- 學位論文
螺距與電壓對液晶迴流效應之影響
Influence of Pitch and Voltage on Liquid Crystal Backflow Effect
摘要
液晶同時具有固體之有序排列性與流體之流動性，液晶的流動與指向矢的轉動會互相耦合影響，形成一些獨特的現象。例如扭轉向列型液晶盒，在瞬間關閉高電壓下，會有光學跳躍的現象產生。由於此流動效應的影響，使得液晶分子需要較長的反應時間，我們將此效應稱之為迴流效應(Back-flow effect)。 本論文分兩個部分。第一部分研究在扭轉向列型液晶盒中，固定液晶盒厚度(d)，探討改變不同的螺距(p)的液晶對液晶迴流效應之影響。由模擬中得知d/p值越大，閥值電壓也越大，但光學跳躍的現象則會越來越微弱。我們進一步分析指向矢和流速分佈與反應時間之關係。最後做出實驗樣品，驗證模擬與實驗之結果。 第二部分探討，在不同模態的液晶盒中之Back-flow電壓(VBF)，VBF原定義是在施加不同電壓於垂直排列型液晶盒中，因為液晶分子受到流動效應影響，反應時間曲線大幅度增加時之轉折點電壓值。模擬結果顯示，在垂直排列型液晶盒、對掌性垂直排列液晶盒都存在著VBF，並且與液晶盒厚度有關。但是在扭轉向列型液晶盒中，VBF並不存在著。
並列摘要
Liquid crystals (LCs) have both ordered aligned character of solid and flow property of fluid. The coupling interactions between the flow and rotation of LC molecules, which is called flow effect, lead to some peculiar phenomenon. For example, when a high voltage is suddenly switched off in the twisted nematic liquid crystal cell (TN LC cell), the back-flow effect results in an optical bounce, and the response time is much longer than usual. This paper is divided into two parts. In the first part, we investigated the back-flow effect in the TN LC cell by varying the pitches (p) of the LC and fixing the cell thickness (d). The optical bounce decreases and the threshold voltage increases when the d/p ratio was increased. We also analyzed the influence of flow and director distribution on the response time. Finally, we confirmed these simulation results by experiments. In the second part of this study, we investigated the back-flow voltage (VBF) of varied LC modes. Due to the back-flow effect, the response time is increased significantly at an applied voltage of VBF in the VA LC mode. VBF can also be found in the chiral VA LC mode, but not in the TN mode. And its value is cell thickness dependent.