液晶显示用取向材料聚甲基丙烯酸肉桂酰氧基乙酯的光控取向研究

通过实验研究了光聚合物材料聚甲基丙烯酸肉桂酰氧基乙酯（ＣＥＭＣ）的光化学反应过程, 以及对液晶材料ＬＣ－６７１０Ａ 的取向能力． 通过原子力显微镜（ＡＦＭ）观察了取向层表面在光化学反应前后的变化, 测量了光控取向膜液晶盒中液晶分子的预倾角及单面光控取向扭曲向列液晶显示器（ＴＮＬＣＤ）的电光特性和时间响应特性曲线, 研究了液晶分子排列取向的机理．     

液晶显示用取向材料聚甲基丙烯酸肉柱酰氧基乙酯的光控取向研究

通过实验研究了光聚合物材料聚甲基丙烯酸肉柱酰氧基乙酯（ＣＥＭＣ）的光化学反应过程,以及对液晶材料ＬＣ－６７０１Ａ的取向能力。通过原子力显微镜（ＡＦＭ）观察了取向层表面在光化学反应前后的变化,测量了光控了以向膜液晶盒中液晶分子的预倾角及单面光控取向扭曲现列液晶显示器（ＴＮＬＣＤ）的电光特性和时间响应特性曲线,研究了液晶分子排列取向的机理。     

基于反应力场的分子动力学方法研究氢在钯表面的分解

基于二阶矩近似反应力场方法构建的全维度势能面研究了氢分子及其同位素分子在钯表面的分解过程.在构建势能面的过程中数据库中只包含了氢分子与钯（111）表面相互作用的相关信息,该势能面在研究氢分子在钯（100）表面上的分解过程中表现出了非常好的可转移性.结果表明,氢分子及其同位素分子在钯（111）与钯（100）表面上的分解系数S₀均随着入射能量的增加呈现非单调变化,并且通过固定分子取向的方法发现同核分子（H₂、D₂和T₂）最有利分解取向角为90°,而异核分子（HD、HT和DT）受质心偏移的影响,其最有利分解取向角向大角度偏移.     

向列相液晶$lt;i$gt;n$lt;/i$gt;CB(4-$lt;i$gt;n$lt;/i$gt;-alkyl-4′-cyanobiphenyls, $lt;i$gt;n$lt;/i$gt;=5—8)的旋转黏度及其奇偶效应的分子动力学模拟

在全原子力场模型的基础上,对向列液晶nCB（4-n-alkyl-4′-cyanobiphenyls, n=5—8）进行了等压等温NPT系综下的分子动力学（MD）模拟.对MD的轨迹分析得到了二阶和四阶序参数以及描述液晶分子翻转运动的取向时间相关函数（TCF）,并通过一个近似的单指函数对TCF拟合得到了相关时间.在此基础上,计算了nCB（n=5—8）的旋转扩散系数（Rotational diffusion coefficient, RDC）.利用基于统计力学模型的Nemtsov-Zakharov方法和Fialkowski方法,分别计算了它们的旋转黏度系数（rotational viscosity coefficient, RVC）,进而分别讨论了RVC,RDC和相关时间的奇偶效应.与文献中的实验结果比较表明,该方法得到了合理的计算结果和一致的奇偶效应. 关键词： 旋转黏度 奇偶效应 分子动力学模拟 向列相液晶     

存在光致异构化情况下掺杂液晶非线性增强因子的微观形式

针对偶氮染料掺杂向列型液晶的光学重新取向问题，采用一个与实际光致异构化过程更为接近的染料分子四能级模型，并通过微观分析方法求解四能级速率方程组，得到了与系统分子参数有关的增强因子微观表达式.该表达式说明了偶氮染料掺杂液晶取向光学非线性增强的根源，揭示了在存在光致异构和不存在光致异构两种情况下液晶取向光学非线性增强的内在特点和机理.从四能级模型增强因子出发，通过合并其中某些参数，或使其中某些参数为零，推得了三能级模型下增强因子的形式和入射光波长不处于顺式吸收带内时增强因子的表达式.通过比较分析，说明了用四能级模型解释偶氮染料掺杂向列型液晶非线性增强机理具有优越性.并指出，当入射光波长不处于顺式吸收带时，在快速响应条件下，理论与Marrucci针对蒽醌染料掺杂液晶提出的修正理论具有一致性. 关键词： 四能级模型 偶氮染料掺杂液晶 光学重新取向 光致异构化     

摩擦基板间液晶薄层的分子场理论

提出一种新的表面作用势用于描写摩擦基板对液晶分子的作用.通过分子场理论研究摩擦基板间的液晶薄层,基板作用使液晶分子沿面平行排列.采用Lebwohl Lasher模型,将分子质心固定在简单立方晶格的格点上.对20个分子层构成的液晶薄层进行了数值计算.存在3种分子优先取向方向不同的状态,优先取向方向沿摩擦方向的状态具有最低自由能,并考虑了基板作用引起的双轴对称性.     

光控二维光子晶体光开关

提出了一种调节液晶光子晶体光子带隙的方法。二维三角介质柱形光子晶体位于2块熔凝石英片之间,在介质柱之间填充各向同性排列的液晶,受偏振紫外光照射后,光诱导液晶分子定向排列,通过光诱导液晶分子取向改变液晶的折射率。数值模拟结果表明：通过外界光场控制所填充的向列相液晶分子的方向可以对这种二维三角形介质柱光子晶体的禁带结构进行调节。该可调光子晶体可控制波导中TM模和TE模的选择性传输,因而可应用于制作全光光开关。     

聚甲基丙烯酸肉桂酰氧基乙酯的光化学反应在液晶分子排列取向中的作用

研究了光聚合物材料聚甲基丙烯酸肉桂酰氧基乙酯(CEMC)对液晶材料LC-6710A的取向作用,取向层表面在光化学反应前后的变化;测量了光控取向膜液晶盒中液晶分子的预倾角及单面光控取向扭曲向列液晶显示器(TNLCD)的电光特性和时间响应特性,研究了这种材料的光化学反应过程,以及液晶分子排列取向的机理.     

用喇曼光谱测定液晶的序参数

液晶序参数的测定是研究液晶分子排列的重要课题[1,2].本文介绍我们用喇曼光谱测定MBBA(4-甲氧基苄叉-4’-正丁基苯胺)序参数的结果,与文献比较,基本相符. Jen[2]等人对于液晶序参数作了详尽的论述.令向列型液晶分子长轴与液晶光轴成θ角,那么序参数A0(2)和A0(4)的定义为<>是对所有分子的平均值. 用喇曼光谱测定序参数,主要是测二组退偏比.如图1,激光束垂直入射于经沿面校列处理过的液晶盒.如果a与b分别为散射光和入射光的偏振方向,Iab代表测得的谱带强度.那么退偏比R1和R2[2]的定义是 因此通过退偏比的测量,可以求出序参数的数值. 实验…     

热致液晶CPHOB的有序参数与核磁共振弛豫

从室温至380K测量了热致液晶4-己氧基苯甲酸4-氰基苯酯（CPHOB）的氢核磁共振谱．其固态至向列相的转变温度T_sn=347K，向列相至各向同性液体的转变温度T_ni=359K．得到了液晶态有序参数的温度关系．讨论了氢核磁共振的自旋晶格弛豫机制． 关键词：     

Phase transitions in 8CB liquid crystal confined to a controlled-pore glass: Deuteron NMR and small angle X-ray scattering studies

We present results of the deuteron nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS) study of ordering and phase transition behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG) with nontreated and silanes-treated pore surfaces. The deuteron NMR spectra allowed to determine the degree of nematic liquid crystal ordering and also provided an indirect information on the confined 8CB smectic ordering via its influence on the nematic ordering. For the smectic phase these data are supplemented with measurements of the temperature dependence of the first-order SAXS diffraction pattern. The NMR results indicate that the average nematic and smectic order parameters of 8CB in the nontreated CPG are only weakly perturbed by the confinement. The SAXS data further suggest that in confined 8CB for both nontreated and silane-treated CPG a domainlike pattern appears in accordance with the Imry-Ma theorem.     

Order parameter and its critical exponent for some binary mixtures showing induced nematic phase

Refractive index measurements as a function of temperature have been performed for an induced nematic binary system by means of thin prism technique. The temperature dependence of the birefringence (Δn) has been assessed from the measured refractive index data. A direct extrapolation method has been employed to determine the orientational order parameter for the investigated mixtures and the order parameter so obtained has also been compared with the mean field values. The Haller type fitting expression results in a relatively lower value of the order parameter critical exponent (β) compared to the theoretically predicted values. Therefore, a four-parameter power law expression, consistent with the mean field theory as well as the first-order character of the nematic–isotropic (N-I) phase transition have been used to explore the critical behavior of the order parameter near the N-I transition.     

Study of optical parameters of two fluorinated isothiocyanato nematic liquid crystals exhibiting high birefringence

Optical studies have been carried out on two fluorinated isothiocyanato nematic liquid crystal (LC) compounds 4′-butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4′-pentylcyclohexyl-3, 5-difluoro-4-isothiocynatobiphenyl. Transition temperatures of the two samples were confirmed using a polarizing microscope. The two LC compounds were found to exhibit fairly high clearing temperatures. Measurements of refractive indices of the two compounds were done by using thin prism method with He-Ne laser beam of wavelength 630 nm. Birefringence of the two LC compounds was calculated from the measured refractive indices. Both the compounds are found to display fairly high values of birefringence. Validation of a modified four-parameter model, based on Vuks equation describing the temperature dependence of refractive indices of the two liquid crystals, is also presented in this paper. The model is validated by fitting the experimentally measured values of refractive indices, birefringence and average refractive indices of the two nematic LCs with the theoretical values. In this paper, the calculation of order parameters of the LCs is presented by using two methods: direct extrapolation method based solely on the birefringence data and by using modified Vuks method based on Haller’s extrapolation. As observed from the obtained results, this procedure of calculating order parameter gives very reasonable results.     

H and C NMR studies of molecular orientation and dynamics in liquid crystal 6BA

The dynamics and orientation of dimers accompanying the formation and destruction of hydrogen bonds in the nematic phases of 4-n-hexylbenzoic acid (6BA) were studied by ¹³C and ²H NMR. The orientational order parameter S in the nematic phase was estimated from the quadrupole splitting of the ²H NMR spectrum. The intermolecular interaction energy for the molecular order in the nematic phase decreased with increasing temperature. The flexibility of dimers due to the destruction of the hydrogen bond is closely related to a decrease in the intermolecular interaction energy. The proportion of ²H NMR spin-lattice relaxation time (T₁) to S, which reveals the coupling of the orientational fluctuations with the hydrogen bonding processes, was observed.     

Nematic order and nuclear magnetic relaxation in PCH-3 liquid crystal

Proton NMR was employed to study the nematic phases upon heating and upon cooling in PCH-3 (trans-4 (4-propylcyclohexy) benzonitrile). Our systematic measurements of the nematic order parameter and spin relaxations reveal the microscopic nature of the thermal hysteresis in this relatively low molecular weight nematic liquid crystalline material.     

Biaxial nematic phase in a thermotropic liquid-crystalline side-chain polymer

We report on variable-angle deuterium NMR measurements of nematic liquid-crystalline side-chain polymers, where we have found proof of the existence of a biaxial nematic phase in a system with a side-on attachment of the mesogenic group to the polymer backbone. This provides efficient coupling to the polymer backbone and thus stabilizes the as yet elusive biaxial phase. The experimental approach is validated on a uniaxial end-on nematic polymer, and the reliability of the results is investigated in detail using two-dimensional correlation spectra, providing information on director distribution effects.     

Detecting columnar deformations in a supermesogenic octapode by proton NMR relaxometry

We used proton ( ¹H nuclear magnetic relaxation (NMR) dispersions to study the molecular dynamics in the isotropic phase and mesophases (nematic and columnar hexagonal) of a supermesogenic octapode formed by laterally connecting calamitic mesogens to an inorganic silsesquioxane cube through flexible spacers. The dispersions of the spin-lattice relaxation time (T₁) are interpreted through relaxation mechanisms used for the study of molecular dynamics in low-molar-mass liquid crystals but adapted to the case of liquid crystalline supermolecules. At high frequencies (above 10MHz) the behaviour of the T₁ with the Larmor frequency is similar for all phases and is ascribed to local reorientations and/or rotations. At intermediate and low frequencies (below 10MHz) our results show notable differences in the T₁ behaviour with respect to the mesophases. The nematic (N) and isotropic (Iso) phases’ low-frequency results are similar and are interpreted for both phases in terms of order director fluctuations (ODF), revealing that even in the isotropic phase local nematic order is detected by proton NMR relaxometry. Local nematic order in the Iso phase is interpreted in terms of the presence of nematic cybotactic clusters induced by the interdigitation of mesogens that is promoted by the silsesquioxane octapode molecular structure. In the columnar hexagonal (Col _h phase, the T₁ dispersions show that elastic columnar deformations (ECD) dominate the nuclear magnetic relaxation below 10MHz. This result shows that the columnar packing of the octapode clearly restricts the collective fluctuations of the mesogenic units inspite of their local nematic order.     

Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

ABSTRACT

This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.     

Measurement of dipolar couplings in partially oriented molecules by local field NMR spectroscopy with low-power decoupling

Low-power phase-modulated Lee–Goldburg homonuclear decoupling was used to record PDLF spectra of fluorine-substituted benzene derivatives dissolved in nematic thermotropic liquid crystalline solvents. The low-power decoupling minimizes sample heating during RF irradiation while still achieving highly resolved PDLF spectra. The method is illustrated by recording spectra for 1,3-dichloro-4-fluoro-5-nitrobenzene, 1,3-dichloro-4-fluorobenzene, and 1,2-difluorobenzene dissolved in different nematic solvents.