Advanced electro-optic properties of nematic liquid crystal doped with high birefringence liquid crystal molecules

The study of fast response nematic liquid crystal display material mixture and synthesis about compounds has always been an important subject in recent years. In this article, one type of high birefringence liquid crystal based on phenyl-diacetylenes was synthesized by sonogashira coupling reaction. A research is conducted on the effect of electro-optic properties of a widely used nematic liquid crystal mixture doped with the prepared high birefringence liquid crystal molecule which concentrations ranging from 1% to 5 wt%. While the results show that the steepness of electro-optic curves first increase and then decrease with the prepared high birefringence liquid crystal molecule content increasing, when the content of high birefringence liquid crystal molecule reaches 3%, electro-optic properties of the mixture liquid crystals are excellent.     

晶体生长时的固液相结构变化分析

晶体的溶解、熔化以及结晶成核生长时的固液相原子结构是怎样变化的,晶体生长时的生长基元是原子还是原子团.本文根据各种材料液相结构的最新研究结果,提出不饱和配位结构转换模式,并以此模式对各种常见晶体材料从溶解、熔化到结晶生长时的液态母相结构变化以及晶体成核过程进行了描述和分析,认为晶体生长时的界面结构和液相结构十分接近,溶解、熔化主要是晶体表面的不饱和配位原子(离子)转换到液相结构的过程,晶体生长主要是液相中的不饱和配位原子(离子)转换到固液生长界面的位错位置,使配位结构更饱和的过程.随着液相过饱和度的增大,液相结构单元的原子数越来越多,吸附到晶体生长界面若来不及转换回液相,就形成新的位错生长中心,形成晶体生长缺陷.     

Behaviour of Nematic Liquid Crystals in Inhomogeneous Electric Fields

The behaviour of homogeneously aligned nematic liquid crystal layers in inhomogeneous electric fields has been theoretically and experimentally investigated. The variation of the phase retardation of monochromatic light along nematic liquid crystal layer at the edges of a cell electrode has been obtained. Anisotropic character of the resolution of liquid crystal devices is shown.     

Birefringence of binary liquid crystalline mixtures of MBBA and PPMAECOBA in TCM,interferometric assessment

Abstract

The mutual influence of two mesogenic components, namely a nematic liquid crystal N-(p-methoxy-bezylidene)-butylaniline (MBBA) and a lyotropic liquid crystal poly-(phenyl-methacrylic) ester of cetyloxybenzoic acid (PPMAECOBA) in tetra-chloromethane (TCM) is studied in this paper. The ordinary and extraordinary refractive indices of the mixtures, nematic liquid crystal and lyotropic liquid crystal were measured at 589.3?nm with a Rayleigh interferometer and some electro-optical parameters were computed. The main refractive indices, the birefringence, the main normalized polarizabilities and their difference are dependent on the mixture volumetric concentrations, proving the existence of the collective orientational interactions between the two types of liquid crystals.     

Study of Formation,Phase Behavior,and Microdroplet Size of a Polyurethane-based Polymer-dispersed Liquid Crystal

Using calorimetry and scanning electron microscopy, we have investigated the formation process and phase behavior of a polyurethane-based polymer-dispersed liquid crystal system. We have measured the kinetics and energetics of the cure process during which liquid crystal microdroplets form by phase separation from the matrix as it cross-links. The greatest degree of cure occurs for samples cured at 375 K. For a given cure temperature, the heat of cure decreases more or less linearly with increasing liquid crystal concentration due to a dilution effect. The time constant for the cure process decreases rapidly with increasing temperature but is much less sensitive to liquid crystal content.

Samples cured below 375 K are apparently not fully phase separated, but subsequent treatment at higher temperatures evidently increases the degree of cure. The highest nematic-isotropic transition temperatures were achieved for liquid crystal concentrations above 40 volume percent. The nematic isotropic transition enthalpy, ΔH_NI, is a measure of the amount of liquid crystal contained in the microdroplets. A model has been developed which explains the linear increase of ΔH_NI with increasing liquid crystal concentration.

Optimum microdroplet formation occurs at 375 K, but only for liquid crystal concentrations below about 53 volume percent. At higher concentrations a reversed phase (“polymer ball”) morphology is seen. For the lower concentrations droplet size increases linearly with LC content. Droplet number density decreases with increasing droplet size in rough agreement with a simple model.     

Tunable Optofluidic Polymer Photonic Liquid Crystal Fibers

New trends are presented in optofluidics based on microstructured photonic crystal fibers filled with liquid crystals. It significantly enhanced optical properties of the fibers and introduced new levels of tunability to photonic crystal fibers. The paper discusses basic research directions in fiber-based optofluidics and, in particular, in polycarbonate-based photonic liquid crystal fibers. Experimental and theoretical results are presented on polymer crystal fibers filled with nematic liquid crystal with two different types of dielectric anisotropies.     

Oriented action of some solid substrates to liquid crystal layer

The orienting action of three types of layers on liquid crystal is investigated. Homogeneous orientation of the liquid crystal layer is obtained under the action of a transparent conductive SnO₂ film and carbon film. Such an orientation is achieved with gelatin films as well. Homeotropic orientation of the liquid crystal can be also obtained by exposing the latter to ion bombardment with Ar ions.     

Nanostructures on the Basis of Porous Alumina with Intercalated with Cholesteric Liquid Crystal

The introduction of liquid crystal materials into the porous material host will help us to get optically active nanocomposites. Nanocomposite based on aluminum oxide host with cholesteric liquid crystal is characterized by a shift of bandwidth wavelength minimum. In case of intercalation of cholesteric liquid crystals into the pores of aluminum oxide host the shift of transmittance minimum into the short wave region are observed. We analyzed the ways, which indicate the deformation of the pitch of the cholesteric helix and showed the role of capillary forces in the deformation of the pitch of cholesteric liquid crystal.     

Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly(methyl methacrylate)

Polymer dispersed liquid crystal composite films were prepared from poly(methyl methacrylate) and nematic liquid crystal E44 by solvent induced phase separation method. In the present investigation we report effect of liquid crystal concentration on the electro-optical and dielectric properties of the composite films. The results were interpreted in terms of phase separation of liquid crystal and polymer, shape and size of liquid crystal droplet, interfacial charge layer effect, liquid crystal loading and miscibility of liquid crystal in the polymer matrix. The miscibility between two phases at interface was investigated by employing Fourier‐Transform Infrared Spectroscopy and differential scanning calorimetry. Morphological study showed that liquid crystal phase is embedded in a spongy poly(methyl methacrylate) matrix and homogeneous distribution increased with increasing E44 content. Electro optical behavior of these composite films under the condition of an externally applied AC electric field (0–200 Vp-p, 50–1000 Hz) and wide range of temperature was determined using He–Ne laser (wave length 632.8 nm) as a light source. It was found that Poly(methyl methacrylate)/E44 (30/70) wt.% composite has more significant properties than the other concentrations. The performance of all composites showed variations with respect to applied voltage as well as temperatures. Dielectric measurement of polymer dispersed liquid crystals has been carried out in the frequency range from 20 Hz to 20 MHz and over the temperature range from 24 °C to 100 °C. The Maxwell–Wagner effect due to interfacial charge accumulation between boundaries of liquid crystal droplets and surrounding of polymer matrix has been observed.     

Formation of the Liquid Crystal of a Surface-active Dye in Aqueous Methanol Solutions

The formation of the liquid crystal phase of a surface-active dye, p-octylphenol yellow amine poly(ethylene oxide), in aqueous methanol solutions has been examined by optical microscopy. Rodlike swarms appear at relatively low dye concentrations only slightly higher than the second critical micelle concentration. They develop into liquid crystal phase when the dye concentration is further increased. It takes some hours for the formation of a stripe-like texture characteristic of nematic liquid crystals, depending on the methanol content and dye concentration. The combination of the surface active-part and the azobenzene moiety would be responsible for the formation of the liquid crystal.     

Morphology of a Main Chain Liquid Crystal Polymer Containing Semi-Flexible Coupling Chain

A new procedure for the study of textures or director patterns in liquid crystal polymers is reported. The director patterns of the liquid crystal phase are decorated using a lower temperature crystalline phase, a process which does not disrupt the larger scale molecular organisation representative of the liquid crystal structure. The pattern of the decorating crystal lamellae is revealed using an etching technique; the director pattern lies orthogonal to these “lamellae”. Examples are shown of the texture relating to point and line defects. The potential of a quantitative approach to the director distribution about an inversion wall to provide numerical values of the curvature elastic constants is detailed.     

Influence of MWCNT on the properties of hydrogen bonded liquid crystals

A hydrogen bonded complex molded between p-n-octylbenzoicacid (8BA) and m-fluorobenzoic acid (FBA) is isolated and doped with predetermined quantity of Multi Walled Carbon Nano Tube (MWCNT) in order to achieve better thermal and electrical performance. The obtained series of liquid crystal nano systems comprising of three mesogens, varying in the weight percentage of MWCNT are analyzed by Polarizing Optical Microscope (POM), Differential Scanning Calorimetry (DSC) and Fourier Transform Infra-Red (FTIR) spectroscopy. Different aspects of the MWCNT – liquid crystal combination, evaluation of MWCNT's effect on selected properties of liquid crystals which are relevant to display related applications are discussed. In addition, Frederik's transitions of MWCNT dispersed liquid crystals reveal the direct effect of bundles of MWCNT on liquid crystal reorientation.     

Optimization of control parameters of cadmium zinc telluride Bridgman single crystal growth

The temperature gradient within a furnace chamber and the crucible pull rate are the key control parameters for cadmium zinc telluride Bridgman single crystal growth. Their effects on the heat and mass transfer in front of the solid‐liquid interface and the solute segregation in the grown crystal were investigated with numerical modeling. With an increase of the temperature gradient, the convection intensity in the melt in front of the solid‐liquid interface increases almost proportionally to the temperature gradient. The interface concavity decreases rapidly at faster crucible pull rates, while it increases at slow pull rates. Moreover, the solute concentration gradient in the melt in front of the solid‐liquid interface decreases significantly, as does the radial solute segregation in the grown crystal. In general, a decrease of the pull rate leads to a strong decrease of the concavity of the solid‐liquid interface and of the radial solute segregation in the grown crystal, while the axial solute segregation in the grown crystal increases slightly. A combination of a low crucible pull rate with a medium temperature gradient within the furnace chamber will make the radial solute segregation of the grown crystal vanish. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Blue phase liquid crystals stabilized by graphene oxide modified with aminoalkyl group

In the present work, the graphene oxide/blue phase liquid crystal composites and long aminoalkyl chains functionalized graphene/blue phase liquid crystal composites were prepared by doping the additives into a blue phase exhibiting liquid crystal host. It is found that the blue phase temperature range could be widened by dispersing a small amount of functionalized graphene. It suggests that anisotropic two-dimensional flake nanoparticles may be of great usefulness for stabilizing blue phases.     

Captured Orientational Order in Polymer Network Assemblies

Abstract

The “marriage” between low molecular weight liquid crystals and polymers burgeoned in the 1980s with the idea of dispersing liquid crystal droplets in a rigid polymer matrix to create an electrically controllable light scattering medium. The orientation of the liquid crystal droplets, and hence the refractive index match and scattering, can be systematically controlled with an electric field. Today, dispersions of liquid crystals and polymers are found in many forms depending on the concentration of polymer, which can be as large as 70% or as small as 1%. The systems most understood are those of larger concentration where the liquid crystal is segregated out in the form of droplets randomly distributed throughout the surrounding polymer (see page 2). Dispersions of liquid crystals and polymers differ from macroscopic bulk liquid crystals because of the large surface-to-volume ratio and symmetry breaking non-planar geometry imposed by the polymer. Their composite nature profoundly affects the ordering of the liquid crystal, and their susceptibility to external fields makes them suitable for many new electro-optic applications, as well as intellectually challenging to study from the basic science perspective.     

Measurement of the Refractive Index and Estimate of the Order Parameter in Oriented Liquid Crystals

The refractive indices of a cholesteric liquid crystal, cholesteryl dodecyl carbonate (CDC), and a smectic liquid crystal, p-n-octoxybenzilidene-p-n-butylaniline (OOBBA), have been measured as a function of temperature in the transition temperature regions. The measurements were made on oriented liquid crystals with an Abbe refractometer. By combining the data on ordinary and extraordinary refractive indices, the relative order parameter, α_aS/α, is plotted as a function of temperature. The behavior of the order parameter near the cholesteric to isotropic transition of CDC is similar to a nematic liquid crystal, whereas, the order parameter in OOBBA shows only a slight temperature variation like many solids.     

Liquid Crystal Display Research in Japan

The technology development of liquid crystal display started having a remarkable influence on the technology innovation of up-to-date electronic calculator. While a digital display using liquid crystal display has been developed in its earlier stage as the segment type which sets a limit of display to numeric and certain symbols, it is also spent an effort to develop the X - Y matrix type which can display alpha-numeric and moreover kana characters. As a practical application of the X - Y matrix type liquid crystal display, an alpha-numeric type scientific electronic calculator and electronic translator will be reported.

Further, the present status of liquid crystal display applications and trend of R&D in other consumer and industrial electronic industries in Japan will be reported. Finally, activities in the Japanese academic circles will be presented.     

Liquid Crystal Polymers: Conformation of Deuterated Parts by SANS

Comb like liquid crystal polymers are polymers on each monomer is grafted a hanging liquid crystal molecule. The bulk state has the classical liquid crystal phases (nematic, smectic); what is the conformation of a chain in these phases is the problem to solve with the help of small angle neutron scattering. The values of the global sizes R _|| and R _‖ of a chain (in the direction parallel and perpendicular to the director) are discussed as a function of the chemical species and the temperature. Strange results are discussed in terms of segregation of labelled parts.     

Accurate Modelling of Liquid Crystal-Based Microwave Devices

Liquid crystal substrates have been shown to provide the means to develop low-cost, reconfigurable, adaptive and tuneable microwave devices for mobile and wireless communication systems. In order to take maximum advantage of the possibilities that these materials offer and to design LC-based devices appropriately, techniques for the characterisation of the liquid crystal dielectric properties are needed. Similarly, appropriate modelling methods are required to simulate accurately the switching behaviour of the liquid crystal and the characteristics of the wave propagation through the devices, taking full consideration of the point-by-point variation of the material tensor permittivity.     

Synthesis and mesomorphic behavior of symmetrical chiral liquid crystal dimers incorporating ester linked biphenyl- naphthyl cores and terminal vinyl group

A series of symmetrical chiral, liquid crystal dimeric molecules possessing ester- linked, biphenyl-naphthyl cores with varied spacer lengths and terminal vinyl groups have been synthesized using Naproxen as the synthetic precursor. The synthesized symmetrical chiral dimers were characterized by 1H NMR spectroscopy, and their liquid crystalline behavior was confirmed by DSC and HOPM studies. Structural effects on the mesomorphic and physicochemical properties were investigated in terms of variation of chiral chain length. The synthesized dimeric compounds exhibited SmX^*, SmC^*, SmA^*, N^*, BPI^*, and BPII^* mesophase sequences. An odd-even effect was observed in the dimers and the duration of the mesophase decreased with increasing spacer length. The synthesized vinyl substituted liquid crystalline dimers are particularly useful in understanding liquid crystal polymorphism and act as model compounds for liquid crystal polymers.