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题名	挠曲电效应对液晶器件动态响应速度影响及挠曲电系数测量方法的研究
作者	邢红玉
学位类别	博士
答辩日期	2015-05
授予单位	中国科学院大学
导师	张志东
关键词	挠曲电效应 响应时间 漂移电压 电容 有效介电常数 光导波
其他题名	Research on the Influence of Flexoelectric Effect on the Dynamic Response in Liquid Crystal Display and the Measurement Method to Flexoelectric Coefficient
学位专业	凝聚态物理
中文摘要	挠曲电效应是指液晶形变产生的极化与电场相互作用对液晶分子形变的影响，是一种普遍存在的现象，尤其是具有永久偶极矩的楔形或香蕉形液晶分子发生的展曲或弯曲形变。此效应影响液晶器件的动态响应，其程度决定于液晶的挠曲电系数，导致响应时间随挠曲电系数发生变化。因此，精确确定液晶的挠曲电系数是非常必要的。基于此，本文研究了挠曲电效应对液晶器件动态响应速度的影响及挠曲电系数测量方法的探索，提出了三种测量挠曲电系数的方法。 基于液晶弹性理论和变分原理，研究了弱锚泊混合排列向列相液晶盒中漂移电压与挠曲电系数及锚泊能强度之间的关系，数值模拟得到了其变化曲线。由此可知，通过测量漂移电压可以确定挠曲电系数。 液晶盒本身可以看作是一个电容器。在外加电压作用下，液晶的有效介电常数会发生变化，导致液晶盒电容的改变。基于液晶弹性理论和变分原理，研究了强锚泊平行排列和混合排列液晶盒的电容特性，得到了液晶盒电容解析表达式，并通过数值模拟得到了液晶盒的电容—电压曲线。对于平行盒，挠曲电系数和的绝对值相同、符号不同时c-U曲线相同，并且随挠曲电系数绝对值的增大，挠曲电效应对液晶盒电容的影响越明显。对于混合盒，当e11+e330C/m时，电容随电压线性增加；当e11+e33<0C/m时，电容随电压的增加先减小后增大。因此可以通过对电容的测量来确定挠曲电系数，并给出了具体的实验设计思路。 基于液晶多层光学理论和液晶弹性理论，理论计算得到强锚泊混合排列向列相全漏液晶波导反射率和透射率随内角(光线射入液晶层的角度)的变化曲线。挠曲电系数和取不同的符号(-或+)，全漏液晶波导反射率或透射率变化曲线相对于不考虑挠曲电效应时右移或左移一段距离，并且挠曲电系数数值不同移动的距离也会发生变化。由移动距离可确定挠曲电系数。 基于液晶动力学理论和差分迭代方法，研究了强锚泊混合排列向列相液晶盒撤掉电压时的动态响应过程，通过数值模拟得到了液晶盒透过率随时间的变化曲线。结果表明：随挠曲电系数和的绝对值|e11+e33|的增加，响应时间逐渐减小，当|e11+e33|=50pC/m时，响应时间与忽略挠曲电效应的情况相比缩短了一半的时间。基于自组装的液晶动态响应实验装置，对强锚泊混合排列向列相液晶动态响应过程进行了测量。通过幅度不同的正脉冲电压信号（3V、4V、5V、6V）作用下液晶动态响应实验曲线与考虑挠曲电效应情形下液晶动态响应理论曲线之间的比较，得到了液晶材料E7的挠曲电系数为e11+e33=40pC/m，与文献中报道的实验测量值基本一致。 挠曲电效应会加快液晶动态响应速度的根本原因是在外加电压作用下相对于忽略挠曲电效应情形明显减小了液晶指向矢的形变。因此，当液晶盒撤掉电压时，在弹性形变作用下液晶的动态响应速度自然会加快，为解决液晶显示响应时间长的问题提供了一定的方法。
英文摘要	The flexoelectric effect is the influence on the liquid crystal molecules deformation induced by the interaction between the flexoelectric polarization and electric field, especially the splay or the bend deformation of pear-shaped or banana-shaped liquid crystal molecules with permanent dipole moment. This effect can affect the dynamic response of liquid crystal display (LCD), which is decided by the flexoelectric coefficient of liquid crystal. It results in the variation of response time with flexoelectric coefficient. So, the measurement to the coefficient is very important. Based on this, the influence of flexoelectric effect on dynamic response of LCD and the exploration of measurement method to flexoelectric coefficient were studied in this dissertation, and three methods to determine the flexoelectric coefficient were put forward. Based on the elastic theory of liquid crystal and the variation principle, the relationship between the shift voltage in weak anchoring hybrid aligned nematic cell and flexoelectric coefficient was studied. By computer simulation, the dependence of the shift voltage on the sum of the flexoelectric coefficients and the anchoring energy strength was obtained. As a result, the flexoelectric coefficient can be determined by measuring the shift voltage. Liquid crystal cell itself may be seen as a capacitor. The effective dielectric constant of liquid crystal filled in this cell will change under an external applied voltage, which can result in the variation of the capacitance in liquid crystal cell. Based on liquid crystal elasticity theory and variation principle, the capacitance characteristics of parallel aligned nematic (PAN) and HAN cell were studied, where the analytical expressions of the capacitance for two kinds of cells were also deduced. The capacitance-voltage curves of this cell were simulated numerically. For PAN cell, when the absolute value of the sum of flexoelectric coefficients is the same and not different symbol, the c-U curve is consistent, and the influence of flexoelectric effect on the capacitance of liquid crystal cell is evident with the increasing of the absolute value of flexoelectric coefficient. For HAN cell, with the increase of the applied voltage, the capacitance increases linearly for e11+e330; however, for e11+e33<0, the capacitance begins to decreases and then increases with increasing the applied voltage. Consequently, the flexoelectric coefficient may be determined by measuring the capacitance, and the detailed experimental design was proposed. Based on the multi-layer optical theory and the elastic theory of liquid crystal, the variation curves between the reflectivity and transmittance of the full-leaky liquid crystal waveguide due to the strong anchoring hybrid-aligned nematic liquid crystal and the internal angle (the angle of incidence for which light is incident on the liquid crystal layer) were calculated theoretically. For different sign of the sum of flexoelectric coefficients such as – or +, the variation curves of reflectivity or transmittance of the full-leaky liquid crystal waveguide will move a distance to the left or the right relative to the case of ignoring the flexoelectric effect, and the moved distance will vary with the different flexoelectric coefficients. The flexoelectric coefficients can be known from the moved distance. Based on the dynamic theory of liquid crystal and the finite-difference iterative method, the dynamic response process of strong anchoring hybrid aligned nematic (HAN) liquid crystal cell was studied with removing the applied voltage, and the time-dependent curves of transmittance through the liquid crystal cell were obtained by numerical simulation. The results indicate that the response time will be reduced with the increase of the absolute value of the sum of flexoelectric coefficients |e11+e33| and the response time for |e11+e33|=50pC/m is shortened half time relative to the case with flexoelectric effect ignored. Based on the self-assembly experimental installation, the dynamic response of strong anchoring HAN liquid crystal was measured. Through comparing the experimental curves of the dynamic response of liquid crystal for different positive pulse 3V, 4V, 5V, 6V with the corresponding theoretical curves with the flexoelectric effect considered, the sum of flexoelectric coefficient of liquid crystal material E7 is e11+e33=40pC/m, which is in agreement with the experimental measurement value reported in the literature. The fundamental cause of accelerating the dynamic response speed of liquid crystal induced by flexoelectric effect is that the deformation of liquid crystal director reduces obviously relative to ignoring this effect under the influence of applied voltage. When the external voltage applied into the liquid crystal cell is removed, therefore, the dynamic response of liquid crystal will be speeded up by the action of elastic deformation, which provides the certain method to solve the problem of response time long of liquid crystal display.
公开日期	2015-12-24
内容类型	学位论文
源URL	[http://ir.ciomp.ac.cn/handle/181722/48927]
专题	长春光学精密机械与物理研究所_中科院长春光机所知识产出
推荐引用方式 GB/T 7714	邢红玉. 挠曲电效应对液晶器件动态响应速度影响及挠曲电系数测量方法的研究[D]. 中国科学院大学. 2015.

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