封閉柱狀液晶樣品於外加電場下之分子場穩定性及光學特性

Abstract

本論文研究封閉式柱形線狀液晶樣品於外加電場下的導向矢排列穩定性及 其光學特性。我們針對內含負性介電各向異性線狀液晶的錐柱腔及正圓柱 腔來討論，同時邊界上的液晶指向矢皆成垂直腔壁之狀態。理論上我們預 測在錐柱腔中受外加電場及液晶彈性常數的影響。可以有五類分子場轉換 序列存在。在正圓柱腔中受外加電場及外觀參數的影響，線狀液晶MBBA會 有三類分子場轉換序列存在。實驗上，我們製備了錐柱腔含負性介電各向 異性的線狀液晶樣品，並使液晶分子垂直於腔壁。在正交偏光顯微鏡下觀 察記錄外加電壓對光學圖像的影響，並與理論預測相互驗證。 We report the study on the director-field transition induced by electric field in a closed cylindrical cavity of nematic liquid crystal (NLC) with negative dielectric anisotropy. The closed conical cavity and the closed regular cylindrical cavity are used to demonstrate the stability of director fields and optical properties. The directors of NLC are forced to be strong anchoring on the boundaries of cavity. The electric potential is applied along the symmetry axis of the cylindrical cavity. The dependency of the stability and transition sequence of sequence of director field on bulk elastic constants are demonstrated in the case of closed conical cavity. The dependency of the stability of director field and the transition voltage on the aspect ratio are also investigated in closed regular cylindrical cavity and closed conical cavity. In experiment, we have prepared the closed conical cavities of NLCs. Using the polarizing microscope, we observe the transitions of optical patterns induced by electric field as the prediction of theory.