液晶光取向技术

光取向技术是一种非接触式液晶取向方法,它具有无污染、不产生静电、易实现分区取向等优点,因而引起广大科技工作者的关注。本文综述了液晶光取向的最新研究进展,包括液晶光取向研究所选用的材料、各种材料在一定的光照条件下发生的分子结构的变化以及对液晶的取向方式的影响等。     

聚合物分散液晶(PDLC)材料的光聚合反应

以Ar⁺激光器为光源, 采用虎红、N-苯基甘氨酸、二季戊四醇羟基五丙烯酸酯和乙烯基吡咯烷酮分别作为光引发剂、共引发剂、预聚物和稀释剂, 与液晶材料TEB30A结合, 通过光聚合反应, 制备了聚合物分散液晶(PDLC), 用紫外光谱和荧光光谱对其反应机理进行了分析. 实验结果表明, PDLC是通过光引发剂吸收光子能量后与共引发剂相互作用, 形成自由基中间体并引发聚合反应, 使预聚物与液晶产生相分离形成的.     

手性丙烯酸酯液晶原位光聚合反应

手性丙烯酸酯液晶原位光聚合反应何流,张树范,金顺子,漆宗能,王佛松（中国科学院化学研究所北京１０００８０）关键词手性丙烯酸酯,原位光聚合,双折射,近晶相手性侧链液晶高分子显示近晶Ｓ！相,具有铁电性,在光电功能材料和非线性光学材料方面有潜在的应用前景’...     

丙烯酸酯/液晶体系的光聚合反应动力学对PDLC电光性质的影响

采用光-示差扫描量热法（P-DSC） 和光-流变学（P-Rheology）技术,测定了丙烯酸酯/液晶体系的光聚合反应动力学和凝胶化时间. 基于自催化模型和凝胶时间-温度关系,计算了体系的光聚合反应速率常数和活化能,探讨了单体结构与组成、反应温度对体系光聚合动力学的影响,并研究了聚合物分散液晶（PDLC）的电光响应行为与相分离结构对光聚合动力学的依赖性. 结果表明,升高反应温度、增加体系的单体反应活性和平均官能度,均提高了体系的光聚合速率常数,缩短了光聚合凝胶时间. 随着单体反应活性和平均官能度的提高,体系的光聚合反应活化能明显降低,且凝胶化前的光聚合反应活化能低于光聚合全过程的平均反应活化能. 当液晶含量为50%时,形成的PDLC呈亚微米尺度的双连续相结构. 随着光聚合反应温度的升高,光聚合速率加快,导致凝胶时间缩短、相分离程度降低,使PDLC中液晶相尺寸变小、聚合物网络致密化,PDLC的弛豫时间延长、饱和电压降低,而开启时间和阈值电压变化不大.     

锥光干涉法表征偶氮苯侧链液晶聚合物的光致取向

采用偏光显微镜在平行光和锥光条件下对液晶聚合物膜内分子的取向排列状态进行了研究,不同取向状态的膜由线偏振光或圆偏振光照射偶氮苯侧链液晶聚合物得到。结果表明,液晶聚合物膜采用线偏振光照射时,偶氮苯介晶基元沿面排列,形成单相畴面内取向态。该取向态的锥光干涉图为位于视场中心的粗黑十字,旋转载物台小于10°,该干涉图即完全退出...     

新型环氧树脂基液晶光定向层材料的合成与性能研究

经双酚A型环氧树脂与苯胺缩聚反应,制备含有羟基的先驱聚合物EP-AN,通过EP-AN上羟基与肉桂酰氯的酯化反应,制备了侧链带有肉桂酸酯基团的光敏聚合物EP-AN-CI.用核磁共振(1HNMR)、傅里叶红外光谱(FTIR)和热分析等手段确定了上述聚合物的结构与性能.用FTIR等方法表征了EP-AN-CI的光交联反应.经线性偏振光聚合技术(LPP)处理聚合物EP-AN-CI膜制备成液晶定向层,通过装配液晶盒和偏光显微镜观察表明,所制备的定向层具有很好的定向能力,该聚合物是一类具有潜在应用价值的新型液晶光定向层材料.     

新型光取向液晶聚合物的制备及其性能表征

目前,液晶分子常规的定向方法是对涂有定向膜的基片进行摩擦,这种方法简单、方便,然而在摩擦过程中却难以避免产生机械划痕、污染或静电,影响了液晶分子取向的均匀性,光控取向方法是近年来发展起来的一种液晶定向新技术,即通过激光或偏振紫外光照射,引发基片上的聚合物薄膜发生光致聚合、光致异构或光致分解反应,产生表面的各向异性,进而诱导液晶分子取向。     

含氟光敏单体的液晶光控取向研究

制备了系列含氟光敏单体材料, 六氟双酚A双肉桂酸酯(6F-BADE)与含二氟亚甲基结构的肉桂酸酯(FDE-n, n=2, 3, 4). 材料在线性偏振紫外光辐照下均可发生定向光交联反应, 通过红外光谱和凝胶渗透色谱跟踪检测, 表明光交联类型为[2+2]环加成. 单体光聚后形成的取向膜对液晶分子排列效果不同, 6F-BADE取向膜诱导液晶分子垂直排列, FDE-n取向膜诱导液晶分子平行排列. 用原子力显微镜对取向膜表面进行表征, 均未观察到明显的各向异性分布现象. 应用量子力学半经验方法AM1分析发现单体分子极性有较大差异, 认为分子极性的差异是诱导液晶取向不同的主要原因.     

丙烯酸酯/液晶复合体系的光聚合动力学

采用光差示扫描量热分析,研究了以2, 4, 6-三甲基苯甲酰基-二苯基氧化膦(TPO)为光引发剂、丙烯酸异辛酯(EHA)和三羟甲基丙烷三甲基丙烯酸酯(TMPTA)为单体、液晶为P0616A的丙烯酸酯/液晶复合体系在-40~80℃的光聚合动力学。研究表明：丙烯酸酯/液晶复合体系光聚合的自动加速现象非常显著,聚合反应速率和表观动力学常数在聚合过程中均存在最大值。随着反应温度的提高,体系的最终转化率、最大聚合反应速率(Rpmax)均明显提高,当反应温度高于20℃后,其增长均趋于平缓。随着体系中液晶含量的增加,体系的Rpmax呈下降趋势,体系的聚合反应转化率随时间的增长速率较慢,但是最终转化率差别不大,均接近80%。随着UV光强的增高,体系的Rpmax和最终转化率均明显提高, 体系的阈值光强约为4 mw/cm2。而随着体系平均官能度的增加,体系的Rpmax和最终转化率则呈下降的趋势。     

固态光聚合反应研究进展

光引发的固态聚合反应一直是令人感兴趣的研究领域.本文综述了固态光聚合的研究进展.着重介绍了双炔类体系,二烯类体系以及(甲基)丙烯酸酯体系的固态光聚合的研究工作以及应用前景.     

Densely crosslinked liquid single-crystal elastomers

A series of liquid single-crystal elastomers (LSCE) with different crosslinking densities were synthesized. The influence of the crosslinking density on the macroscopic properties (e.g. swelling, thermoelastic behavior and birefringence) and the phase behavior was studied. It is shown that densely crosslinked duromers are available which possess no clearing temperature and exhibit relatively high birefringence at high temperature.     

Recent Results in the Field of Liquid Crystals

Thermotropic mesomorphous phases such as occur in the melts of many organic substances are considered. Though mesomorphous melts were first observed by Reinitzer in 1888, fundamental structural problems regarding such melts have not, as yet, been completely solved. Part I of this article deals mainly with such structural problems and with the theories of crystalline organic liquids. Part II describes the use of nematic solvents for magnetic resonance studies on oriented molecules. Examples are given to illustrate the possibilities offered by this procedure, and some of the results obtained so far are reviewed.     

Chemistry and Applications of Liquid Crystals

Approximately 5% of all organic compounds are transformed at their melting point into liquid crystals—thermodynamically stable, anisotropic liquids which in contrast to isotropic melts appear turbid and are also known as mesophases. Such melts are classed as smectic, nematic, and cholesteric liquid crystalline phases, depending upon the arrangement of the constituent molecules. The discovery of numerous potential applications during the past ten years has awakened the study of liquid crystals from its former slumber as a physical curiosity and placed it in the limelight of the scientific stage. Uses in display systems for measured values and for computer and process data, as well as for remote controlled timetables, for windows of variable light-transmission, etc., appear particularly promising. Not only black-and-white contrasts are now possible but also color production.     

Liquid Crystals: A Tool for Studies on Chirality

Nematic liquid crystals are extremely sensitive to optically active molecules, which, at very low concentration, convert them into cholesteric liquid crystals. The purpose of this report is to review recent applications of liquid crystals to chirality studies. A brief discussion of the structure and properties of liquid crystals is followed by a survey of the methods currently being employed for the determination of the pitch and handedness of cholesteric liquid crystals. Of special interest in the formation of induced-cholestric phases are the twisting powers of optically active compounds and the structural relationships between dopants and nematics. Liquid crystals can be used, inter alia, for the detection of small optical activities and for the determination of thermal racemization barriers and absolute configurations.     

KCD/MDEA/TA三元引发剂引发丙烯酸酯/液晶复合体系光聚合动力学

采用配有441.6 nm滤光片的光差示扫描量热仪研究了3,3′-羰基双(7-二乙胺香豆素)(KCD)/N-甲基二乙醇胺(MDEA)/2-(4-甲氧苯基)-4,6-双(三氯甲基)-1,3,5-三嗪(TA)三元引发剂引发丙烯酸酯/液晶复合体系光聚合动力学行为.结果表明,在KCD/MDEA复合引发剂中添加TA,显著提高了丙烯酸酯/液晶复合体系的最大光聚合速率[Rp(max)]和单体转化率,当TA质量分数为0.5％时,体系的Rp(max)和单体转化率分别提高了100％和69％.同时,随着光照强度的增加,该体系的Rp(max)和单体转化率呈增大的趋势,当光强从1.5 mW/cm2提高到35.2 mW/cm2时,其Rp(max)和最终单体转化率分别提高了2.5和2.8倍.     

Thermal properties and ionic conductivity of a polymer prepared by the in situ photopolymerization of a vinylimidazole monomer containing a mesogenic group

We have synthesized liquid crystalline polymers containing an imidazolium salt moiety and a mesogenic group by the in situ photopolymerization of a liquid crystalline vinylimidazole monomer in order to investigate the relationship between their thermal properties and ionic conductivity. A smectic phase was shown by the vinylimidazole monomer. The in situ photopolymerization of the monomer was carried out in the temperature range of the smectic phase. The polymer thus prepared displayed a highly ordered smectic phase in the temperature range between room temperature and about 200°C. The ionic conductivity of the polymer increased with increasing temperature. Anisotropic ionic conductivity behavior was observed for the polymer. The ionic conductivity of the polymer aligned homogeneously is larger than when homeotropically aligned.     

Cross-Polarisation Applied to the Study of Liquid Crsytalline Ordering

Summary.  Cross polarisation is extensively used in solid state NMR for enhancing signals of nuclei with low gyromagnetic ratio. However, the use of the method for providing quantitative structural and dynamics information is limited. This arises due to the fact that the mechanism which is responsible for cross polarisation namely, the dipolar interaction, has a long range and is also anisotropic. In nematic liquid crystals these limitations are easily overcome since molecules orient in a magnetic field. The uniaxial ordering of the molecules essentially removes problems associated with the angular dependence of the interactions encountered in powdered solids. The molecular motion averages out intermolecular dipolar interaction, while retaining partially averaged intramolecular interaction. In this article the use of cross polarisation for obtaining heteronuclear dipolar couplings and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment were considered and their utility illustrated. A method for obtaining proton–proton dipolar couplings, by utilizing cross polarisation from the dipolar reservoir, is also presented. Corresponding author. E-mail: kvr@sif.iisc.ernet.in Received May 28, 2002; accepted June 19, 2002     

基于液晶取向变化检测有机胺化合物的方法

采用旋涂法在玻璃基底表面制备4-三乙氧基硅基丁腈有机膜.有机膜表面采用丝绒布进行摩擦和5％乙酸水溶液改性处理后成为特异敏感膜.将此敏感膜的载玻片面对面贴合后,在其间组装液晶E7分子膜,表征液晶分子排列状态;采用挥发法在敏感膜表面组装液晶膜,制备成了检测目标物的复合材料.采用此种材料对甲胺、乙胺和二乙胺等有机胺化合物及实验室常见干扰气体进行检测,发现只有有机胺化合物会对材料的液晶分子排列状态产生影响,导致液晶膜的亮度发生改变,从而实现对目标物的特异检测.对有机胺化合物检测过程中,其响应速率为V甲胺＜V乙胺＜V二乙胺,恢复速率为:V乙胺＜V乙胺＜V甲胺;刘乙胺的检出限为0.46 mg/m3.本方法具有较高的检测灵敏度,抗干扰能力较强且操作简单,可发展为现场检测有机胺化合物的新技术.     

Model studies towards liquid crystalline dendrimers with mesogenic repeat units throughout the structure

Model studies towards liquid crystal dendrimers in which the mesogenic units are based on alkoxyalkylbiphenyls and repeat through the structure are described; the parent monomers show smectic mesophases demonstrating the suitability of the motifs.