鄭恪亭

論及近幾年顯示器種類，已不再是液晶顯示器獨大的情形，儘管如此，液晶的光學特性與其應用依舊有著不可忽視重要性，如波板、多穩態液晶、及藍相液晶等。尤其近年環保意識抬頭，節能產品不斷出現，液晶智慧窗戶也漸漸倍受重視。 本論文中的研究分為兩部分，第一部分為光控偶氮苯膽固醇液晶，其是由負型液晶摻雜偶氮苯手性分子組成，偶氮苯手性分子會吸收特定波長的光，並使自身結構有順、反式的同分異構化反應，進而使膽固醇液晶之螺距改變，隨著螺距的變化便能將入射線偏振光的偏振方向旋轉一定角度，並研究其在各液晶盒厚度下之線偏振旋轉關係及其線偏振度(degree of linear polarization)，並尋找能夠讓線偏振旋轉90°之液晶盒，再使用1D-DIMOS軟體驗證前述之實驗結果及解釋擬合下的結果，最後觀察其目視效果，依實驗結果推廣到多波長的偏振旋轉，運用實驗結果製作線性偏振旋轉器，並試著設計光閥以應用在液晶智慧窗戶上。 第二部分是製作旋性相互抵消的膽固醇液晶，其由正型向列型液晶摻雜左旋偶氮苯手性分子及右旋手性分子製成，計算兩手性分子的螺旋力(chirality)配製一旋性相消之液晶混合物，又因偶氮苯材料的螺旋力可受光控，便可實現於液晶盒內有水平排列結構與膽固醇平面態兩種排列結構，並在偏光顯微鏡下分別觀察水平排列結構與膽固醇平面態，以及其施加各電場下之光學紋理，證明及解釋各狀態下的結構與排列，最後在前後穿透軸相互正交之偏振片下觀察與第一層液晶長軸夾0°與45°下之目視效果，並依實驗結果設計一液晶智慧窗戶之模型。 In recent years, different types of displays are launched in the market. Liquid crystal display (LCD) is not the only choice for customers. Nevertheless, the importance of optical properties and applications of LCs is unneglectable. Especially, people pay attention to environmental awareness in recent decades. Energy-saving products, such as smart windows, have also been developing in the world. The research topics in this thesis include two sections. The first one is the optically switchable cholesteric LCs (CLCs), made by chiral azobenzene-doped negative nematic LCs. The photoisomerization between trans- and cis-isomers of the azobenzenes can change the pitch length of the CLCs. The variety of pitch length changes the polarization state of linearly polarized lights (LPLs), so CLCs can rotate the direction of the input LPLs by the illumination of light. To reach the target of 90° of the rotation angles of linear polarization, we focused on the rotation angle of linear polarization and the degree of linear polarization by the CLCs with different cell gaps. The experimental results can be theoretically analyzed by the 1D-DIMOS software. Finally, the optically switchable CLCs set between two cross-polarizers can be applied to an asymmetrical light shutter. The second section of the thesis is the study of optically switchable CLCs, made by left-handed chiral azobenzene and right-handed chiral dopant-doped positive nematic LCs. Due to the photoisomerization of the left-handed chiral azobenzene, the helical twisting power (HTP) can be decreased by shinning with UV light to photoisomerize the trans-isomers to cis-isomers. Moreover, the effective HTP of the chiral dopants with opposite chiralities can be canceled out with the proper selection of their concentrations, so that the CLCs can be switched to homogeneous alignment textures. On the other hand, the initial homogeneous alignment textures can be switched to planar textures of CLCs by the illumination of UV light to increase the chirality. Here, studies of the two different arrangement structures of LCs, the corresponding T-V curves, and their structures applied with various electric fields observed under a polarization optical microscope will be given. Finally, the view through the optically switchable CLCs between cross-polarizers with β angles of 0° and 45° will also be demonstrated to achieve an asymmetrical smart window.