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A spin wave theory is proposed to study nematic liquid crystals. Since the orientation of the molecularlong axis and the angular momentum of the molecule rotating around its long axis have the same direction, operatorscan be introduced to research the nematic liquid crystal. By transforming the intermolecular interaction potential,the Hamiltonian of the system has the same form as that of the ferromagnetic substance. The relation of the orderparameters to the reduced temperature can be obtained. It is in good agreement with the experimental results in thelow temperature region. In the high temperature region close to the transition point, by using the Hamiltonian, thetransition point can be obtained, which is near to the Maier-Saupe‘s result. 相似文献
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双轴向列相液晶的Monte Carlo模拟 总被引:1,自引:0,他引:1
利用Monte Carlo方法模拟棒状液晶分子随温度变化的相变行为,采用热力学统计方法得到能量与温度的关系,得出比热随温度的变化规律,通过图像的峰值确定相变点;重点模拟计算序参数矩阵元与温度的关系,得到不同分子结构参数下液晶系统的温度相图,模拟结果显示,当两个短棒长度相等时,不存在双轴相. 相似文献
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We study the propagation of spatial solitons in nematic liquid crystals, using the self-similar method. Analytical solutions in the form of self-similar solitons are obtained exactly. We confirm the stability of these solutions by direct numerical simulation, and find that the stable spatial solitons can exist in various forms, such as Oaussian solitons, radially symmetric solitons, multipole solitons, and soliton vortices. 相似文献
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ZHANGJun TAORui-Bao 《理论物理通讯》2002,37(2):253-256
Phase transition between nematic and isotropic liquid crystal is a very weak first order phase transition.We avoid to use the normal Landau-de Gennes‘s free energy that reduces a strong first order transition,and set up a data base of free energy calculated by means of Tao-Sheng-Lin‘s extended molecular field theory that can explain the experiments of the equilibrium properties of nematic liquid crystal very well.Then we use the free energy method of lattice Boltzmann developed by Oxford group to study the phase decomposition,pattern formation in the flow of the liquid crystal near transition temperature. 相似文献
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Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems 下载免费PDF全文
We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein--Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of
the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals. 相似文献
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向列相液晶(NLC)的取向变化对外界环境敏感,已被作为生物传感的敏感中介材料。研究了侧边抛磨光纤(SPF)用于NLC取向变化测量的传感特性,探索利用SPF测量液晶取向变化的可行性与适用范围。将液晶折射率的理论公式与SPF传输光功率实验数据结合,得到了经验理论关系。实验中设计用机械旋转法改变SPF抛磨面附近NLC的取向。实验结果表明,NLC的取向变化导致SPF传输光功率的变化。以液晶指向矢方位角为表征的NLC的取向变化从0°增大至90°,SPF传输光功率随之增大28.10dB;在0°~30°范围内,SPF传输光功率与NLC的取向变化具有线性关系,光纤传输光功率对取向角度变化的响应平均约为0.359dB/(°)。研究表明SPF可以用于NLC的取向变化的测量并且获得了适用范围,这为基于液晶取向变化的SPF生物传感器的研究提供了参考。 相似文献
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使用修正的Gruhn-Hess空间各向异性两体势模型研究弯曲形变向列相液晶盒.为了易与弹性理论的结果进行比较,做单一弹性常数近似.在理想有序条件下,对模型进行连续化处理,截断到形变的二阶项,给出的自由能密度公式与含k13项的弹性理论公式一致.使用模型直接研究强锚泊弯曲形变向列相盒,没有出现弹性理论给出的边界处不连续.通过Monte Carlo模拟研究发现,两体势中的k13项将加剧弯曲盒中间层的涨落. 相似文献
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研究了一种新型偶氮材料sy03在光控取向中的应用。将sy03加入聚酰亚胺SE-3310(Nissan)与N,N-二甲基甲酰胺(DMF)的混合溶液中作为90°扭曲向列相液晶显示(Twisted nematic liquid crystal display,TN-LCD)的光取向材料,测量由它作为取向膜的扭曲向列型盒的电光特性与仅用SE-3310取向的扭曲向列型盒电光特性比较,发现sy03偶氮的加入使得扭曲向列型盒的响应时间短到98 ms、阈值电压也降低到1.7 V左右。而且随曝光时间的增加,响应时间和衬比度都有所提高,电光响应曲线也更为陡峭。加热到150℃后,其电光特性并没有明显变化,证明了它良好的热稳定性。最后通过测量偏振紫外吸收光谱,分析得出液晶分子易取向方向与激发光源偏振方向垂直。 相似文献
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Hiroyuki Ichikawa 《Optical Review》1997,4(3):395-401
A single-path transmission type twisted nematic liquid crystal panel appears to achieve nearly phase-only spatial light modulation when placed between a properly aligned polarizer and analyzer. We obtained more than π phase delay with the equipment whose retardation was less than π. 相似文献
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电场作用下染料掺杂手性向列相液晶器件激光辐射谱研究 总被引:1,自引:0,他引:1
研究了电场作用下染料掺杂手性向列相液晶器件激光辐射谱。设计了两种电极结构,分别对正性和负性液晶器件施加横向和纵向电场,采用532 nm的Nd∶YAG脉冲固体激光器泵浦样品。对正性液晶器件施加电场,在 630~660 nm范围获得多波长的激光输出。对负性液晶激光器件施加电场,获得调谐范围为18.5 nm的激光输出。由器件织构和光子禁带的变化,进行了深入的分析。正性液晶器件,在电场力矩与扭曲力矩相互竞争过程中,引起液晶的流动,光子禁带上下浮动,因此不仅在禁带边沿,禁带内也出现激光辐射。而负性液晶器件随着电场强度增大,液晶螺距收缩,禁带蓝移,输出激光波长从681.0 nm蓝移到662.5 nm,出射激光波长为光子禁带边沿处。负性液晶器件在电场作用下的稳定性较好。 相似文献
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本文通过全氢液晶材料的核磁共振氢谱(1H NMR)的哈勒关联研究推测了分子序列取向参数,包括随温度变化的双峰距离及全谱图的半高峰宽.通过哈勒拟合并外推所得到的4'-正戊基-4'-氰基联苯(5CB)和混合液晶E7分子取向参数,与其它方法获得的取值一致. 相似文献
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Spatial light modulators whose phase modulation capability (PMC) exceeds 2π are strongly desirable. A double-pass configuration was evaluated to enhance PMC of twisted nematic liquid crystal panels. Theoretical analysis using Jones calculus is given, and it is proved that phase modulation is exactly doubled when the panel is sandwiched by two polarizers. Experiments to measure the PMC were carried out and results coincide well with the theory.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994. 相似文献
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ZHONG Xiaoxia WU Jiada CHEN Shuchao WU Changzheng LI Fuming 《Chinese Journal of Lasers》1997,6(5):403-408
1.IntroductionOpticalphaseconjugationhasbeeninvestigatedextensivelybecauseofitswideapplicationsinimagingtechnology,phase--conjugationlasers,andopticalassociativememorysystems.Notedfortheirlargeopticalreorientationnonlinearities[IJ,nematicliquidcrystals(NLC)havebecomepromisingopticalmediaforapplicationsinthefieldofnonlinearopticsincludingnonlinearphaseconjugation.In1980,Feketectal.[2)firstrealizedphase--conjugationbydegeneratefour--wavemixing(DFWM)inNLCintheisotropicphase.Sincethen,thefie… 相似文献
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The different approximations that have been used in applying Bethe’s cluster model to the nematic-isotropic phase transition
are examined. It is shown that the introduction of a higher order term in the mean field potential of an outer molecule of
the cluster improves the consistency of the theory considerably. In particular, the importance of satisfying Chang’s relation
is emphasized. Calculations are presented of the long and short range order parameters, heat of transition and specific heat
for different values ofz, the number of nearest neighbours around any given molecule, for both nonpolar and antiparallel near neighbour correlations.
Even the new mean field potential appears to be inadequate forz=3. 相似文献