Photoalignment of liquid crystals by a covalently attached self-assembled ultrathin film |
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| Authors: | Lingli Zhang Xiudong Sun Yongjun Liu Zenghui Peng Li Xuan |
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| Institution: | 1. Department of Physics , Harbin Institute of Technology , Harbin , China zhangcbzpp@163.com;3. Department of Physics , Harbin Institute of Technology , Harbin , China;4. College of Science, Harbin Engineering University , Harbin , China;5. State Key Laboratory of Applied Optics, Changchun Institute of Optics Fine Mechanics and Physics, Chinese Academy of Sciences , Changchun , China |
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| Abstract: | In this paper, the polyanion-containing cinnamoyl group (PACSS-CF3) was self-assembled with diazoresin (DR) to form a kind of stable covalent ultrathin film by irradiation with 365?nm UV light. The photoalignment properties of the DR/PACSS-CF3 covalent film were investigated. The covalent film was found to have anisotropy after irradiation by 297?nm linearly polarised ultraviolet light (LPUVL), and could induce uniform alignment of liquid crystals (LCs). The pretilt angle of the LC was 2.5°. The stability of the film was enhanced by the covalent bonds. The films were thermally stable to 180°C. Polarised UV-Vis spectroscopy was utilised to investigate the photochemical process of the covalent film. It was found that cinnamoyl moieties parallel to the polarisation direction of the LPUVL were consumed by the photoreaction faster than those perpendicular to the polarisation direction. It can be concluded that the selective photoreaction induced the anisotropy of the films. The anisotropic films induced the homogeneous alignment of LC. |
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| Keywords: | covalent ultrathin film photoalignment liquid crystal pretilt angle |
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