摩擦配向角度對於橫向螺旋態光軸及膽固醇液晶光電特性之影響

Abstract

本論文探討配向角度對於膽固醇液晶橫向螺旋態光軸之排列與光電特性。本研究是以摩擦法對基板進行表面處理，並合成多種配向角度之空液晶盒，在注入膽固醇液晶後，利用電流體效應形成橫向螺旋態，透過穿透光譜與觀察光學紋理，判斷不同配向角度之液晶盒在橫向螺旋態時的光軸變化。由實驗結果得知，光軸之角度變化受到配向角度所控制，且光軸之夾角為配向角度之二分之一倍。此外討論配向角度對於膽固醇液晶之平面態、橫向螺旋態時之對比度與高頻時臨界電壓之影響，實驗結果得到以上三者並不會受到配向角度的影響。最後介紹由本實驗室團隊首先發現之一種新穎形成橫向螺旋態的方法，初步結果顯示當液晶盒之配向角度在90度時，可得到最佳的橫向螺旋態，當配向角度逐漸提高，橫向螺旋態之缺陷也逐步增加，當配向角度大於120度後，此時便無橫向螺旋態紋理之產生。

In this thesis, the optical axis (O.A.) of the uniformly lying helix (ULH) state and electro-optical properties of the cholesteric liquid crystal (CLC) cells with distinct rubbing angles were investigated. Planar-aligned CLC cells with various rubbing angles were fabricated using the conventional mechanical rubbing method. The ULH state was formed by means of the electrohydrodynamic effect after the CLC solution was injected into an empty cell. Both the measurement of transmission spectra and the observation of polarizing optical textures were carried out for each CLC cell to identify the effect of the rubbing angle on the O.A. of the ULH state. Experimental results suggest that the O.A. of the CLC cell in the ULH state can readily be controlled by the rubbing angle. That is, the angle between the rubbing direction and the O.A. of the cell in the ULH state is equal to half of the rubbing angle. In contrast, our results imply that the rubbing angle is insignificant to modify the optical profiles of the planar state, the contrast ratio in the ULH state, and the threshold voltage of the cell driven by high frequency voltages. Finally, referring to a new approach for the formation of the ULH state proposed by our group, preliminary results indicate that an optimum ULH state is observed in 90 degrees twisted CLC cells whereas the ULH texture is suppressed in cells with rubbing angles larger than 120 degrees. When the rubbing angle is set between 90 degrees and 120 degrees, the number of defects formed in the ULH state is increased with increasing rubbing angle.