於受定向摩擦之配向膜上的單分子層液晶之排列狀況

Abstract

本論文主要探討單分子層液晶在定向摩擦配向膜表面上之排列狀況.主要 想了解定向摩擦配向膜而造成液晶定向排列之物理機制.利用不同種類配 向膜分別測量:(1)配向膜經定向所誘發之光相位差與定向強度之關係,以 此決定配向膜分子旋轉重排之程度;(2)利用原子力顯微鏡直接觀察定向前 後之配向膜表面變化;(3)以光二倍頻研究於配向膜上的單分子層液晶排列 與定向強度關係.經由這些實驗發現:[1]定向摩擦造成液晶分子定向排列 最主要由於配向膜分子鍊之旋轉重排,並非因摩擦所產生之微細溝槽造成. [2]單分子層液晶之排列狀況與配向膜分子結構及定向強度明顯相關,其中 主鏈型配向膜分子與具長側鏈型配向膜分子對單分子層液晶之排列傾斜角 表現明顯不同.藉由實驗結果我們提出一微觀之分子模型來加以討論. The molecular alignment of cyanobiphenyl liquid crystal (LC) monolayer by rubbed polymeric surfaces was investigated in this study. The polymeric films used are two types of polyimides. The rubbing-induced optical phase retardation was measured to reveal the surface anisotropy of the polymeric films rubbed with varying unidirectional strength. By combining the phase retardation measurement and atomic force microscopic images of these rubbed polymeric surface, we are able to conclude that the rubbing induced chain alignment on the polymer surface be the major effect in aligning LC monolyers. We further deduce the orientational distribution of the LC monolyer on the rubbed polymeric surfaces from the measured azimuthal second-harmonic intensities. According to these results, the azimuthal distribution of LC molecules was found to be strongly affected by rubbing, while the polar angle was closely related to rubbing strength and the polymeric materials. A simple modle is proposed to elucidate the data obtain from various techniques used.