定向摩擦與電場誘發液晶配向膜之特性研究

Abstract

本研究試將不同結構之聚亞醯胺經旋轉塗佈後,利用定向摩擦與電 場誘發二種機制,以反平行法製作水平排列的液晶盒.聚亞醯胺的成膜硬化 條件為250℃,1hr.此時亞醯胺化程度可達90%以上.並量測液晶分子於配向 膜上之預傾角及利用原子力顯微鏡觀察定向摩擦與電場誘發二種機制所造 成聚亞醯胺表面型態之改變. 由原子力顯微鏡的觀察確定了細微溝 槽與分子鏈重排效應的產生.不同結構的聚亞醯胺呈現不同的溝槽寬,深度 及分子鏈重排效應.主鏈型聚亞醯胺其產生的預傾角較小(小於1.5度),若 二苯胺上含有氟原子(如HFDAM)可造成較大的預傾角.電場誘發聚醯胺酸偶 極,硬化後確會使聚亞醯胺分子鏈有排列的趨勢,且隨著電場強度的增加其 預傾角亦增加.而定向摩擦之摩擦強度增加其預傾角會減小,直至飽和值. 故可藉由摩擦強度,電場強度的控制達到控制預傾角的目的. In this thesis, we prepared polyimides(PI) from different diamines andtetracarboxylic acids as alignment layers. The precursors of polyimides,poly-amic acids(PAA), were spin-coated on indium-tin oxide(ITO)-coated glasssubstractes. The PI alignment layer were aligned by surface rubbing or bycuring the PI precursors films under an electric field. Liquid crystal cellswere assembled with the anti-parallel rubbing and electric field inducedmethod. The pretilt angle of liquid crystal and the change of polyimide'smorphology were measured using crystal rotation method and atomic forcemicroscope(AFM) respectively. The observation of atomic force microscope identified the existence ofmicrogrooves and the rearrangement of molecular chain. Various structuralfeatures of polyimides showed different depth and width of microgrooves.Besides, it affected the extent of rearrangement of molecular chain. Rigidpolyimides exhibited a smaller pretilt angle(below 1.5°), and the PIcontaining hexafluoroisopropyl group in diamine monomer(HFDAM) could have agreater pretilt angle. Strong electric field had an ability to induce dipolesof polyimides. The increase of electric field strength improved the pretiltangle.Strong rubbing leaded to the decrease in pretilt angle until asaturation value. The pretilt angle of liquid crystals were related to therubbing strength and the electric field strength.