鄭恪亭

This thesis consists of two main research topics. The first part is with regard to the broadening the reflection band width of cholesteric liquid crystals (CLCs) by using the photo-polymerization of chiral polymer (LC756). The basic concept can be understood as described follows. With the illumination of UV light, the chirality of the LC mixture can be reduced due to the reduction of the amount of un-polymerized chiral polymer. Moreover, during the photo-polymerization process, the pitch length will gradually increase so that the polymerized LC756 can generate polymer network structures to stabilize the changing pitch length. It indicates that the gradient pitch, causing the broadening of the reflection spectrum, can be obtained by the polymerization process. In this part of the experiments, we found that the right-handed chiral polymer (LC756) can effectively stabilize the right-handed CLC filled into a LC cell with suitable cell gap. Experimentally, the optimized reflection band ranges between 556 and 813 nm, whose bandwidth was about 257 nm. Regarding the case of stabilization of left-handed CLCs by right-handed chiral polymer (LC756), the broadening of reflection band cannot be obtained. We infer that the CLC structure of the case of pitch increasing is much uniform than that of pitch decreasing during photo-polymerization processes. The other research topic in this thesis is the photo-polymerization process at different temperature to stabilize CLCs pitch length. Regarding the temperature dependent pitch length of CLCs, if the reflection band of CLCs at high temperature can be polymer-stabilized, the reflection band can be kept when the temperature is cooled down to room temperature. Hence, with regional photo-polymerization, the additive reflection colors in various regions can be applied to broaden the reflection band of CLCs. The cell gap, curing temperature, and material selection are the main keys to achieve such broadening reflection bands of CLCs.