Showing papers on "Liquid crystal published in 1999"
Book•
01 Jan 1999TL;DR: In this article, the authors present an introduction to liquid crystal technology and principles of operation of various modes of liquid crystal displays as well as the development of birefringent optical thin film technologies (e.g., polarizers, compensators) for improving the viewing quality of these displays.
Abstract: This tutorial covers an introduction to liquid crystal technology and principles of operation of various modes of liquid crystal displays as well as the development of birefringent optical thin film technologies (e.g., polarizers, compensators) for improving the viewing quality of these displays.
858 citations
839 citations
TL;DR: In this article, an optically birefringent nematic liquid crystal is infiltrated into the void regions of an inverse opal, photonic-band-gap (PBG) material, the resulting composite material exhibits a completely tunable PBG.
Abstract: We demonstrate that when an optically birefringent nematic liquid crystal is infiltrated into the void regions of an inverse opal, photonic-band-gap (PBG) material, the resulting composite material exhibits a completely tunable PBG. In particular, the three-dimensional PBG can be completely opened or closed by applying an electric field which rotates the axis of the nematic molecules relative to the inverse opal backbone. Tunable light localization effects may be realized by controlling the orientational disorder in the nematic.
718 citations
TL;DR: Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems.
Abstract: Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality.
643 citations
Book•
15 Jun 1999TL;DR: In this article, surface-stabilized ferroelectric liquid crystals were described, which caused a surge in industrial interest because of their promising electro-optical applications, in particular for high-resolution liquid crystal displays.
Abstract: Ferroelectric liquid crystals have been a major research topic since 30 years. However, when it comes to liquid crystals, the term “ferroelectric” is strongly ambiguous and frequently not only leads to confusion and misunderstanding but also obscures the basic concepts. The property of ferroelectricity in liquid crystals was first claimed in 1975. Five years later so-called surface-stabilized ferroelectric liquid crystals were described, which caused a surge in industrial interest because of their promising electro-optical applications, in particular for high-resolution liquid crystal displays. The industrial interest led to a considerable activity in synthesizing new compounds with the desired properties. In the course of this materials development antiferroelectricity in liquid crystals was then also sought for and was finally identified in 1989. At the same time as the first industrial ferroelectric devices (the Canon displays) came on the market in 1995, the antiferroelectric liquid crystals were bein...
476 citations
TL;DR: In this article, an organic EL device based on aligned con-jugated polymers which directly emitted polarized light was demonstrated, which would be particularly useful as backlights for conventional liquid crystal displays(LCDs).
Abstract: demonstrated an organic EL device based on aligned con-jugated polymers which directly emitted polarized light,and realized that such devices would be particularly usefulas backlights for conventional liquid crystal displays(LCDs). However, typical supertwisted nematic LCDs re-quire a contrast ratio of 40 to 50,
361 citations
TL;DR: In this article, the optical stop band in the transmission spectra of opals shifts drastically by the infiltration of liquid crystals and the stop band is also found to shift at the phase transition points with changing temperature.
Abstract: Nematic liquid crystals and smectic liquid crystals can be infiltrated into a three-dimensional periodic array of interconnected nanosize voids in opal films prepared by sedimentation of SiO2 spheres of various diameters. The optical stop band in the transmission spectra of opals shifts drastically by the infiltration of liquid crystals. The stop band is also found to shift at the phase transition points with changing temperature. This effect enables the tuning of optical properties of opals as a prototype tunable photonic crystal. This phenomenon can also be used as a measurement method for the refractive index.
324 citations
Book•
01 Apr 1999
TL;DR: In this paper, the basic physical properties of liquid crystal materials, including the structure and symmetry of Liquid Crystal Phases, the temperature range and phase transitions, and the cell preparation, are discussed.
Abstract: Liquid Crystals -- Basic Physical Properties: Structure and Symmetry of Liquid Crystal Phases LC Mixtures, the Temperature Range and Phase Transitions Basic Physical Properties Surface Phenomena and Cell Preparation New Basic Developments in Liquid Crystals Electrooptical Effects in Liquid Crystal Materials: Electrically Controlled Birefringence Twist-Effect Supertwist Effects Bistable Effects 'Guest-Host Effect' Electrooptical Properties of Polymer Dispersed Liquid Crystal Films Electrooptic Effects in Ferroelectric and Antiferroelectric Liquid Crystals Recent Developments of Electrooptical Modes for LCD Applications Liquid Crystal Displays: Liquid Crystal Displays Among the Other Types of Flat Panel Displays Active - Matrix Addressing LCDs Other LCD Types Recent Advances in LCDs and Competing Technologies Non-Display Applications of Liquid Crystals: Liquid Crystals in Optical Data Processing Systems Other Non-Display Applications of Liquid Crystals Novel Non-Display LC Devices Appendices
312 citations
TL;DR: In this article, the authors reported the generation of strongly circularly polarized photoluminescence from films of glass-forming chiral-nematic liquid crystals in which are embedded light-emitting dopants.
Abstract: Optical information processing, display and storage can be accomplished with linearly or circularly polarized light. In passive (non-emitting) devices, linear polarization can be produced by anisotropic absorption of light1, whereas circular polarization has been attained by selective reflection of unpolarized light propagating through a chiral-nematic liquid-crystal film2. Active (light-emitting) devices capable of polarized emission are also needed. In principle, optical and electronic excitation of materials containing uniaxially and helically arranged luminophores should produce linearly and circularly polarized emission, respectively. In practice, the former is easier to achieve and is therefore more technologically advanced3,4,5,6,7,8. Here we report the generation of strongly circularly polarized photoluminescence from films of glass-forming chiral-nematic liquid crystals9 in which are embedded light-emitting dopants. This host material apparently induced alignment of the luminophores to a degree that produces almost pure circular polarization within the 400–420-nm wavelength band of the emitted light. We anticipate that composite films of this sort might find applications within photonic technology such as colour-image projection10 and stereoscopic displays11.
303 citations
TL;DR: In this paper, the authors show that a more than one order of magnitude increase in time-of-flight hole mobility normal to the alignment direction occurs when poly(9,9′-dioctylfluorene) films are aligned with rubbed polyimide.
Abstract: Homogeneous alignment of poly(9,9′-dioctylfluorene) films on rubbed polyimide results in a more than one order of magnitude increase in time-of-flight hole mobility normal to the alignment direction. We find μ=8.5±1×10−3 cm2/V s at an electric field of E=104 V/cm. Hole transport is found to be nondispersive, indicating a low degree of energetic disorder.
264 citations
01 Mar 1999
TL;DR: In this paper, a comprehensive description of the mechanical equilibrium and deformation of membranes as a surface problem in differential geometry is presented, and the results of the investigation into the solution of the equation that have been carried out by the authors.
Abstract: Contains a comprehensive description of the mechanical equilibrium and deformation of membranes as a surface problem in differential geometry. Following the pioneering work by W. Helfrich, the fluid membrane is seen as a nematic or smectic - a liquid crystal film and its elastic enegy form is deduced exactly from the curvature elastic theory of the liquid crystals. With surface variation, the minimization of the energy at the fixed osmotical pressure and surface tension gives a surface equation in geometry that involves potential interest in mathematics. This text presents the results of the investigation into the solution of the equation that have been carried out by the authors.
TL;DR: In this article, a superlattice structure in which a mineral continuum was featured with hexagonally arranged cylindrical pores 2−3 nm in diameter and 5 nm apart was found to be thermodynamically stable.
Abstract: Various nanoscale semiconducting superlattices have been generated by direct templating in a lyotropic organic liquid crystal. These include superlattices of CdS, CdSe, and ZnS, templated in a liquid crystal formed by oligoethylene oxide oleyl ether amphiphiles and water. The semiconductor growth process copied the symmetry and characteristic dimensions of the original mesophase by avoiding growth of mineral within regularly spaced hydrophobic regions. The final product was a superlattice structure in which a mineral continuum was featured with hexagonally arranged cylindrical pores 2−3 nm in diameter and 5 nm apart. Most importantly, the superlattice morphology of the nanostructured systems in contact with the mesophase was found to be thermodynamically stable with respect to the solid lacking nanoscale features. We also found that both the morphology of features in the nanostructured solids and their dimension can be controlled through the amphiphile's molecular structure and water content in the liquid...
TL;DR: In this paper, inorganic films with a porous structure engineered on the submicrometre scale by glancing-angle deposition were used to control the orientation of liquid crystals impregnated into the voids.
Abstract: Control over the orientational order of liquid crystals (LCs) is critical to optical switching and display applications. Porous polymer networks have been used to influence the orientation of embedded chiral liquid crystals1, yielding for example reflective displays. Here we show that inorganic films with a porous structure engineered on the submicrometre scale by glancing-angle deposition2,3 can be used to control the orientation of LCs impregnated into the voids. The inorganic material contains helical columns that orient rod-like nematic LCs into a phase similar to a chiral nematic1,4 but with direct control of the local molecular arrangement (for example, the helical pitch) imposed by the inorganic microstructure. We also show that reactive LC molecules in this composite material can be crosslinked by photopolymerization while retaining the imposed structure.
TL;DR: This system serves as a model for a class of solids formed when particles are mixed with layered materials such as thermotropic and lyotropic smectic liquid crystals and block copolymers.
Abstract: Dispersions of colloidal particles in cholesteric liquid crystals form an unusual solid by stabilizing a network of linear defects under tension in the ideal layered structure of the cholesteric. The large length scales of the cholesteric liquid crystals allowed direct observation of the network structure, and its properties were correlated with rheological measurements of elasticity. This system serves as a model for a class of solids formed when particles are mixed with layered materials such as thermotropic and lyotropic smectic liquid crystals and block copolymers.
TL;DR: In this article, a detailed computer simulation study of Gay-Berne particles interacting via a potential parametrized to reflect the anisotropic forces based on a fit to a realistic mesogenic molecule is presented.
Abstract: The Gay–Berne potential is proving to be a valuable model with which to investigate the behavior of liquid crystals using computer simulation techniques. The potential contains four independent parameters which control the anisotropy in the attractive and repulsive interactions. The choice of these parameters is not straightforward and it would seem that those employed in some simulations are not strictly appropriate for mesogenic rodlike molecules. Here we report a detailed computer simulation study of Gay–Berne particles interacting via a potential parametrized to reflect the anisotropic forces based on a fit to a realistic mesogenic molecule. The behavior of the phases and the transitions between them have been investigated for a system of 2000 particles using isothermal–isobaric Monte Carlo simulations. At low pressures, this Gay–Berne mesogen exhibits isotropic, smectic A and smectic B phases but, as the pressure is increased, so a nematic phase is added to the sequence. The nature of the phase transitions and the phase diagram are compared where possible with those of real mesogens. The structures of the four phases have been investigated in detail for a larger system of 16 000 particles using canonical molecular dynamics simulations at state points taken from the phase diagram determined from the Monte Carlo simulations. A wide range of singlet and pair distribution functions were evaluated together with orientational correlation coefficients and, for the smectic phases, a bond orientation correlation function. The results for these properties were used to identify the phases, to consider their structure at a quantitative level and, where possible, to make contact with experimental studies and the predictions of theories of liquid crystals. It would appear that with this parametrization, the Gay–Berne potential provides a powerful tool with which to understand the behavior of real liquid crystals and to test the predictions of theory.
TL;DR: Results of a simulation of control signals that have a range of harmonics that are switchable lenses with a continuous phase variation across the lens and experimental results showing a liquid crystal lens varying its focal length are presented.
Abstract: Liquid crystal modal lenses are switchable lenses with a continuous phase variation across the lens. A critical issue for such lenses is the minimization of phase aberrations. In this paper we present results of a simulation of control signals that have a range of harmonics. Experimental results using optimal sinusoidal and rectangular voltages are presented. A lack of uniqueness in the specification of the control voltage parameters is explained. The influence of a variable duty cycle of the control voltage on an adaptive lens is investigated. Finally we present experimental results showing a liquid crystal lens varying its focal length.
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01 Jan 1999
TL;DR: The Physicochemistry of Surfactants as mentioned in this paper The Physicochemical properties of solvers of polymers are discussed in detail in Section 5.1.3.1 and Section 6.2.
Abstract: 1. Droplets: Capillarity and Wetting.- 2. Fractals.- 3. Small Volumes and Large Surfaces: The World of Colloids.- 4. The Physicochemistry of Surfactants.- 5. From Giant Micelles to Fluid Membranes: Polymorphism in Dilute Solutions of Surfactant Molecules.- 6. Polymers Formed from Self-Assembled Structures.- 7. Polymer Materials.- 8. Polymer Solutions: A Geometric Introduction.- 9. Liquid Crystals: Between Order and Disorder.
TL;DR: A comprehensive overview of the relationships between molecular structure and liquid crystallinity in dimers is provided in this article, including a description of the novel modulated and intercalated smectic phases exhibited by dimers.
Abstract: A liquid crystal dimer is composed of molecules containing two conventional mesogenic groups linked via a flexible spacer. These materials show quite different behaviour to conventional low molar mass liquid crystals and in particular their transitional behaviour exhibits a dramatic dependence on the length and parity of the flexible spacer. In this review a comprehensive overview of the relationships between molecular structure and liquid crystallinity in dimers is provided. This includes a description of the novel modulated and intercalated smectic phases exhibited by dimers.
IBM1
TL;DR: In this article, the microscopic origin of the alignment of a nematic liquid crystal (LC) when placed on a rubbed polymer surface was discussed and the experimental results were explained by a general theory, based on tensor order parameters, which states that the minimum energy state of the interaction between the LC and oriented polymer surface corresponds to maximum directional overlap of the respective anisotropic charge distributions.
TL;DR: A stabilization of the liquid- Crystalline mesophase and thus an enlarged temperature range of the mesogenic phase is achieved by adding perfluorotriphenylene to a chiral liquid-crystalline triphenylene.
Abstract: A stabilization of the liquid-crystalline mesophase and thus an enlarged temperature range of the mesogenic phase is achieved by adding perfluorotriphenylene to a chiral liquid-crystalline triphenylene. This mesophase is based on 1:1 perfluoroarene-arene interactions (see picture). In a polymer with triphenylenes as mesogens in the side chains, the addition of perfluorotriphenylene led to crystallization.
TL;DR: In this paper, the structure of the spider's silk production pathway and the liquid crystalline feedstock are both involved in defining the exceptional mechanical properties of spider dragline silk, and the behavior of droplet inclusions within the silk feedstock indicated that elongational flow at a low shear rate occurs in the gland's duct and may be important in producing an axial molecular orientation before the final thread is drawn.
Abstract: Our observations on whole mounted major ampullate silk glands suggested that the thread is drawn from a hyperbolic die using a pre–orientated lyotropic liquid crystalline feedstock. Polarizing microscopy of the gland's duct revealed two liquid crystalline optical textures: a curved pattern in the feedstock within the ampulla of the gland and, later in the secretory pathway, the cellular texture previously identified in synthetic nematic liquid crystals. The behaviour of droplet inclusions within the silk feedstock indicated that elongational flow at a low shear rate occurs in the gland's duct and may be important in producing an axial molecular orientation before the final thread is drawn. Our observations suggested that the structure of the spider's silk production pathway and the liquid crystalline feedstock are both involved in defining the exceptional mechanical properties of spider dragline silk.
TL;DR: 15N-1H dipolar couplings measured for ubiquitin over the 2.3–10.4pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.
Abstract: It is demonstrated that mixtures of ditetradecyl-phosphatidylcholine or didodecyl-phoshatidylcholine and dihexyl-phosphatidylcholine in water from lyotropic liquid crystalline phases under similar conditions as previously reported for bicelles consisting of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl-phosphatidylcholine (DHPC). The carboxy-ester bonds present in DMPC and DHPC are replaced by ether linkages in their alkyl analogs, which prevents acid- or base-catalyzed hydrolysis of these compounds. 15N-1H dipolar couplings measured for ubiquitin over the 2.3-10.4 pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.
TL;DR: In this paper, the effect of metastability and the occurrence of hysteresis in connection with a magnetic field on the spin transition from the dipole to the Saturn ring configuration is discussed.
Abstract: We study the director field around a spherical particle immersed in a uniformly aligned nematic liquid crystal and assume that the molecules prefer a homeotropic orientation at the surface of the particle. Three structures are possible: a dipole, a Saturn-ring, and a surface-ring configuration, which we investigate by numerically minimizing the Frank free energy supplemented by a magnetic-field and a surface term. In the dipole configuration, which is the absolutely stable structure for micron-size particles and sufficiently strong surface anchoring, a twist transition is found and analyzed. We show that a transition from the dipole to the Saturn ring configuration is induced by either decreasing the particle size or by applying a magnetic field. The effect of metastability and the occurrence of hysteresis in connection with a magnetic field are discussed. The surface-ring configuration appears when the surface-anchoring strength W is reduced. It is also favored by a large saddle-splay constant K24. A comparison with recent experiments [#!itapdb:Poulin1997!#,#!itapdb:Poulin1998!#] gives a lower bound for W, i.e., W >0.06erg/cm2for the interface of water and pentylcyanobiphenyl (5CB) in the presence of the surfactant sodium dodecyl sulfate.
TL;DR: In this article, a free energy expression for a mixture of polymers and solid, thin disks is derived from the Onsager model for the equilibrium behavior of rigid rods, which takes into account the possible nematic ordering of the disks within the polymer matrix.
Abstract: To model the phase behavior of polymer−clay composites, we develop a free energy expression for a mixture of polymers and solid, thin disks. The free energy expression is adopted from the Onsager model for the equilibrium behavior of rigid rods. Thus, our theory takes into account the possible nematic ordering of the disks within the polymer matrix. By minimizing this free energy and calculating the chemical potentials, we construct phase diagrams for the polymer−disk mixtures. The findings provide guidelines for tailoring the polymer molecular weight and the volume fraction of the different components to fabricate thermodynamically stable mixtures with the desired morphology.
TL;DR: This method makes it possible to prepare devices with liquid crystal film thickness comparable to optical wavelengths, and exhibits electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer-stabilization methods.
Abstract: A method of preparing liquid crystal devices by phase separation of liquid crystal from its solution in a prepolymer, which results in adjacent layers of liquid crystal and polymer, is described. Liquid crystals in these phase-separated composite films exhibit electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer-stabilization methods. Devices incorporating ferroelectric liquid crystals have gray scale and switch 100 times faster at low fields than conventional surface-stabilized devices. This method makes it possible to prepare devices with liquid crystal film thickness comparable to optical wavelengths.
TL;DR: In this article, the authors describe recent studies and research effort concerning the liquid crystalline behavior of compounds incorporating a highly fluorinated part with more than one fluoromethylene units and examine some of their mesophase properties and the impact of molecular shape on the resulting liquid crystal behavior.
TL;DR: In this article, the defect modes of cholesteric liquid crystals as photonic band gap materials were investigated and the wavelength and reflectivity of defect modes were analyzed in terms of the refractive index of defect layer.
Abstract: We investigate defect modes of cholesteric liquid crystals as photonic band gap materials. For normal incidence of light, cholesteric liquid crystals exhibit total reflection for the circular polarization with the same handedness as that of cholesteric helix. However, the other orthogonal component is completely transmitted. When we replace a thin layer of liquid crystal by an isotropic material as a defect, defect modes are induced for both polarizations of incident light. We analyze the wavelength and reflectivity of the defect modes in terms of the refractive index of defect layer. @S1063-651X~99!09312-5#
TL;DR: In this paper, the authors refined the united atom field for the simulations of phospholipid membranes and performed 1000-ps constant pressure simulation of a dipalmitoylphosphatidicholine (DPPC) bilayer at T = 50° C.
Abstract: We refined the united atom field for the simulations of phospholipid membranes. To validate this potential we performed 1000-ps constant pressure simulation of a dipalmitoylphosphatidicholine (DPPC) bilayer at T=50° C. The average area per head group (61.6±0.6) A2 obtained in our simulation agrees well with the measured one of (62.9±1.3) A2. The calculated SCD order parameters for the Sn-2 hydrocarbon tail also display a good agreement with the experiment. The conformations of head groups in our simulations of the liquid crystal phase are different than the ones observed in the crystal structure. ©1999 John Wiley & Sons, Inc. J Comput Chem 20, 531–545, 1999