Showing papers on "Liquid crystal published in 1997"
TL;DR: The approach promises to improve the accuracy of structures determined by NMR, and extend the size limit, and distances and angles derived from dipolar couplings in human ubiquitin are in excellent agreement with its crystal structure.
Abstract: In isotropic solution, internuclear dipolar couplings average to zero as a result of rotational diffusion. By dissolving macromolecules in a dilute aqueous nematic discotic liquid-crystalline medium containing widely spaced magnetically oriented particles, a tunable degree of solute alignment with the magnetic field can be created while retaining the high resolution and sensitivity of the regular isotropic nuclear magnetic resonance (NMR) spectrum. Dipolar couplings between1H-1H, 1H-13C,1H-15N, and 13C-13C pairs in such an oriented macromolecule no longer average to zero, and are readily measured. Distances and angles derived from dipolar couplings in human ubiquitin are in excellent agreement with its crystal structure. The approach promises to improve the accuracy of structures determined by NMR, and extend the size limit.
1,634 citations
TL;DR: A smectic liquid-crystal phase made from achiral molecules with bent cores was found to have fluid layers that exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering about the layer normal and molecular tilt.
Abstract: A smectic liquid-crystal phase made from achiral molecules with bent cores was found to have fluid layers that exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering about the layer normal and molecular tilt. These instabilities combine to form a chiral layer structure with a handedness that depends on the sign of the tilt. The bulk states are either antiferroelectric-racemic, with the layer polar direction and handedness alternating in sign from layer to layer, or antiferroelectric-chiral, which is of uniform layer handedness. Both states exhibit an electric field-induced transition from antiferroelectric to ferroelectric.
1,041 citations
TL;DR: Small water droplets dispersed in a nematic liquid crystal exhibit a novel class of colloidal interactions, arising from the orientational elastic energy of the anisotropic host fluid, which can lead to novel mechanisms for colloid stabilization.
Abstract: Small water droplets dispersed in a nematic liquid crystal exhibit a novel class of colloidal interactions, arising from the orientational elastic energy of the anisotropic host fluid. These interactions include a short-range repulsion and a long-range dipolar attraction, and they lead to the formation of anisotropic chainlike structures by the colloidal particles. The repulsive interaction can lead to novel mechanisms for colloid stabilization.
1,032 citations
496 citations
TL;DR: In this article, the stiffness of cylindrical supramolecular dendrimers was evaluated by examining their planar texture and its defects, showing that they are self-assembled, self-organized, and aligned spontaneously and simultaneously in hexagonal columnar or cubic thermotropic liquid-crystal phases with high uniformity.
Abstract: Electron microscopy methods have been used to visualize individual spherical and cylindrical supramolecular dendrimers, providing definitive confirmation of the structures suggested by previous x-ray diffraction analysis that assumed a microsegregated model. These dendrimers are self-assembled, self-organized, and aligned spontaneously and simultaneously in hexagonal columnar or cubic thermotropic liquid-crystal phases with high uniformity. Homeotropic and planar ordering of the hexagonal columnar liquid crystal was precisely controlled by a variety of surfaces. The stiffness of these cylinders was evaluated by examining their planar texture and its defects.
480 citations
TL;DR: In this article, a review of liquid crystal material properties and electro-optical effects that essentially determine the performance of twisted nematic displays are reviewed, including dual-frequency addressing phenomena in liquid crystal materials, in situ dielectric heating of displays, and conductivity phenomena that may either hamper or improve performance of high information content LCDs.
Abstract: Since the early 1970s, three major prerequisites have brought the success of the liquid crystal display (LCD) technology to its key role of today. Namely, the discovery of electro-optical field-effects on which the displays are based, the successful search for liquid crystals (LCs) with material properties that meet the complex requirements of electro-optical effects and render the effects applicable in displays, and last but not least, the development of the technological tools required for manufacturing displays. Virtually all of today’s commercial LCDs are based on the twisted nematic (TN) or on various supertwisted nematic (STN) effects whose extensive development and improvement over the past 25 years is still rapidly progressing. Those liquid crystal material properties and electro-optical effects that essentially determine the performance of nematic displays are reviewed. Correlations between molecular functional structural groups, LC material properties, and their electro-optical relevance for TN and STN displays are outlined. Included are dual-frequency addressing phenomena in liquid crystal materials, in situ dielectric heating of displays, and conductivity phenomena that are related and that may either hamper or improve the performance of high-information content LCDs. Moreover, we review some recent developments made in our laboratories on novel electro-optical devices and device-specific functional organic materials, e.g. optical alignment of monomeric and polymeric liquid crystals by linearly polarized light; the generation of photo-patterned multidomain twisted nematic displays with broad field of view; the operation of displays with circularly polarized light, as well as compact and bright cholesteric LCD projection optics whose polarizers, filters, and modulators are all based on liquid crystal elements.
443 citations
391 citations
Patent•
06 Jan 1997TL;DR: In this paper, a method for the loading and alignment of elastomers in electro-optic and electro-active devices is described, which comprises the in-situ polymerisation between substrates of liquid crystal monomers in the presence of cross-linking reagents.
Abstract: This invention describes a method for the loading and alignment of elastomers in electro-optic and electro-active devices. It comprises the in-situ polymerisation between substrates of liquid crystal monomers in the presence of cross-linking reagents. It also describes the production of free-standing elastomer films.
364 citations
Patent•
15 Dec 1997
TL;DR: In this paper, a liquid crystal display device with a pair of substrates and a liquid-crystal layer provided between the substrates is described, where liquid crystal molecules in the liquid crystal layer have a negative dielectric anisotropy and are aligned in a direction substantially vertical to the substrate when no voltage is being applied and axis-symmetrically aligned in each of a plurality of pixel regions under application of a voltage.
Abstract: A liquid crystal display device of the present invention includes a pair of substrates and a liquid crystal layer provided between the substrates, wherein liquid crystal molecules in the liquid crystal layer have a negative dielectric anisotropy, and the liquid crystal molecules are aligned in a direction substantially vertical to the substrates when no voltage is being applied and are axis-symmetrically aligned in each of a plurality of pixel regions under application of a voltage.
343 citations
TL;DR: In this article, a block copolymer was synthesized by anionic polymerization of poly(styrene-b-1,2/3,4-isoprene) followed by corresponding polymer analogous reactions, and the effect of chemical structure on surface properties and the influence of liquid crystalline structure of the semifluorinated side chain on the surface behavior were evaluated.
Abstract: Monodisperse poly(styrene-b-semifluorinated side chain) block copolymers were synthesized by anionic polymerization of poly(styrene-b-1,2/3,4-isoprene) followed by the corresponding polymer analogous reactions. By controlling the block copolymer composition and the relative lengths of the fluorocarbon and hydrocarbon units in the side group, the effect of chemical structure on surface properties and the influence of liquid crystalline structure of the semifluorinated side chain on the surface behavior were evaluated. The composition of side groups does not greatly affect the as-prepared sample surface tension, but influences instead the transition temperatures of the room temperature liquid crystal phase. It was observed that the shorter fluorocarbon units (six −CF2− units) form a smectic A phase at room temperature. The critical surface tension of the SA phase is 10.8 mN/m, and the polymer surface undergoes significant reconstruction when immersed in water. However, when the fluorocarbon side chain conta...
315 citations
TL;DR: In this paper, the macroscopic orientational ordering of the pores of condensed hexagonal mesostructured silica (MCM-41) was achieved through alignment of an unpolymerized, hexagonal, lyotropic silicate-surfactant liquid crystal in a high magnetic field.
Abstract: Macroscopic orientational ordering of the pores of condensed hexagonal mesostructured silica (MCM-41) was achieved through alignment of an unpolymerized, hexagonal, lyotropic silicate-surfactant liquid crystal in a high magnetic field. This alignment was preserved after polymerization of the silicate species by acid treatment. Subsequent calcination to remove the surfactant yielded a mesoporous silica solid that retained both macroscopic pore alignment and mesoscale periodicity. Potential applications of such liquid crystal processing strategies range from the formation of anisotropic silica-based bulk ceramics to the production of oriented mesoporous thin films for chemical sensors, separations, catalysis, or host-guest applications.
TL;DR: In this paper, stable colloidal suspensions of cellulose crystallites with negatively charged sulfate groups on their surface were prepared by acid hydrolysis of filter paper, and the suspensions, which were free of added electrolyte, formed chiral nematic ordered phases above a critical concentration.
Abstract: Stable colloidal suspensions of cellulose crystallites with negatively charged sulfate groups on their surface were prepared by acid hydrolysis of filter paper. The suspensions, which were free of added electrolyte, formed chiral nematic ordered phases above a critical concentration. A sharp boundary was observed between coexisting chiral nematic and isotropic phases, enabling measurements to be made of the relative amounts of each phase as a function of total cellulose concentration. The isotropic-to-chiral nematic phase equilibrium was sensitive to the nature of the counterions present in the suspension. Samples were prepared with sodium, potassium, cesium, ammonium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, trimethylammonium, and triethylammonium counterions. Suspensions with H+ counterions formed an ordered phase at the lowest concentrations of crystallites. For inorganic counterions, the critical concentration for ordered phase formation increases in the order ...
TL;DR: The origin of the helix is discussed in view of the twisted molecular conformation (conformational chirality) and the escape from macroscopic polarization in this paper.
Abstract: Helical structures were confirmed for both the SmAb and SmBlue phases of banana-shaped molecular systems from observations of the microscopic fringe pattern and the selective reflection of blue color, respectively. X-ray and optical microscopy indicate that the helical axes in the SmAb and SmBlue phases are normal and parallel to the smectic layer, respectively. In these two helical phases, 13C NMR spectra show two C=O peaks, suggesting two different configurations of ester group, whereas only one C=O peak appears in the isotropic and crystal phases. This indicates that the two C=O groups in the mesogenic core are not in the same plane but are twisted. The addition of chiral dopant makes the dichroic ratio of the right- and left-circularly polarized scattered light positive or negative in the SmBlue phase, although the wavelength (?430 nm) of the scattering peak does not change significantly. The origin of the helix will be discussed in view of the twisted molecular conformation (conformational chirality) and the escape from macroscopic polarization.
TL;DR: In this article, a set of surfaces formed by chemisorption of alkanethiols on ultrathin films of gold permit control of both the azimuthal and polar orientations of supported nematic liquid crystals (LCs).
Abstract: Molecularly designed surfaces formed by chemisorption of alkanethiols on ultrathin films of gold permit control of both the azimuthal and polar orientations of supported nematic liquid crystals (LCs). These surfaces, when patterned, form simple and versatile templates for the fabrication of complex optical structures from LCs. Surfaces patterned with odd or even alkanethiols, or mixtures of long and short alkanethiols, were used to fabricate tunable, micrometer-scale LC diffraction gratings that differed in their polarization sensitivity. Patterned alignment of LCs on curved surfaces is also demonstrated, thereby providing principles for fabrication of optical elements that combine diffractive and refractive optics.
TL;DR: In this article, the authors used multinuclear (2H, 13C, 29Si, 81Br) magnetic resonance spectroscopy, small-angle X-ray scattering, and polarized optical microscopy techniques to investigate molecular and mesoscopic organization in silicate−surfactant lyotropic liquid crystals with hexagonal and lamellar morphologies under highly alkaline conditions.
Abstract: Multinuclear (2H, 13C, 29Si, 81Br) magnetic resonance spectroscopy, small-angle X-ray scattering, and polarized optical microscopy techniques have been used to investigate molecular and mesoscopic organization in silicate−surfactant lyotropic liquid crystals with hexagonal and lamellar morphologies under highly alkaline conditions. Such systems cooperatively self-assemble following the addition of a basic aqueous solution containing anionic silicate oligomers (e.g., double-four-ring species) to an isotropic micellar solution of cationic surfactant molecules (e.g., cetyltrimethylammonium bromide). Important similarities and differences are shown to exist between multicomponent silicate−surfactant and conventional binary lyotropic liquid crystals. Under highly alkaline conditions, the silicate−surfactant systems possess the characteristics of ordinary lyotropic liquid crystalline systems, though the balance of forces underlying their self-assembly is complicated by the richness of the aqueous silicate chemi...
Book•
01 Jan 1997
TL;DR: Physical properties of thermotropics basic nonlinear optics light-induced reorientation thermal effects linear and nonlinear optical properties of PDLC this article have been studied in this article.
Abstract: Physical properties of thermotropics basic nonlinear optics light-induced reorientation thermal effects linear and nonlinear optical properties of PDLC.
TL;DR: In this paper, a method to measure attractive interactions between colloidal particles, and determine the nature of the attraction between particles suspended in a nematic liquid crystal, is presented. But the method is limited to a single colloidal particle.
Abstract: We present a new method to measure attractive interactions between colloidal particles, and determine the nature of the attraction between particles suspended in a nematic liquid crystal. We confine droplets filled with ferrofluid to a thin layer and apply a magnetic field to induce dipole moments that drive the droplets apart. When the field is removed, the attractive interactions pull the droplets back together. The force is determined from the velocity because the motion is viscously damped. We confirm the dipolar character of the interaction between droplets in a nematic solvent.
TL;DR: In this paper, the authors presented a surface-controlled bistable nematic liquid crystal display with simple monostable planar anchorings and a dielectrically positive nematic.
Abstract: We present a novel surface-controlled bistable nematic liquid crystal display. This black and white device uses simple monostable planar anchorings and a dielectrically positive nematic. The two bistable textures are, respectively, quasiuniform U and almost half-turn twisted T. Short electric pulses break the surface anchorings. Hydrodynamically coupled breaking of both anchorings creates T. U is obtained by breaking only one anchoring. Write and erase times for high resolution video are achieved at voltages compatible with the usual drivers.
TL;DR: In this paper, the contribution of both photoisomerization and photodimerization to liquid crystal alignment photoregulation was analyzed and the relationship between photoproduct distribution and liquid crystal photoalignment and on the reversibility of the photoinduced reorientation of a liquid crystal was concluded.
Abstract: Photoproduct distribution in films of cinnamate polymers was analyzed to reveal the contribution of both photoisomerization and photodimerization to LC alignment photoregulation. A polymethacrylate with o-cinnamate side chains displayed preferential formation of Z-isomer while the dimerization takes place more favorably for other polymers including poly(vinyl cinnamate). On the basis of the relationship between photoproduct distribution and liquid crystal photoalignment and on the reversibility of the photoinduced reorientation of a liquid crystal, it was concluded that the photoalignment results from the polarization photoisomerization of cinnamate residues in the same manner as that of photochromic moieties like azobenzenes, whereas the (2 + 2) photodimerization plays a role in enhancing the thermal stability of the homogeneous photoalignment.
TL;DR: The block copolymers in this article have been designed to have nearly identical molecular weight azobenzene-containing LC blocks in order to eliminate possible variations in LC behavior caused by the differences in the LC block molecular weight.
Abstract: The synthesis and characterization of a family of well-defined liquid crystal−coil (LC−coil) diblock copolymers have been carried out. The block copolymers in this study have been designed to have nearly identical molecular weight azobenzene-containing LC blocks in order to eliminate possible variations in LC behavior caused by the differences in the LC block molecular weight. Quantitative hydroboration chemistry was used to convert the pendent double bonds of an isoprene block to hydroxyl groups to which the mesogenic groups were attached via acid chloride coupling. The LC homopolymer and the block copolymers (LC volume fraction from fLC = 0.82 to fLC = 0.20) all exhibited smectic mesophases with similar clearing transition temperatures. The clearing transition enthalpies strongly depend on the block composition ratio and decrease as the LC block volume fraction decreases. Solvent-casting of a lamellar LC−coil copolymer (SICN5-66/60) resulted in an oriented bulk film in which both the axes of the mesogen...
TL;DR: In this article, a novel optical compensation film utilizing a negatively birefringent discotic compound was optimized by both simulation and experiment to achieve wide-viewing-angle characteristics of twisted-nematic liquid-crystal displays (TN-LCDs).
Abstract: The performance of a novel optical compensation film utilizing a negatively birefringent discotic compound was optimized by both simulation and experiment to achieve wide-viewing-angle characteristics of twisted-nematic liquid-crystal displays (TN-LCDs). It was shown that the film remarkably enlarges the viewing angle of TN-LCDs when the discotic compound layer has hybrid molecular orientation which is a similar structure to that of on-state liquid crystals of TN-LCDs.
TL;DR: It is shown that a monodisperse derivative of poly(γ-benzyl α,L-glutamate) prepared in this way shows smectic ordering in solution and in films, suggesting that methods for preparing monod isperse polymers might provide access to new smectics phases with layer spacings that are susceptible to precise control on the scale of tens of nanometres.
Abstract: Solutions and melts of stiff ('rod-like') macromolecules often exhibit nematic liquid crystalline phases characterized by orientational, but not positional, molecular order Smectic phases, in which macromolecular rods are organized into layers roughly perpendicular to the direction of molecular orientation, are rare, owing at least in part to the polydisperse nature (distribution of chain lengths) of polymers prepared by conventional polymerization processes Bacterial methods for polypeptide synthesis, in which artificial genes encoding the polymer are expressed in bacterial vectors, offer the opportunity to make macromolecules with very well defined chain lengths Here we show that a monodisperse derivative of poly(γ-benzyl α,L-glutamate) prepared in this way shows smectic ordering in solution and in films This result suggests that methods for preparing monodisperse polymers might provide access to new smectic phases with layer spacings that are susceptible to precise control on the scale of tens of nanometres
TL;DR: In this article, spontaneous formation of two types of helical structure was observed in two smectic phases consisting of banana-shaped achiral molecules for the first time, and local optical resolution occurs to form spatially resolved fingertips of both handednesses.
Abstract: Spontaneous formation of two types of helical structure is observed in
two smectic phases consisting of banana-shaped achiral molecules for the
first time. Local optical resolution occurs to form spatially resolved
helices of both handednesses.
TL;DR: In this article, a Monte Carlo algorithm is used to simulate the director field around a spherical inclusion in a uniform nematic liquid crystal matrix, and the resulting structure crucially depends on the relative strength of the nematic bulk elasticity and the director anchoring on the particle surface.
Abstract: We use a Monte Carlo algorithm to simulate the director field around a spherical inclusion in a uniform nematic liquid crystal matrix. The resulting structure crucially depends on the relative strength of the nematic bulk elasticity and the director anchoring on the particle surface. When this anchoring is weak, the director field perturbations are small and have quadrupolar symmetry. With increasing strength of anchoring two topologically nontrivial situations are possible: a dipolar configuration with a satellite point defect (hedgehog) near the particle pole, or a quadrupolar configuration with a ``Saturn ring'' of disclination around the particle equator.
TL;DR: In this article, a phase diagram of a water−poly(oxyethylene) oleyl ether (POlE) system was constructed as a function of poly(oxymethylene) chain length at 25 °C.
Abstract: A phase diagram of a water−poly(oxyethylene) oleyl ether (POlE) system was constructed as a function of poly(oxyethylene) chain length at 25 °C. The POlEs contain a highly pure oleyl group, whose purity is above 99.7%. The POlEs are in a liquid state over a wide range of composition. The increase in the poly(oxyethylene) (EO) chain of POlE corresponds to the increase in the curvature of surfactant layer toward water or the increase in HLB (hydrophile−lipophile balance) number of the surfactant. Various self-organizing structures were found: hexagonal and lamellar lquid crystals, four kinds of isotropic liquid crystals, a sponge phase, and reverse hexagonal liquid crystal. The phase transition between normal hexagonal and lamellar liquid crystals were investigated at constant volume fraction of the oleyl group in system by means of small-angle X-ray scattering. Correlation among the phase behavior, the packing of oleyl chain in self-organizing structures, and the HLB of POlE is discussed. The effect of te...
TL;DR: In this paper, the relationship between the conditions of phase separation, morphology, and electro-optic properties was explored and explained by consideration of the phase separation process, and confocal microscopy was shown to be a useful, noninvasive means of obtaining three-dimensional information on PDLC morphology.
Abstract: An attractive way of making polymer-dispersed liquid-crystal (PDLC) films is through photopolymerization-induced phase separation. The electro-optic properties of these films are determined in large part by the size, shape, and packing of the embedded liquid-crystal drops. We explore the relationships between the conditions of phase separation, morphology, and electro-optic properties. A strikingly strong dependence of electro-optic properties on the fraction of liquid crystal in the film is demonstrated and explained by consideration of the phase separation process. Also, confocal microscopy is shown to be a useful, noninvasive means of obtaining three-dimensional information on PDLC morphology. Not only does it provide very clear images of liquid crystalline drops in the film, but unexpected features were revealed. The drops exhibit a morphology much like a polyhedral foam in the films studied. Polymeric filaments inside the drops were observed as well as a drift in the average size of the drops with proximity to the film substrates. All of these features have important consequences for the electro-optic performance of PDLC films.
Patent•
21 Oct 1997
TL;DR: In this article, column-shaped spacers are disposed for controlling a gap between a pair of substrates, and each of the column shaped spacers has a portion for substantially controlling the gap between the pair of substrate and reflecting or absorbing visible light, which is located at an interface between the spacer and at least one of the substrates.
Abstract: The liquid crystal device of this invention includes a liquid crystal layer between a pair of substrates, wherein column-shaped spacers are disposed for controlling a gap between the pair of substrates, and each of the column-shaped spacers has a portion for substantially controlling the gap between the pair of substrates and a portion for reflecting or absorbing visible light, and the portion for reflecting or absorbing visible light is located at an interface between the spacer and at least one of the pair of substrates.
TL;DR: In this paper, the switching behavior of low-molecular-weight and polymer azobenzene liquid crystals (LCs) was explored by means of reflection-mode analysis.
Abstract: Optical switching behavior of low-molecular-weight and polymer azobenzene liquid crystals (LCs) was explored by means of reflection-mode analysis. Reflectivity changed on pulse irradiation under va...
Patent•
07 May 1997TL;DR: In this paper, the authors provided a model for polymer/cholesteric liquid crystal dispersions in which the liquid crystal phase separated from the polymer matrix to form droplets.
Abstract: Polymer/cholesteric liquid crystal dispersions are provided in which the liquid crystal phase separated from the polymer matrix to form droplets. The cholesteric liquid crystals were positive dielectric anisotropic. At a zero field condition, the liquid crystal in the droplets was bistable, that is, the liquid crystal can be in either the reflecting planar state or the scattering focal conic state. When the liquid crystal 101 was in the planar texture, the helical axis of the liquid crystal was more or less perpendicular to the cell surface; colored light 105 was Bragg reflected. When the liquid crystal 101 was in the focal conic texture, the helical axis was more or less parallel to the cell surface, incident light was scattering 106 in the forward direction.
TL;DR: These polymerization precursor structures suggest novel materials-design paradigms for gel LCs and nanophase-separated polymer systems.
Abstract: Photopolymerizable diacrylate monomers dissolved in fluid-layer smectic A and smectic C liquid crystal (LC) hosts exhibited significant spatial segregation and orientation that depend strongly on monomer structure. Small, flexible monomers such as 1,6-hexanediol diacrylate (HDDA) oriented parallel to the smectic layers and intercalated, whereas rod-shaped mesogen-like monomers such as 1,4-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)-2-methylbenzene (C6M) oriented normal to the smectic layers and collected within them. Such spatial segregation caused by the smectic layering dramatically enhanced photopolymerization rates; for HDDA, termination rates were reduced, whereas for C6M, both the termination and propagation rates were increased. These polymerization precursor structures suggest novel materials-design paradigms for gel LCs and nanophase-separated polymer systems.