Yu Tsung-Chih, Lo Yu-Lung, Huang Rei-Rong
Department of Mechanical Engineering, National Cheng Kung University, Tainan, 701, Taiwan.
Opt Express. 2010 Sep 27;18(20):21169-82. doi: 10.1364/OE.18.021169.
Two external-field-free methods are presented for measuring the azimuthal anchoring strength in twisted nematic liquid crystal (TNLC) cells. For asymmetrical TNLC samples, the twist angle is derived from the phase of the detected signal in a phase-sensitive heterodyne polarimeter and is then used to calculate the weak anchoring strength directly. The measurement resolution which is found to be about 0.01 μJ/m(2) makes the present method sensitive enough for the LC-based bio-sensing application. Using the proposed method, the weak azimuthal anchoring strength of a composite liquid crystal mixture (40% LCT-061153 + 60% MJO-42761) in contact with a plasma-alignment layer is found to be 7.19 μJ/m(2). For symmetrical TNLC samples, the liquid crystals are injected into a wedge cell, and the two-dimensional distributions of the twist angle and cell gap are extracted from the detected phase distribution using a genetic algorithm (GA). The azimuthal anchoring strength is then obtained by applying a fitting technique to the twist angle vs. cell gap curve. Utilizing the proposed approach, it is shown that the strong anchoring strength between a rubbed polyimide (PI) alignment layer and E7 liquid crystal is around 160 μJ/m(2) while that between a rubbed PI alignment layer and MLC-7023 liquid crystal is approximately 32 μJ/m(2).
本文提出了两种无外场方法来测量扭曲向列相液晶（TNLC）盒中的方位角锚定强度。对于非对称TNLC样品，通过相敏外差偏振计中检测信号的相位得出扭曲角，然后直接用于计算弱锚定强度。测量分辨率约为0.01 μJ/m²，这使得本方法对基于液晶的生物传感应用足够灵敏。使用所提出的方法，发现与等离子体取向层接触的复合液晶混合物（40% LCT - 061153 + 60% MJO - 42761）的弱方位角锚定强度为7.19 μJ/m²。对于对称TNLC样品，将液晶注入楔形盒中，并使用遗传算法（GA）从检测到的相位分布中提取扭曲角和盒间隙的二维分布。然后通过对扭曲角与盒间隙曲线应用拟合技术来获得方位角锚定强度。利用所提出的方法表明，摩擦聚酰亚胺（PI）取向层与E7液晶之间的强锚定强度约为160 μJ/m²，而摩擦PI取向层与MLC - 7023液晶之间的强锚定强度约为32 μJ/m²。
