Polyimides photoalignment

Fig. 3.12 Polyimide with fluorine atoms that shows high tilt angle photoalignment.

In this method, radicals generated by the UV exposure connect to other parts of molecules and generate a new structure. If this type of material shows a preferred photoalignment, then this new structure can be used to align the LC. This type of photoalignment was found in the benzophenone structured polyimide shown in Fig. 3.9 [32]. 

M. Hasegawa and Y. Taira, Nematic homogeneous photoalignment by polyimide exposure to hnearly polarized UV. Journal of Photopolymer Science and Technology 8, 241 (1995). 

D.-S. Seo and J.-M. Han, Generation of pretilt angle in NLCs and EO characteristics of a photoaligned TN-LCD with oblique non-polarized UV light irradiation on polyimide surface. Liquid Crystals 26, 959 (1999). 

K. Sakamoto, K. Usami, T. Sasaki, Y. Uehara, and S. Ushioda, Pretilt angle of liquid crystals on polyimide films photoaligned by single oblique angle irradiation with unpolarized light. Japanese Journal of Applied Physics 45, 2705 (2006). 

J. Y. L. Ho, V. G. Chigrinov, and H.-S. Kwok, Variable liquid crystal pretUt angles generated by photoalignment of a mixed polyimide alignment layer. Applied Physics Letters 90, 243506 (2007). 

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