Effects of the crystallinity of orientation film and mesogenic core of liquid crystals for pretilt angle generation on rubbed polyimide surfaces

The effect of the crystallinity of polyimide (PI) and of the birefringence of the liquid crystal on pretilt angle generation in nematics on rubbed PI surfaces containing thiophenylene moieties has been demonstrated. The induced optical retardation produced in rubbed PI surfaces decreases on increasing the imidization temperature. We suggest that the pretilt angle of 4-cyano-4'-n-pentylbiphenyl (5CB) depends on the crystallinity of the rubbed PI. The order of pretilt angle in NLCs is 5CB > PCH5 ≥ CCH5 at RS ≥ 150 mm (medium rubbing) on rubbed PI surfaces. We suggest that on rubbed PI surfaces the pretilt angle increases with increasing number of phenyl rings in the NLC core.