Liquid Crystal Configurations Research Articles

1C09 球状粒子のまわりのネマチック液晶の配向に対する流れ場の影響(物理・物性)

1C09 球状粒子のまわりのネマチック液晶の配向に対する流れ場の影響(物理・物性)

P‐108: Robust Polymer Stabilization for Cholesteric Liquid Crystal Reflective Displays

AbstractWe have developed a robust way to stabilize cholesteric liquid crystal materials for reflective display applications. Using a photolithographic‐type exposure process we enclose cholesteric liquid crystal in cylindrical containers to create a film that is extremely robust for flexible and conformable display applications. We discuss the influence of cylindrical containment on the cholesteric liquid crystal configuration and its influence on the electro‐optic properties.

Suspension polymerization of thermotropic monomer: Formation of droplets or beads

Ordered beads were obtained by the suspension copolymerization of amesogenic methacrylate-based monomer and methacrylic acid. The stability of these particles and the liquid crystal organization inside the particles depend mainly on the time of polymerization and on the crosslinking. Suspended droplets of monomers or polymers can be obtained as well as solid spheres. The solid particles exhibit ordered microstructures with a liquid crystal configuration that has a variable form depending on polymerization time and observation temperature. Bead characteristics such as morphology, size and polydispersity, and porosity are discussed and compared with those of non-mesomorphic beads. The mesomorphic beads are smaller and their porosity lower. The presence of a crosslinker during the polymerization process leads to more mechanically stable particles with retention of polymorphism.

MODELLING MULTI-DIMENSIONAL OPTICS IN COMPLEX LIQUID CRYSTAL STRUCTURES AND DISPLAYS

Finite Difference Time Domain (FDTD) numerical modelling of light scattering from complex structures in liquid crystals is undertaken. As an example, typical Polymer Dispersed Liquid Crystal (PDLC) configurations such as the radial, axial, bipolar and concentric structures are analysed. Two-dimensional studies are used together with Gaussian Beam illumination conditions. In addition, the scattering at the edge of an isolated twisted nematic pixel in a reflective device is modelled. Apart from the numerical discretisation, no other approximations are introduced.

Chain length dependence of confined liquid crystals configuration

The study of confined liquid crystals flourished in the decade of the nineties. Liquid crystals properties have been probed after confinement in well‐defined or interconnected geometries as those available in porous media and in polymer networks. In this work we emphasized the power of the nuclear magnetic resonance technique to determine the confined liquid crystal structures. We also present unexpected results on the dependence of the confined liquid crystal configuration on the chain length.

23.4: Development of Authentic‐Color IPS LCD without Color Trackin

AbstractColor tracking in an LCD, which is defined as chromaticity dependence on brightness, is analyzed in terms of the director configuration of liquid crystal with voltage. We have developed an Authentic‐color IPS, using an optimized backlight and a lower retardation panel, which can avoid color tracking. The chromaticity difference between black and white representation is below the limit of perception.

Long Term Bistable Twisted Nematic Liquid Crystal Display and Its Computer Simulations

The multidimensional alignment (MDA) technique realized by the polymer wall has been previously proposed as a means to stabilize the liquid crystal configurations for twist angles of 0 and 2π so that very low power and real bistable twisted nematic (BTN) liquid crystal display (LCD) can be obtained. In this study, a two-dimensional liquid crystal director simulation software was employed to explore the stability of BTN devices. The simulation results showed that the homeotropic aligned polymer wall will stabilize the BTN device when the ratio of d/p is close to the switching d/p ratio, but when the d/p ratio is higher than 0.9, the director field will convert the configuration from a high-energy 0 twist state to low-energy 2π twist state automatically, therefore the BTN bistability will be destroyed.

P‐79: Model of Freedericksz Transition and Hysteresis Effect in Polymer Stabilized Nematic Liquid Crystal Configurations for Display Applications

AbstractThe critical field of the Freedericksz transition and optical hysteresis is investigated for Polymer Stabilized Nematic Liquid Crystals as a function of polymer concentration. The results are described by a simple phenomenological model, which accounts for the change in polymer network morphology as the concentration of polymer is increased.

On the stability of two nematic liquid crystal configurations

In this article we study the stability properties of two different configurations in nematic liquid crystals. One of them is the static configuration in the presence of magnetic fields. The other one is the Poiseuille flow under the model of Ericksen for liquid crystals with variable degree of orientation [E, 91]. In the first case, we show that the planar radial symmetry solution is stable with respect to the small external magnetic field. Such phenomenon illustrates the competition mechanism between the magnetic field and the strong anchoring boundary conditions. In the Poiseuille flow case, we show that the stationary configuration obtained from our previous works [C-L, 99] [C-M, 96] is stable when the velocity gradient is small.

A New Design of Optical Configuration of Transflective Liquid Crystal Displays using Antiferroelectric Liquid Crystals and Frustelectric Ferroelectric Liquid Crystals

We propose an optical configuration of transflective antiferroelectric liquid crystal (AFLC) and frustelectric ferroelectric liquid crystal (FR-FLC) display modes using a half-wave LC cell in which the in-plane tilt angle is 22.5°. It is composed of two polarizers, an AFLC or FR-FLC cell, two achromatic quarter-wave films, and a transflective film layer. In the case of using it in the reflective mode, it provides a high brightness and a high contrast ratio, and in the case of using it in the transmissive mode, it also provides a high contrast ratio. By fabricating modes of a transflective liquid crystal display (LCD) with a half-wave retardation, we demonstrated high brightness as well as high contrast ratio of a half-wave by the commercial simulator (DIMOS).

3D02 球状粒子のまわりのネマチック液晶の配向: adaptive mesh refinement を用いた数値解析

3D02 球状粒子のまわりのネマチック液晶の配向: adaptive mesh refinement を用いた数値解析

Smectic A liquid crystal configurations with interface defects

AbstractWe study planar energy minimizing configurations of smectic A liquid crystal materials and classify the corresponding defect structures. We investigate focal conic configurations in wedge, non‐parallel plates, funnel‐shaped domains, and non‐concentric annuli. The application of the stability condition for focal conics is relevant to the specification of the location of the interfacial defects. Self‐similar structures are discussed for a class of solutions with the same bulk energy. We propose surface energies terms to serve as selection mechanisms of particular self‐similar configurations. We also show how the modelling of chevron texture naturally arises in the present framework. Copyright © 2001 John Wiley & Sons, Ltd.

Director configuration and dynamics of a nematic liquid crystal around a two-dimensional spherical particle: Numerical analysis using adaptive grids

We study numerically the director and orientational order parameter configurations in a nematic liquid crystal around a two-dimensional spherical particle on the basis of the tensor order parameter formalism. To properly account for the large length scale difference between the particle and the accompanying orientational defect, we devise an adaptive grid scheme in which the lattice spacing is automatically and locally adjusted in response to the spatial gradient of the orientational order parameter. This adaptive grid scheme is useful in studying dynamical as well as static orientational structures. We present a simulation result which shows how a hedgehog defect of topological charge -1 becomes unstable in two dimensions, and splits into a defect pair of topological charge -1/2, located symmetrically around the particle.

Twist-energy-driven helfrich modulations in cholesteric liquid crystals illustrated in the transient-planar to planar transition

The complete time evolution of a Helfrich-type instability that is driven by twist energy in a cholesteric liquid crystal is presented. The modulation is investigated using an initially uniform planar director configuration of a cholesteric liquid crystal (with helical axes uniformly aligned along the cell normal) whose pitch is substantially longer than the equilibrium value.

Mathematical developments in the study of smectic A liquid crystals

We consider free energy functionals to model equilibrium smectic A liquid crystal configurations in the neighborhood of the nematic phase transition. We first look at the functional proposed by de Gennes based on the Ginzburg–Landau model for superconductivity, and consider its covariant formulations. We construct the focal conic solution and study its stability. We also study the role of chirality in the model of smectic A *. In the final part of the paper, we use an argument of symmetry breaking to model smectic phases as periodic solutions of an extend nematic theory.

Numerical analysis of nematic liquid crystal alignment on asymmetric surface grating structures

The influence of an asymmetric periodic grooved cell surface on the 2D static director configuration of a nematic liquid crystal has been investigated. The minimum in the Frank-Oseen free energy was solved numerically with the Rapini-Papoular form of the surface anchoring energy at the nematic-grating interface. Results are presented for the variation of pretilt angle in the tilted bulk director field as a function of the surface groove depth, pitch and asymmetry and the bulk parameters. The simulations demonstrate the existence of two energetically degenerate high and low pretilted bulk alignment configurations. The pretilt values in these two regimes and also for the low tilt regime with finite surface anchoring are consistent with experimental results. An effective increase in the resolution of the model is obtained by using an irregular grid to describe the surface profile.

Ericksen's Bar and Modeling of the Smectic A--Nematic Phase Transition

We consider free energy functionals to model equilibrium smectic A liquid crystal configurations in the neighborhood of the nematic phase transition. We begin with the functional proposed by de Gennes based on the Ginzburg--Landau model for superconductivity and consider its covariant formulations. Exploring qualitative analogies with the nonlinear elastic bar of Ericksen, we motivate a revision of the liquid crystal energy so as to include a nonconvex constraint. We study boundary-value problems corresponding to Neumann and Dirichlet boundary conditions for smectic A liquid crystals confined between two parallel plates. We show that the nonconvex term of the free energy density causes the presence in the solutions of nematic defects known to occur near the phase transition from smectic A to nematic. The latter are reminiscent of the dislocations occurring in higher dimensional configurations. We also determine parameter values that give rise to nucleation of nematic defects for boundary conditions consistent with externally imposed winding of the smectic phase field. The resulting energy also allows us to sort out liquid-like and solid-like behaviors, respectively.

Light Absorption Properties of Anthraquinone Dyes and Guest-Host Liquid Crystal Displays

ABSTRACTThe light absorption properties of anthraquinone dye in different hosts are compared in order to demonstrate the influence of the dye-liquid crystal interactions on dye order parameter. Surprisingly, the anthraquinone dye have a higher order parameter in liquid crystalline mixtures of positive dielectric anisotropy as well as in a liquid crystalline mixture of negative dielectric anisotropy (S = 0.71-0.82). We studied the Heilmeier displays use homogeneous alignment. The display is operated at the reverse mode, transparent at zero field. The switching voltage between the bright and dark states for these displays is 2-4 volts, depending on host liquid crystal and cell configuration.

Computation of a Few Small Eigenvalues of a Large Matrix with Application to Liquid Crystal Modeling

Equilibrium configurations of liquid crystals in a finite containment are minimizers of the thermodynamic free energy of the system. It is important to be able to track an equilibrium configuration as the temperature of the liquid crystals is decreased. The path of the minimal energy configuration at a bifurcation point can be computed from the null space of a sparse symmetric matrix, which typically is very large, e.g., of order 3 × 105. We describe an implicitly restarted block Lanczos method designed for the computation of a few extreme multiple or close eigenvalues and associated eigenvectors of a large sparse symmetric matrix and apply this method to determine the desired null space. Our method generalizes the implicitly restarted Lanczos method introduced by Sorensen. The method requires that certain acceleration parameters, referred to as shifts, be chosen. The storage requirement depends on the choice of shifts. We propose a new strategy for choosing shifts. Numerical examples illustrate that the implicitly restarted block Lanczos method with shifts chosen in this manner gives rapid convergence, reliably detects extreme multiple or close eigenvalues, and requires little computer storage in addition to the storage used for the desired eigenvectors. These features make the method well suited for the application of tracking an equilibrium configuration of liquid crystals.

New ferroelectric displays and operation modes

We first review ferroelectric displays and novel operating modes recently developed in our laboratories and elsewhere. The displays include deformed helix ferroelectric (DHF)-LCDs in large-cell-gap configurations as well as double-layer LCDs in transmission and reflection combined with fixed or switched optical compensators. These configurations are applicable to all electro-optic effects which are based on the rotation of the optical axis in the plane of the device, e.g. surface stabilized, electroclinic, flexoelectro-optic or DHF-LCDs. Moreover, a new ferroelectric display is presented which we denominate Alternating Polarization Domain (APD)-display. The new display is based on a low-Ps ferroelectric liquid crystal configuration which spontaneously aligns such that very narrow parallel stripes with opposite direction of spontaneous polarization are generated in the plane of the display. The alignment does not require field-induced texture formation. APD-LCDs are shown to exhibit low driving voltages (2 volts), gray scale and short response times (300 μs). In combination with optical compensators active-matrix driven reflective APD_LCD-projectors with driving voltages of 5V are possible.