| dc.description.abstract | 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. | en_US |