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Surface and interface designs in side-chain liquid crystalline polymer systems for photoalignment

Abstract

In side-chain liquid-crystal (SCLC) polymer systems, the liquid crystalline (LC) mesogenic groups preferentially orient normal to the substrate plane due to the excluded volume effect (homeotropic alignment). Photoresponsive azobenzene (Az) mesogens have a transition moment parallel to the molecular long axis. Light irradiation for photoreactions is generally applied perpendicular to the film surface. Therefore, a homeotropic orientation inhibits efficient photoreactions and photoalignments in Az SCLC polymer systems. This review focuses on new approaches to induce a random planar orientation in Az SCLC polymer systems by interface and surface molecular design. The mesogens in a high-density SCLC polymer brush formed by surface-initiated living radical polymerization adopt a random planar orientation. In the film of an SCLC block copolymer with an amorphous block, a random planar orientation is induced via surface segregation of either of the blocks. The random planar orientations of SCLC polymer systems are thermally stable and offer efficient in-plane photoalignment and photoswitching with hierarchical LC molecular architectures, forming, e.g., microphase-separated (MPS) SCLC block copolymers and layered polymer LC systems. These surface and interface molecular designs are expected to provide new concepts and possibilities for LC polymer devices.

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Acknowledgements

I thank Professor Takahiro Seki of Nagoya University for his encouragement, kind expostulations, understanding, and consideration of my study. I also acknowledge the support provided by Associate Professor Yukikazu Takeoka and Assistant Professor Mitsuo Hara of Nagoya University for their kind support. I am thankful for the significant experimental efforts and results of Dr. Takayuki Uekusa, Dr. Yuichi Morikawa, Dr. Hafiz Ashraful Haque, Mr. Yusuke Koizuka, Mr. Tomoya Murase, Mr. Kenjiro Imai, Dr. Masami Sano, Dr. Kei Fukuhara, Mr. Yuki Nagashima, Mr. Koji Mukai, and many graduate students in our laboratory at Nagoya University. The real-time in situ GI-SAXS observation studies involved collaborative work with Dr. Yuya Shinohara of the University of Tennessee and Professor Yoshiyuki Amemiya of the University of Tokyo. This work was supported by a Grant-in-Aid for Scientific Research (B: 25286025, S: 16H06355) from JSPS, the PRESTO Program from JST, Toyo Gosei Memorial Foundation.

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Nagano, S. Surface and interface designs in side-chain liquid crystalline polymer systems for photoalignment. Polym J 50, 1107–1119 (2018). https://doi.org/10.1038/s41428-018-0100-4

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