Full Permanent Memory Effect in PDLC Films

Permanent memory effect in polymer dispersed liquid crystal (PDLC) films prepared by thermal polymerization induced phase separation (PIPS) were studied. New trimethylolpropane trimethacrylate (TMP3MA)/poly(propylene glycol) methacrylate (PPGMA375)/E7/AIBN and pentaerythritol tetraacrylate (PE4A)/poly(propylene glycol) acrylate (PPGA475)/E7/AIBN PDLC films showed 86% permanent memory effect with E90 = 6 V/μm and memory state contrast of 70% and full permanent memory effect with E90 = 3 V/μm and total memory state contrast, respectively. These materials with two stable states (opaque and transparent) seem to be promising for the development of a new class of optical memories as they can be used for electrically write information, optically read the written information and they can be thermally erased back to the initial scattered state.     

连续变焦的聚合物分散液晶电控透镜

介绍了一种基于聚合物分散液晶材料的连续调焦电控透镜.在聚合物分散液晶盒的上表面电极上刻蚀圆孔,形成一个非对称电极,在液晶盒上下极板之间,诱发一个非均匀电场,从而引起聚合物分散液晶材料的折射率非均匀分布,形成电控变焦透镜.阐述了聚合物分散液晶可调焦透镜的基本原理,分析了透镜孔径对聚合物分散液晶透镜焦距的影响,在直径3mm和6mm的圆孔条件下,分别测量了透镜焦距随电压的变化关系.结果表明:电压从50V加到170V的过程中,透镜焦距逐渐减短,刻蚀3mm圆孔的聚合物分散液晶盒焦距从1.361 63m到0.429 21m,刻蚀6mm圆孔的聚合物分散液晶盒焦距从1.769 92m到0.548 43m.     

Effect of macro-RAFT agent on the morphology of polymer dispersed liquid crystals

In this study, macro-(RAFT) reversible additional fragmental chain transfer agent prepared by reversible additional fragmental chain transfer polymerisation has been incorporated into polymer dispersed liquid crystals (PDLCs). The effects of concentration, molecular weight and glass transition temperature of macro-RAFT agent were studied in terms of morphology, polymerisation kinetics, molecular weight of polymer matrix and electro-optical properties of the films. It was found that the key factor influencing morphology was the mobility of macro-RAFT agent chain rather than polymerisation rate and molecular weight of polymer matrix. Furthermore, the decrease in the mobility of macro-RAFT agent chain caused less liquid crystal nematic fraction, smaller liquid crystal domain size and greater driving voltage.     

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     

聚合物网络稳定液晶膜的制备与研究

实验发现在液晶中添加少量的预聚物单体,利用光聚合诱导相分离的方法可以形成反型显示模式的聚合物网络稳定液晶膜。该膜在平时呈现透明态,在电场的调节下呈散射态。本文观察了在不同光照时间、不同光强下制得样品的聚合物网络织构,分析了在聚合过程中形成网络的形状、大小与致密程度,并对实验结果进行了相关的讨论。     

Morphology and electro-optic responses of poly(methyl methacrylate)/nematic liquid crystal composite films: Effect of the polymer molecular weight

The director configuration, state of liquid crystal (LC) phase aggregation, and the electooptic properties of thin polymer films of poly(methyl methacrylate) (PMMA) containing nematic liquid crystal have been studied. Measurements included scanning electron micrograph (SEM), polarized optical micrographs (POM), and transmittance response of the film with the applied electric AC voltage and frequency. Two types of PMMA with significantly different molecular weight (M_w) were used, and the effects of polymer molecular weight on morphology and electro-optic properties of the composite films were examined. © 1995 John Wiley & Sons, Inc.     

液晶／高分子复合显示材料研究进展

综述了近年来液晶／高分子复合电光显示材料的研究进展。概括了液晶高分子复合膜显示材料的最新研究成果，就材料的制备方法、性能和应用前景等方面进行了探讨。     

The effect of molecular weight of polymer matrix on properties of polymer-dispersed liquid crystals

The electro-optical properties and memory effects are important characters of polymer-dispersed liquid crystal (PDLC) devices. Molecular weight of polymer matrix influences the morphology of liquid crystal droplets in PDLC film and the performance of PDLC devices. In this letter, PDLC films were doped with a small amount of chain transfer agent (CTA), in order to control the molecular weight of polymer matrix. It is observed that the addition of CTA induces a reduction of threshold voltage. In addition, the effect of molecular weight on memory effects of PDLC devices was also discussed. It is found that the entanglement between polymer and liquid crystal molecule increased with the molecular weight, which reduces the memory effect.     

An investigation on a novel PDLC film’s fabrication and its electro-optical properties

A polymer dispersed liquid crystal (PDLC) film that has good electro-optical properties is produced by the method of polymerized-induced phase separation. Based on the application foreground, its capability parameters, such as contrast ratio, work voltage, and visual angle, are characterized for the first time by a white light but not a fixed wavelength light. The results show the PDLC film has a low work-voltage of 20 V, more than 150° visual angle, high stability, and long lifetime. The differences between plastic and glass ITO-coated substrates of PDLC films are also studied in this paper. The plastic substrate has better property and will have a wider perspective especially in the portable, tender and folded display devices. Due to adjustable properties of film by electric field, PDLC has the potential application for display device, sensor, switch, grating, and new generation analytical apparatus.     

Optical and morphological characterization of polyacrylamide hydrogel and liquid crystal systems

In this work, the thermotropic liquid crystal MBBA (N-(4-methoxybenzilidene)-4-butylaniline), entrapped on hydrogels, based on cross-linked polyacrylamide (PAAm), was studied. The liquid crystalline phases of system were characterized by polarized optical microscopy (POM), refractive index, optical transmittance, scanning electron microscopy (SEM) and water loss. It was verified the presence of birefringence on hydrogel + liquid crystal. The dynamic of formation of such birefringence finished 40 days after the hydrogel synthesis. The effective birefringence Δn, i.e., the difference on refractive index of polyacrylamide hydrogel to refractive index of hydrogel + liquid crystal (Δn₁) and the difference on refractive index of liquid crystal (MBBA) to refractive index of hydrogel + liquid crystal (Δn₂) are dependent of content of acrylamide (AAm) and MBBA on hydrogel. The increase on Δn₁ and Δn₂ with the polyacrylamide content on hydrogel was attributed to decreasing of the mobility liquid crystal inside the hydrogel. Also, an increase on MBBA concentration in the polymeric matrix provides a reduction in the values of optical transmittance in the system. The morphology observed by SEM shows that hydrogel + liquid crystal is more compact that PAAm hydrogels. The presence of MBBA causes an increase in hydrophobicity. The water loss speed is favored by the increase in the amount of MBBA present in the hydrogels.