液晶分子軸向對液晶聚合物薄膜表面能影響之研究

Abstract

本研究驗證液晶分子軸向在外加電場作用下造成電控液晶聚合物薄膜之表面自由能改變。由歷史文獻中，大部分對於液晶分子形成界面時，其表面自由能的探討皆是未討論液晶分子軸向，J. Cognard在1984年以簡易實驗測出液晶分子垂直及水平排列形成界面時之表面自由能，但並未作深入液晶分子軸向與表面自由能之分析。本論文主要利用液晶聚合物薄膜研究與探討液晶分子軸向於外加電場下與表面自由能之關係。我們先以實驗方式利用邊界條件控制液晶分子的排列，找出單一液晶分子氰基端的表面自由能，再由液晶聚合物薄膜上施加之電場與整體表面自由能的實驗結果，以異物質表面自由能理論(Cassie’s model)推算出液晶聚合物薄膜中液晶部分的表面自由能以及對應傾角。最後我們並利用分析出來的液晶聚合物薄膜之表面自由能，使之對液晶分子配向，並製作一相位調制器並做相關分析。了解施加電壓與液晶分子傾角及表面自由能的關係，可幫助我們設計不同的生物感測器、光電開關、變焦透鏡及其他液晶光電元件。

In this thesis we proved that the surface free energy of the liquid crystal and polymer composite film (LCPCF) is electrically tunable owing to the orientation of liquid crystal (LC) molecules. In the literatures, the effect of orientations of LC molecules to the surface free energy at the interface was ignored. Only J. Cognard used a simple way to measure the surface free energy as the LC molecules were perpendicular and parallel to the interface; however, the relation between the orientations of LC molecules and the surface free energy is still unclear. Based on LCPCF, we here discussed the relation between the orientations of LC molecules and the surface free energy of LCPCF. By designing the experiments, we obtained the surface free energy of the terminal group of the liquid crystal molecule. According to the measurement of surface free energy of LCPCF and the Cassies’s model, the relations among surface free energy of LCPCF, the LC orientations, and applied voltages are calculated. Based on the surface free energy of LCPCF and Creagh’s conception, a phase modulator using LCPCF is also demonstrated. This study helps us developing LCPCF-based devices, such as biosensors, electro-optical switches, and lenses.