phase transitions corresponding to the melting of crystalline water, the melting of crystalline lipid hydrocarbon chains, and the decomposition of the 1:1 acid-soap compound into its parent fatty acid and soap. Low- and wide-angle X-ray diffraction patterns revealed spacings that corresponded (with increasing hydration) to acid-soap crystals, hexagonal type II liquid crystals, and lamellar liquid crystals. The lamellar phase swelled from bilayer repeat distances of 68 (at 45% H2O) to 303 A (at 90% H2O). Direct and polarized light micrographs demonstrated the formation of myelin figures as well as birefringent optical textures corresponding to hexagonal and lamellar mesophases. Assuming that 1:1 potassium hydrogen dioleate and water were two components, we constructed a temperature-composition phase diagram. Interpretation of the data using the Gibbs phase rule showed that, at greater than 30% water, hydrocarbon chain melting was accompanied by decomposition of the 1:1 acid-soap compound and the system changed from a two-component to a three-component system. Comparison of hydrated 1:1 fatty acid/soap systems with hydrated soap systems suggests that the reduced degree of charge repulsion between polar groups causes half-ionized fatty acids in excess water to form bilayers rather than micelles.(ABSTRACT TRUNCATED AT 250 WORDS)

The structure and energetics of defects in liquid crystals

Abstract: The study of defects in ordered media has become a subject of considerable interest to condensed matter physicists in recent years. This article presents a systematic account of the structures, energies and interactions of defects in the nematic, smectic, cholesteric and discotic phases of liquid crystals. Relevant experimental observations are also described.

Liquid crystal matrix display having improved spacers and method of making same

Abstract: Light influencing displays and more particularly liquid crystal displays are disclosed which have a pair of light transmissive electrode supports which are uniformly spaced apart by a predetermined distance over the entire display area. The electrode supports are spaced apart by spacer means including a plurality of spacers arranged in a predetermined pattern between the electrode supports.

Liquid crystalline elastomers based on liquid crystalline side group, main chain and combined polymers

Abstract: Covalently crosslinked liquid crystalline networks with elastic properties were prepared in isotropic solution from linear liquid crystalline polymers. As linear precursors for the networks were used: (i) polymers with the mesogenic groups in the side groups (polyacrylates and polymethacrylates), (ii) polymers with the mesogenic groups in the main chain (polymalonates) and (iii) polymers with the mesogenic groups in main chain and side groups (“combined liquid crystalline polymers”). In all crosslinked polymers the liquid crystalline phases of the linear polymers are retained. For low degrees of crosslinking (≤2 mol-%) the phase transition temperatures remain nearly unchanged. These elastomers are very soft above Tg and can be easily stretched for more than 100%. For higher degrees of crosslinking the phase transition temperatures are reduced.

Viscosity Coefficients of Some Nematic Liquid Crystals

Abstract: The viscosity coefficients η1, η2 and η3 of 4-n-pentyl-4′-cyanobiphenyl (5CB), 4-n-octyl-4′-cyanobiphenyl (8 CB), 4-n-pentyloxy-4′-cyanobiphenyl (50 CB), and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) have been determined over their nematic phases. Using literature data for the temperature dependence of the order parameter S, given for 5CB, and 8CB, a relation between the anisotropy of viscosity coefficients and parameter S is discussed. Two models; first the Imura-Okano model, and the second, assumping a dependence between the term (ηi/ηiso − 1) and the order parameter, are analysed. For the second assumption much higher values of the correlation coefficients have been obtained. On the base of our own and Skarp's data for 5CB, it has been proved that the assumption of α3 ≅ 0 made for the elongated molecules is correct. Following this some anomalies observed for 8CB are discussed. The linear dependence obtained between the viscosity coefficients and the order parameter is analogous to the equations obt...

Collective rotation of molecules driven by the angular momentum of light in a nematic film.

Abstract: It is experimentally demonstrated that a circularly polarized laser beam normally incident on a homeotropically aligned nematic film can induce a collective precession of the molecules in the film if the laser intensity is above the threshold for the Freedericksz transition. The effect is shown to result from a transfer of angular momentum from the laser beam to the medium.

Two transitions in tangentially anchored nematic droplets

Abstract: In an axisymmetric approximation the author demonstrates a parity breaking transition to a twisted configuration in tangentially anchored nematic liquid crystal droplets The twisted phase occurs when K11>or=K22+0431K33 In a magnetic field there is another transition corresponding to the droplet axis changing from parallel to normal to the field

Liquid crystal droplets dispersed in thin films of uv- curable polymers

Abstract: Optically responsive films comprising birefringent nematic and/or birefringent chiral nematic liquid crystal microdroplets dispersed in UV-cured polymeric reaction products of di- and/or triallyl ethers and esters and suitable polythiols are disclosed.

Extreme swelling of a lyotropic lamellar liquid crystal.

Abstract: The evolution of the OBS/water/decane/pentanol lyotropic lamellar crystal is followed from 0% to more than 90% decane content. The lamellar spacing (d) varies then from 35 A to 11000 A. The swelling is followed with small angle x-ray scattering and the Bragg divergence in the intensity is found to disappear in moderately swollen lamellar crystal (d from 200 A up to 800 A) while the central scattering increases. More striking is the reappearance of the Bragg divergences observed by SAXS (d from 800 A to 1100 A) and for extremely swollen lamellar crystals in the angular distribution of scattered light (d from 2 000 A to 10 000 A). We discuss these observations along the lines of the recent models of swollen lamellar liquid crystals and in particular the apparent evolution of the dilute lamellae.

Liquid crystal display material comprising a liquid crystal dispersion in a thermoplastic resin

Abstract: The invention provides a new liquid crystal display material prepared by the phase separation of a homogeneous solution of liquid crystal and thermoplastic resin to create in situ microdroplets of liquid crystal within a set transparent resin matrix. The new display material is characterized by ease of fabrication and the ability to be reworked by simple heating and cooling of the thermoplastic resin containing microdroplets of liquid crystal. It has been discovered that such a material fabricated from a thermoplastic resin and a liquid crystal having a liquid crystalline phase to isotropic phase transition temperature above the softening temperature of the resin exhibits a reversible field-independent memory.

Alignment of liquid crystals which exhibit cholesteric to smectic C*phase transitions

Abstract: An alignment method for materials with cholesteric to smectic C* phase transitions is described. Ordering of the molecules, confined between glass plates which have been coated with a polymer and buffed, is achieved using an electric field. While the buffing direction defines the orientation of the long axis of the molecules, the electric field defines the direction of the layer tilt. In cells with only one buffed surface, polar surface interactions are thought to be responsible for producing monodomain specimens.

Computations of the phase equilibrium, elastic constants, and viscosities of a hard-rod nematic liquid crystal

Abstract: Using an iterative solution to the Onsager integral equation for the orientational distribution function of spherocylinders in the nematic liquid crystal phase, we have studied several aspects of the Onsager theory of nematic ordering. We find that the isotropic–nematic coexistence region becomes narrower as the ionic strength of the solution decreases. We also calculate the curvature elastic constants and the nematodynamic viscosities of the nematic phase as a function of particle concentration. The results are compared to experimental data.

Liquid crystal color display and method.

Abstract: A liquid crystal color display (20) with color layer(s) (2, 3, 4) including plural volumes of operationally nematic liquid crystal material (25) in a containment medium (22) that tends to distort the natural liquid crystal structure in the absence of a prescribed input, such as an electric field, and pleochroic dye (28) is included or mixed with the liquid crystal material in each layer. A technique is disclosed to make strong integral, generally fluid-tight capsules of dyed liquid crystal using cross-linking of polymers. A poly(methyl vinyl ether/maleic anhydride) dissolved in the dyed liquid crystal reacts with an ester, e.g. polyvinyl alcohol, to form the strong cross-linked capsule material.

Optical biaxiality of nematic LC-side chain polymers with laterally attached mesogenic groups

Abstract: Liquid crystalline polymers with mesogenic groups laterally attached to the polymer backbone were investigated by polarizing microscopy with respect to their optical properties. The nematic polymers were macroscopically oriented in a magnetic or electric field. Polarization microscopic investigations with convergent polarized light show optical biaxial behavior of the nematic phase.

Nematic ordering of 4‐n‐alkyl‐4’‐cyanobiphenyls studied by carbon‐13 NMR with off‐magic‐angle spinning

Abstract: A method called RHODIUM (removal of homonuclear dipolar coupling and the use of off‐magic‐angle spinning) can be applied effectively to study the carbon‐13 NMR of liquid crystals in natural abundance. In this method, the sample is spun rapidly (∼1 kHz) at an angle (θ) slightly less than the magic angle, so that the nematic director aligns along the spinning axis and the dipolar couplings are reduced by a factor of (3 cos2 θ−1)/2. Proton–proton dipolar couplings are removed by a special decoupling sequence (BLEW‐48) so that carbon–proton dipolar couplings can be readily identified. The coupling constants (DC–H) of individual carbons are obtained by using a two‐dimensional technique of separated local field spectroscopy. The RHODIUM method has been used to study the molecular ordering in the nematic phase of 4‐n‐alkyl‐4’‐cyanobiphenyls (kCB). Three homologs (5CB, 6CB, and 7CB) were investigated at TNI−T =4 K. Values of DC–H of the aliphatic carbons give rich information on the energetics of chain conformati...