Photoalignment Behavior on Polystyrene Films Containing Coumarin Moieties

Hyo Kanga* & Daeseung Kangba Department of Chemical Engineering, Dong-A University, Saha-gu, Busan, Republic of Koreab Department of Electrical Engineering, Soongsil University, Dongjak-gu, Seoul, Republic of Korea* Address correspondence to Dr. H. Kang, Department of Chemical Engineering, Dong-A University, Nakdong-Daero 550beon-gil, Saha-gu, Busan, 604-714, Republic of Korea. E-mail: hkang@dau.ac.krWe synthesized a series of polystyrene derivatives containing coumarin side groups, poly(6-(4-vinylbenzyloxy)coumarin)(P6COU#), where # is the molar content of 6-hydroxycoumarin using polymer modification reaction, in order to study the effect of the 6-hydroxycoumarin side groups on the liquid crystal (LC) alignment properties. The LC alignment behavior of these polymers was investigated using photoalignment method. The LC cells made from photoirradiated P6COU# films exhibited homogeneous planar LC alignment with a pretilt angle of approximately 0°. We found that LC aligning ability of the LC cells made from photoirradiated P6COU# films was affected by the molar content of 6-hydroxycoumarin side groups. For example, the azimuthal anchoring energy of a P6COU80 compared to P6COU25 is about 1 × 10−5 J/m2 and 5 × 10−7 J/m2, respectively. The electro-optical characteristics of the LC cells fabricated with P6COU80 films such as voltage holding ratio and residual DC voltage, threshold voltage, driving voltage, and response time were as good as those fabricated from rubbed polyimide films, the most commonly used LC alignment layers.