向列型液晶之熱刺激去極化電流

Abstract

熱刺激電流技術是電介質材料在研究微觀介電性質中所使用的基本方法。此技術是先將樣品在高溫以直流電場極化，再將樣品降至低溫，透過線性升溫的方式，使內部結構被系統不同陷阱能階內的空間電荷脫離，或者使取向的偶極分子發生介電鬆弛，此鬆弛能在外部形成位移電流，透過自製的外部電路設計，搭配理論的公式擬和曲線可以獲得材料內部空間電荷與取向偶極分子的活化能和儲存的電荷密度等參數。本論文研究水平排列向列型液晶的熱刺激去極化電流。在接近液晶之澄清點時，會有明顯的峰值電流產生。研究發現熱刺激去極化電流出現的峰值電流將隨著極化電壓的增加而增強。此外，若改變極化的時間，熱刺激去極化電流也將改變。更進一步發現，在升溫速率改變之下，熱刺激去極化電流峰值將會往高溫移動。

Thermally stimulated depolarization current technique is a fundamental method for the investigation of microscopic dielectric characteristics of dielectric materials. In this technique, when a system is applied with a DC voltage source, the energy can be stored in the forms of molecular dipoles, free charges, bonds and reorientation of polar fragments. Normally, as the field being released, the stored energy dissipates, and the system relaxes to its original state. With proper treatment, one can release the energy in the form of electrical current and extract useful information. Based on the measurement of the TSDC, in this study, the mechanism of obtaining phase transition temperatures of liquid crystals is presented. The behavior of the TSDC signal from a typical nematic cell is investigated with pre-applied voltages, polarization time and heating rate as variables.