含左右旋手性分子之膽固醇液晶相行為及其光電特性

Abstract

本論文旨在向列型液晶中添加兩種不同旋性對掌性分子混合形成膽固醇液晶，探討具不同濃度之左旋與右旋對掌性分子以及左右旋對掌性分子混合條件下，摻雜濃度與溫度之間的關係及在液晶盒中的光學特性與相變之影響。本研究使用之材料包含向列型液晶E7、左旋對掌性分子S811、右旋對掌性分子R5011。由實驗結果得知，摻雜單一對掌性分子S811於向列型液晶中，隨溫度升高而中心波長藍移（blue shift）；摻雜R5011於向列型液晶中，而R5011具有高螺旋扭轉能（helical twisting power），相對在液晶中所摻雜濃度較少，因此中心波長較不受溫度影響而不移動。另一方面，左旋與右旋對掌性分子混合於向列型液晶中，提升R5011之摻雜濃度，兩種摻雜手性分子之間外消旋作用（racemic effect），引起螺旋解旋，造成中心波段紅移。並透過高精密的LCR測試儀與正交偏光顯微鏡分析液晶相變化，而摻雜單一對掌性分子隨著濃度增加，其膽固醇相範圍越窄；固定左旋膽固醇液晶濃度並增加右旋對掌性分子混合而拓寬膽固醇液晶相。

In this study, the temperature-dependent phase behavior and the optical properties of cholesteric liquid crystal (CLC) containing a nematic host dispersed with a left-hand twist (LT) chiral, right-hand twist (LT) chiral agent and a binary chiral dopant at different dopant concentration were investigated. The materials investigated in this study were prepared by mixing a nematic LC host E7 together with either or both two chiral compounds, the RT chiral agent R-5011 and the LT chiral agent S-811. The experimental results show that by doping single chiral agent S-811 in a nematic host, the central wavelength blue shift as the temperature increased. In the case of RT CLC consisting only of E7 and R-5011, central wavelength was independent to the temperature. This result is presumably due to the temperature dependence of the helical twisting power (HTP) was much lower for R-5011. On the other hand, the central wavelength with binary dopant composed of a RT chiral agent and a LT chiral agent red shifts with racemic effect. We further clarify the phase behavior with a high-precision LCR meter and polarizing optical microscope. We observed a narrower temperature range for cholesteric phase at higher dopant concentration in single dopant case, while the opposite is true for the case when we fix left-handed cholesteric liquid crystal concentration and increase right-handed mixed chiral molecules.