Electro-optical properties of a PDLC based on unsaturated polyester resin

An electro-optical characterisation of a polymer-dispersed liquid crystal (PDLC) based on unsaturated polyester (UP) resin, recently prepared in our laboratory, is presented. Transmittance and response times as a function of an electric field applied to the sample, have been measured taking into account also the morphological aspects of various samples. The experimental results confirm the theoretical data previously calculated on the base of the dimensions of the liquid-crystal droplets inside the polymeric matrix. Our analysis on this new material suggests the possibility of employing such a PDLC to realise electro-optical devices. Received: 9 October 1998 / Revised version: 12 May 1999 / Published online: 21 January 2000     

A comparative simulation study on three lattice systems for the phase separation of polymer-dispersed liquid crystals

This article reports a comparative study of the phase separation process in a polymer-dispersed liquid crystal, based on a Metropolis Monte Carlo simulation study of three lattice systems. We propose a model for the different processes occurring in the formation of polymer-dispersed liquid crystals (PDLCs). The mechanism of PDLC is studied as a function of quench temperature, concentration and degree of polymerization of liquid crystals and polymers. The obtained resultant phase diagrams of the three systems are approximated and compared with the Flory-Huggins theory, and show a good agreement. It has been observed in the simulation results that among all the three systems, the 40 × 40 × 40 lattice showed the most accurate, reliable and stable results.      

聚合物弥散液晶材料在1550nm的电光特性研究

实验研究了不同配方及工艺条件下,聚合物弥散液晶（PDLC）材料在1550nm处的电控光透射特性。由此筛选合适的配方和工艺,研制了聚合物弥散液晶电控可调光衰减器样品。实验说明,在1550nm工作点,50％左右合适的液晶含量的聚合物弥散液晶样品能够获得更好的电控光学性能。采用配方质量比ω（DHPA）：ω（E7）：ω（RB）：ω（NVP）：ω（NPG）=100：100：3：2：1．5的配方,制作在1550nm工作的聚合物弥散液晶光衰减器样品。经检测,输入光源为1550mm,223μW时,器件插入损耗为2．3dB,衰减调节范围为13dB,线性工作区域为20～70V。     

聚合物分散液晶的制备及拉曼光谱分析

用溶致相分离的方法制备了以PMMA为基体的四种不同配比的聚合物分散液晶(PDLC),四氢呋喃为引发剂,并且通过傅立叶拉曼光谱仪对其进行检测,分析其光谱,观察各单体混合前后性质的变化,鉴别聚合物分散液晶的物质构成。此外,在指定的组分前提下,根据液晶最强峰与PMMA特征峰的相对强度拟合曲线得出PDLC中液晶与PMMA的质量百分比,为下一步研究聚合物分散液晶系统的光折变特性提供指导。     

PDLC-based VOA with a small polarization dependent loss

A polymer-dispersed liquid crystal (PDLC)-based variable optical attenuator (VOA) was demonstrated to exhibit a relatively small polarization dependent loss (PDL) in the optical communication C band. The influence of the PDLC characteristics, the temperature, as well as the wavelength of the laser irradiation, on the PDLC VOA performance was analyzed. The PDL, the insertion loss at saturated voltage, and the operating voltage of the PDLC-based VOA were reduced by optimizing the fabrication conditions and applying a bias voltage to the PDLC cells during polymerization-induced phase separation.     

Study on the algorithm of computational ghost imaging based on discrete fourier transform measurement matrix

We have developed a model and realized an algorithm for the calculation of the coefficient of coherent (direct) transmission of light through a layer of liquid crystal (LC) droplets in a polymer matrix. The model is based on the Hulst anomalous diffraction approximation for describing the scattering by an individual particle and the Foldy-Twersky approximation for a coherent field. It allows one to investigate polymer dispersed LC (PDLC) materials with homogeneous and inhomogeneous interphase surface anchoring on the droplet surface. In order to calculate the configuration of the field of the local director in the droplet, the relaxation method of solving the problem of minimization of the free energy volume density has been used. We have verified the model by comparison with experiment under the inverse regime of the ionic modification of the LC-polymer interphase boundary. The model makes it possible to solve problems of optimization of the optical response of PDLC films in relation to their thickness and optical characteristics of the polymer matrix, sizes, polydispersity, concentration, and anisometry parameters of droplets. Based on this model, we have proposed a technique for estimating the size of LC droplets from the data on the dependence of the transmission coefficient on the applied voltage.     

Laser beam manipulation by composite material electro-optic devices

Liquid crystals are anisotropic materials whose optical properties can be easily controlled applying an electric field. For this reason, they are widely used in electro-optical devices. Besides other applications, liquid crystals electro-optical devices are suitable for laser beam manipulation. In this paper, we present some devices developed or studied in our laboratory: a twisted nematic liquid crystal (TN-LC) polarization rotator, a TN-LC protected light sensor, a polymer dispersed liquid crystal (PDLC) light modulator, a PDLC optoelectronic polarizer and a polymer liquid crystal (PoLiCryst) light modulator.     

柔性PDLC的实验规律

以制作性能良好的柔性PDLC为目标,从材料的选取、制作过程和电光特性等方面进行了研究。电极和聚合物选用柔性的ITO导电膜和紫外固化光学胶NOA65,液晶为向列相液晶混合物P0616A,采用紫外光聚合法,制作出具有柔性的聚合物分散液晶PDLC;测试了不同膜厚和混合比下的PDLC的电光特性和其光谱响应;从而得出了关于柔性聚合物分散液晶PDLC的一些实验规律和结论     

Fast electro-optical switching and high contrast ratio in epoxy-based polymer dispersed liquid crystals

We report the observation of an electro-optical switching effect from an opaque to a transparent state occurring at a threshold value of the applied field in a polymer dispersed liquid crystal (PDLC). Optical responses of the composite film under the conditions of an externally applied ac electric field (2–5 V_p−p/μ) and a film thickness (50 μm), were determined using an Argon laser (wavelength 514 nm). The experimental results showed promising switching times with a rise time of 190 μs and a decay time of 2 ms and an exceptionally high contrast ratio up to 410. These results demonstrate the validity of employing this new PDLC in electro-optical devices.     

纳米银掺杂的高效率全息聚合物分散液晶光栅制备

报道了一种基于掺杂纳米银聚合物分散液晶(PDLC)材料的高衍射率全息电控光栅的制备及特性。通过在原有聚合物分散液晶材料体系中添加适量的纳米银颗粒以制备体全息光栅,实验研究了掺杂不同质量比的纳米银颗粒对全息聚合物分散液晶(H-PDLC)体光栅的衍射效率、驱动阈值电压、响应时间的影响。实验结果表明,通过掺杂纳米银材料,能够优化聚合物和液晶两相分离结构,使聚合物与液晶分离更加彻底,显著提高H-PDLC体光栅的一级衍射效率,同时能改善体光栅的电光特性,缩短响应时间。初步分析表明,由于纳米银颗粒的表面等离子体效应和体系折射率匹配的优化改善了H-PDLC光栅的特性。     

Low threshold and high contrast polymer dispersed liquid crystal grating based on twisted nematic polarization modulator

An electrically tunable mode is proposed to overcome the bottleneck problem of a conventional polymer dispersed liquid crystal (PDLC) grating and realize its low threshold and high contrast through an alignment-controlled PDLC. The results indicate that the threshold voltage V_PP of the grating is as low as 0.75–0.8 V, the saturation voltage V_pp is 7 V and the contrast ratio of the grating reaches 245, which is about three times larger than the conventional PDLC grating. Stability testing indicates a stable state of contrast during a long time. PACS 42.40.Eq; 42.70.Df; 42.79.Kr     

Orientational photorefractive effects observed in polymer-dispersed liquid crystals

We present a novel type of photorefractive polymer-dispersed liquid crystal (PDLC) that contains a polymer, low-molecular liquid crystals (LC's), and a photoconductive sensitizer. Photorefractivity is demonstrated by two-beam-coupling experiments with an external dc field. This material shows highly sensitive photorefractivity, and a purely refractive-index grating (Dn >/= 3.0 x 10(-3)) is generated by irradiation of interference light (lambda=632.8 nm) . The grating in the photorefractive PDLC's shows strong anisotropy, and the dynamics depends strongly on the composition. In the case of a 40:60 weight ratio of polymer:LC's, the photorefractive PDLC's present a stable memory effect.     

应变液晶的负压光效应和反式压光效应

介绍聚合物分散液晶和应变液晶概念,给出聚合物分散液晶调光玻璃的"正压光效应"、"负压光效应"和"反式压光效应"三种效应定义.实验制备出负压光效应和反式压光效应新型应变调光玻璃样品,测试样品散射态雾度90%以上,半透明态透光率接近30%.用偏光显微术研究压光效应原理,表明对样品施加垂面按压或拉伸的应力诱导作用会引起液晶微滴中液晶分子具有某些特殊排列方式,导致样品光学性质发生显著变化.建立垂面拉伸液晶微滴模型,计算模拟所绘出的图形与偏光显微镜照片独特花样十分相似,进而合理解释了实验现象.应变液晶压光效应研究具有聚合物分散液晶基础研究意义和开发非电控调光玻璃的实际应用价值.     

电控聚合物分散液晶变焦全息透镜制作

介绍了相位型全息聚合物分散液晶(PDLC)材料全息透镜,在电场作用下液晶微滴折射率逐渐与聚合物折射率匹配,实现透镜电控变焦。研究了微米尺寸和纳米尺寸液晶微滴聚合物分散液晶材料配方特性和微观结构。采用优化纳米尺寸材料配方制作5~6μm聚合物分散液晶盒,采用离轴式平面波和球面波干涉全息写入光路,成功制作电控变焦聚合物分散液晶全息透镜样品。该透镜样品焦距为20 mm,能够正一级衍射放大成像。实现“0”,“1”变焦的驱动电压阈值为60 V。并进一步提出了基于聚合物分散液晶电控变焦元件集成叠加技术实现电控变焦光学成像系统的技术思路。     

聚合物分散液晶(PDLC)光栅的制备及其光衍射特性

聚合物分散液晶（ＰＤＬＣ）光栅的制备及其光衍射特性任洪文黄锡珉王宗凯马凯（中国科学院长春物理研究所北方液晶研究开发中心长春１３００２１）ＦａｂｒｉｃａｔｉｏｎｏｆＰＤＬＣＧｒａｔｉｎｇａｎｄＩｔｓＯｐｔｉｃａｌＤｉｆｒａｃｔｉｖｅＰｒｏｐｅｒｔｉｅｓ...     

The effect of matrix composition on the electro-optical properties of polymer dispersed liquid crystal

A new type of polymer dispersed liquid crystal (PDLC) composite film has been made by polymerizing the mixture of di-methacrylates, methacrylates containing various groups and E-7. It was found that the long chain alkyl and mesogenic groups in methacrylate monomers greatly affected the saturation and threshold voltages and response time. The sharpness could be improved by addition of methacrylate monomers containing long chain alkyl and 4-butoxylbisphenyl based mesogenic group in appropriate ratios.     

Color dispersion in two-dimensional phase array based on polymer-dispersed liquid crystal film

This work proposes a feasible method for fabricating a two-dimensional periodic structure with a sub-micrometer periodicity using a single laser beam, based on polymer-dispersed liquid crystal (PDLC) films. The resulting nano-PDLC morphology is highly symmetrical, and similar to that written using multi-beam interference. The increase in the electric-tunability of the optical behavior, including spatial diffraction and color dispersion, is examined. The color dispersion provides optical evidence of the periodic structure of the PDLC film.     

用偏光显微术研究聚合物分散液晶压光效应膜

制备出大液晶微滴的具有压光效应的聚合物分散液晶膜,给出样品按压前后偏光显微镜对比照片.提出压缩液晶微滴模型,采用Fortran软件模拟计算了压光效应液晶微滴双折射透光率分布,用Origin软件作图,计算结果绘图与偏光显微镜图片一致.定义按压后液晶微滴圆球变扁球的扁平度,计算按压后序参数与扁平度的关系,说明按压作用使液晶...     

聚合物分散液晶光栅的衍射特性的研究

报道了一种由聚合物分散液晶膜与具有周期性条状电极结构板结合的新型光栅器件，借助于聚合物分散液晶膜的电光特性，这种栅对入射光的散射或衍射取决于对其施加的电压，即它是电场可调的，实验结果显示出当驱动电压超过器件器件阈值电压时，衍射光的强度和衍射斑的可见级次被电场调制，而且它能入射光的线性偏振态变为椭圆偏振态。     

Total internal reflection holographic gratings recorded in polymer-dispersed liquid crystals

We report diffraction gratings recording in polymer dispersed liquid crystals (PDLC) material with a beam suffering total internal reflection from the sample air surface. The real time diffraction efficiency kinetics as well as the polarization, voltage behavior and angular selectivity of the gratings are studied at different reconstruction geometries. An increase of three times of the diffraction efficiency in case of applied voltage is observed for one of these geometries in opposite to typical PDLC switchable gratings. Such dependence appears in most of the geometries and is connected to the specific formation of two gratings by the Stetson scheme.