無偏振片之高對比與低壓液晶模態

Abstract

我們選用可消旋的旋光性材料製作高分子穩定型膽固醇液晶元件(PSCT)，藉由加熱讓消旋材料失去旋光性，消旋後液晶受到的彈力位能(elastic energy)減弱，可有效降低元件的臨界電壓與反應時間。由於聚合物形成的高分子網狀結構對液晶存在錨定力，消旋後的液晶受到錨定力的束縛會有膽固醇液晶的排列趨勢，因此消旋後元件的對比度能接近未消旋前的大小。此外，當元件處於部分消旋的狀態時，元件內會同時存在不同螺距的膽固醇液晶結構(gradient pitch)，這將有助於對比度的提升，此時臨界電壓的大小會介於完全消旋與未消旋之間。 本研究主要討論液晶主體、紫外光強度、液晶盒條件、旋光性材料與聚合物濃度等因數對元件光電特性的影響，並找出最佳的實驗參數。在適當的條件下，元件經過完全消旋後可降低30~40%的臨界電壓，在部分消旋狀態下，元件最高的平均對比度可高達12.3:1。

The recemizable chiral dopant was applied in the reversed-mode polymer-stabilized cholesteric texture (PSCT). The chiral dopant was racemized by thermal process, the elastic energy from the chiral dopant would be reduced, this will cause lower threshold voltage and fast response time. Due to the anchoring effect of the polymer network on the LC molecules, the LC would tend to become the CLC structure even if the chiral dopant has been fully racemized. The contrast ratio is maintained as the initial value. Additionally, the CLC structure presented gradient pitch during the racemization process and resulted in higher contrast ratio, in this time, the operating voltage was operated between the one fully racemized and without racemized. In this thesis, the influence of LC host, UV intensity, cell condition, chiral dopant and polymer concentration on electro-optical properties are discussed. Under appropriate conditions, the PSCT devices decrease the 30~40 percent threshold voltage when chiral dopant fully racemized. The contrast ratio can be achieved 12.3:1 when chiral dopant is partially racemized.