聚酰亚胺
材料科学
光异构化
异构化
偶氮苯
聚合物
拓本
光降解
辐照
光化学
紫外线
液晶
图层(电子)
光电子学
化学工程
复合材料
光催化
有机化学
化学
物理
核物理学
工程类
催化作用
作者
Hitoshi Sugiyama,Shūichi Satō,Kazukiyo Nagai
摘要
Abstract We review the important features of LC orientation for the alignment layer, namely, production method, alignment mechanisms, and required properties. Photoalignment, which could eliminate the disadvantages of the rubbing method is explored. Applicable materials and techniques for photoalignment are also examined. Many materials for photoalignment layers have been proposed, but polyimide‐based materials are commonly used because of their transparency and insulation properties, which are needed for optical electronic devices. Furthermore, photoisomerization, photodimerization, and photodecomposition as photoalignment methods are reviewed, and specific photoreactive groups and alignment mechanisms are used to induce LC alignment. In summary, polyimides cause photodecomposition and have the following disadvantages; (1) requirement of relatively short‐wavelength ultraviolet (UV) irradiation, (2) difficulty in reorienting polymer chains owing to their rigid polymer matrix, and (3) low‐photo reactivities. The solutions for each disadvantage are already proposed, but the required properties should be determined during material design. Polyimide‐based materials introduced with the azobenzene and cinnamate groups are proposed and found to have the ability of fulfilling the required properties. The mechanism of polyimide photodecomposition is not fully understood. It likely has the advantage in terms of LC alignment stability because of the absence of E/Z isomerization. Therefore, the alignment mechanism and availabilities should be further explored.
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