利用共平面電極結構量測向列型液晶的扭曲彈性係數

Abstract

本實驗證實了一個可用來量測液晶扭曲彈性係數的方法，液晶的扭曲彈性係數(twist elastic constant K22)在許多基礎的研究與應用上，扮演了很重要的角色，例如在表面定向強度的測量。本實驗主要是利用外加高電場來控制液晶光軸(director)的指向，來測量出IPS (In-Plane-Switching)的水平配向液晶樣品，在外加高電場下的臨界電壓值Vth(threshold voltage)，把臨界電壓值Vth代入描述液晶在外加平面電場下的運動行為公式，進而求出扭曲彈性係數K22的值，我們並對此液晶樣品本身作溫度控制，求出液晶在液晶態的溫度範圍中，不同溫度下的K22值。本實驗同時量測了5CB和E7兩種不同的液晶，並與文獻值作比較。

A method of measuring the twist elastic constant (K22) of a nematic liquid crystal (NLC) has been demonstrated. This constant is an important parameter of NLC for both fundamental research and applications. It is also often required to experimentally deduce other parameters of NLC, such as azimuthal anchoring strength. A simple method without applying magnetic field is on demanding. We measured the K22 with a homogeneous cell with laser beam (632.8 nm). An in-plane-switching configuration was used to apply the electric field. The constant can then be obtained by measuring the threshold voltage. The temperature dependence of K22 of 5CB and E7 are measured. The results are compared with other literatures.