Nematic polar anchoring strength measured by electric field techniques
Nematic polar anchoring strength measured by electric field techniques
复制标题
DOI：
10.1063/1.371347
复制
发表时间：
1999-10-15
影响因子：
3.2
通讯作者：
Lavrentovich, OD
中科院分区：
文献类型：
--
作者：
Nastishin, YA;Polak, RD;Lavrentovich, OD
我们分析了由Yokoyama和货车Sprang设计的高电场技术[J.Appl.Phys.57，4520（1985）]，以确定液晶-固体基底的极性锚定系数W。该技术意味着同时测量的光学相位延迟和电容的函数的所施加的电压远高于阈值的弗雷德里克转变。我们开发了一个广义的模型，允许W的倾斜导演取向的测定。此外，该模型的结果在一个新的高场技术，（称为RV技术）的基础上的延迟与施加电压的测量。W是从一个简单的线性拟合在一个良好指定的电压窗口。当液晶的介电常数已知时，不需要电容测量来确定W。我们分析的Yokoyama-van Sprang（YvS）和RV技术的有效性，并表明，在真实的细胞的实验数据往往不遵循理论曲线。其原因是指向矢分布在边界板平面内是不均匀的，而理论假设指向矢在该平面内不畸变。这种差异会极大地修改1/W的拟合值，甚至改变其符号，从而使W的确定变得毫无意义。我们建议一个协议，允许一个检查，如果细胞可以用来测量W的YvS或RV技术。该方案确立了原始YvS程序中不存在的新标准。结果进行了比较与其他数据W，通过阈值场技术获得相同的向列基片对。(C)1999年美国物理学会。[S0021-8979（99）07020-6]。
We analyze the high-electric-field technique designed by Yokoyama and van Sprang [J. Appl. Phys. 57, 4520 (1985)] to determine the polar anchoring coefficient W of a nematic liquid crystal-solid substrate. The technique implies simultaneous measurement of the optical phase retardation and capacitance as functions of the applied voltage well above the threshold of the Frederiks transition. We develop a generalized model that allows for the determination of W for tilted director orientation. Furthermore, the model results in a new high-field technique, (referred to as the RV technique), based on the measurement of retardation versus applied voltage. W is determined from a simple linear fit over a well-specified voltage window. No capacitance measurements are needed to determine W when the dielectric constants of the liquid crystal are known. We analyze the validity of the Yokoyama-van Sprang (YvS) and RV techniques and show that experimental data in real cells often do not follow the theoretical curves. The reason is that the director distribution is inhomogeneous in the plane of the bounding plates, while the theory assumes that the director is not distorted in this plane. This discrepancy can greatly modify the fitted value of 1/W, and even change its sign, thus making the determination of W meaningless. We suggest a protocol that allows one to check if the cell can be used to measure W by the YvS or RV techniques. The protocol establishes new criteria that were absent in the original YvS procedure. The results are compared with other data on W, obtained by a threshold-field technique for the same nematic-substrate pair. (C) 1999 American Institute of Physics. [S0021-8979(99)07020-6].