Phase separation of the liquid crystal in the cholesterin phase

In the ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid [AA]/4-cyano-4'-n-heptyl biphenyl (TCB) solutions, 7CB acted as a diluting reagent when it was added into the (E-CE)C/AA cholesteric liquid crystalline solutions. The dispersed phase with 250–300nm in size appeared after the AA in the isotropic (E-CE)C/AA/7CB solutions with the 7CB concentration (C_7CB) between 27.4 – 41.2wt% was polymerized at 24°C. There was the dispersed phase rich with 7CB in the (E-CE)C/AA/7CB cholesteric liquid crystalline solutions when C_7CB was 43.0wt% at 24°C. The temperature at which the anisotropic phase in the dispersed phase transformed to the isotropic phase in the solutions was increased after the polymerization of the AA, but the transition temperature of the dispersed phase in both the solutions and the films was lower than that of the pure 7CB. Received: 6 October 2000/Revised version: 18 December 2000/Accepted: 28 December 2000     

Synthesis and characterization of cholesteric thermotropic liquid crystalline polyesters

Cholesteric liquid crystalline polyesters were successfully synthesized from isosorbide, methyl hydroquinone, and isophthaloyl chloride. Homo/copolyesters were synthesized by the solution polycondensation method, for which a mild organic base such as pyridine was employed. Inherent viscosities of polyesters P‐3–P‐5 were in the range of 0.31–0.39 dL/g at 25°C in chloroform, and polyesters P‐1 and P‐2 were insoluble in chloroform. Homo/copolyesters based on isosorbide, methyl hydroquinone, and isophthalic acid had thermal stability at more than 300°C on the basis of 10% weight loss. The thermotropic liquid crystalline properties were examined by differential scanning calorimetry and polarizing optical microscopy. Wide‐angle X‐ray diffraction study demonstrated that polyesters P‐1, P‐2, and P‐3 were semicrystalline, whereas the degree of crystallinity of polyesters P‐4 and P‐5 was less than 5%. Copolyester P‐4 showed formation of a yellow iridescent streak at 209°C on heating and development of a Grandjean texture at 270°C on heating. These are typical textures of the cholesteric liquid crystalline phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1232–1237, 2007     

Encoding Hidden Information onto Surfaces Using Polymerized Cholesteric Spherical Reflectors

The omnidirectional Bragg reflection of cholesteric liquid crystals molded into spheres turns them into narrow-band retroreflectors with distinct circular polarization. It is shown that these cholesteric spherical reflectors (CSRs) can encode information onto surfaces for far-field optical read-out without false positives, as the selective retroreflectivity allows the background to be easily subtracted. In order to hide the encoding from detection by the human eye, the retroreflection band is tuned to the near-UV or IR spectra, allowing ubiquitous deployment of CSRs in human-populated environments. This opens diverse application opportunities, for instance, in supporting safe robotic navigation and in augmented reality. A key breakthrough is our ability to permanently embed CSRs in a binder such that undesired scattering and reflections are minimized. This is achieved by realizing CSRs as shells that are polymerized from the liquid crystalline state. The resulting shrinkage around an incompressible fluid deforms the thinnest region of each shell such that it ruptures at a well-defined point. This leaves a single small hole in every CSR that gives access to the interior, allowing complete embedding in the binder with optimized refractive index, minimizing visibility.     

基于Berreman 4×4矩阵对胆甾相液晶Bragg反射带宽的模拟研究

利用Berreman 4×4矩阵和Matlab编程模拟了胆甾相液晶的反射光谱,分析了螺旋数(液晶厚度)、基板的折射率、双折射、折射率色散、固定螺距、梯度螺距和入射角等因素对反射光谱带宽的影响。结果表明,要得到理想的Bragg反射带宽,液晶层的厚度即螺旋数N需达到N≥10;基板折射率会影响最大反射率,基板折射率ng与寻常光折射率no相比,ngno时,最大反射率比较低,ng越小越影响明显,当ng≥no时,具有很好的反射率;折射率的色散和大的入射角会使带宽变窄,而大的双折射Δn和螺距P可以得到较宽的反射带宽,但拓宽效果有限。通过梯度螺距的函数表达式,理论模拟了具有螺距梯度的胆甾相液晶的反射带宽,其对于胆甾相液晶宽波反射的实验研究具有一定的意义。     

平板显示中的双稳态技术：现状与进展（三）

介绍双稳态显示器件的原理、开展双稳态显示技术的意义和基本思路。在此基础上简要介绍现有比较成熟的几种双稳态显示器件的基本原理、基本特性、研究进展和存在的问题。包括以液晶材料为核心的双稳态器件、基于光干涉与机械双稳态机构的iMod显示器件、基于电泳现象的零电场双稳态E-ink显示器件。由于双稳态发展历史已经很长,本篇综述的宗旨不在于介绍最新的发展状况,而在于为提供双稳态显示器件较为完整的创造思想和方法。在液晶显示单元双稳态化的基础上．作者提出OLED阵列、FED阵列的双稳态结构的原理与技术途径。提出通过现有技术的组合,实现显示器件双稳态化的大屏幕显示器件的发展思路。     

低功耗大尺寸胆甾型液晶显示器的发展

与主动发光型显示器相比,反射型显示器具有功耗低,特别是适用于低能耗系统的优势。但在某些情况下,系统的功耗往往大于显示器功耗。     

A Printable Optical Time‐Temperature Integrator Based on Shape Memory in a Chiral Nematic Polymer Network

An optical and irreversible temperature sensor (e.g., a time‐temperature integrator) is reported based on a mechanically embossed chiral‐nematic polymer network. The polymer consists of a chemical and a physical (hydrogen‐bonded) network and has a reflection band in the visible wavelength range. The sensors are produced by mechanical embossing at elevated temperatures. A relative large compressive deformation (up to 10%) is obtained inducing a shift to shorter wavelength of the reflection band (>30 nm). After embossing, a temperature sensor is obtained that exhibits an irreversible optical response. A permanent color shift to longer wavelengths (red) is observed upon heating of the polymer material to temperatures above the glass transition temperature. It is illustrated that the observed permanent color shift is related to shape memory in the polymer material. The films can be printed on a foil, thus showing that these sensors are potentially interesting as time‐temperature integrators for applications in food and pharmaceutical products.     

负性胆甾相液晶电场感应的各平面织构阈值电压及螺距的测定

本文对负性胆甾相液晶在电场作用下织构交替变化现象作了进一步的实验观测。给出了各感应平面阈值电压与外场频率的关系曲线及阈值电压与各感应平面织构螺距数的关系。     

Evaluation of chiral dopants for LCD applications

Abstract— A large number of new synthesized as well as known chiral dopants with respect to their helical twisting power (HTP), the phase stability of cholesteric solution prepared by doping nematic LC mixtures, the host dependence of the chiral induction, and the photostability has been examined. The evaluation led to the result that only few compounds fulfill the stringent application requirements of LCD manufacturing, especially with reference to bistable cholesteric devices.