Surface free energy of chosen polyimides used for alignment of liquid crystals

Abstract

According to classical method polyimides were obtained in two-step polycondensation process via 10% solutions of poly(amic acid)s in dimethylformamide (DMF). The indium tin oxide (ITO)-glass plates or glass plates were spin-coated with the 1% (w/w) poly(amic acid)s solutions and then the solvent was evaporated. The aligning polyimide layers were prepared by thermal imidization. Polyimide layers on indium tin oxide (ITO)-glass plates were prepared by thermal imidization at 250°C for 4 h. Their surface free energy and its components were determined. Polyimide films on soda glass with various degree of imidization were prepared by thermal treatment at 180°C, 200°C, 220°C and 250°C. Evaluation of rubbed polyimide layers wettability by four nematic liquid crystals (5CB, 6CB, 6CHBT and 8CHBT) was carried out.