Abstract
The microscopic surface and physical mechanism generation in nematic liquid crystalline 5CB (4-n-pentyle-4’-cyanobiphenyl) on three kinds of rubbed polyimide surfaces were investigated. We compare different rubbing configurations with respect to their rubbing work, the resulting plastic deformation of the surface, and the homogeneity of the liquid crystalline alignment. The orientation of liquid crystalline molecules on rubbed polymer surfaces is characterized by the physical and chemical properties of the polymer and liquid crystalline material as well as by the coating and rubbing technique used. The effect of the rubbing work applied to polymer-coated substrates on the birefringence was AL-1051 (0.103)>AL-8044 (0.094) > PMDA- ODA (0.085) or the oriented birefringence was AL-1051 (0.100)>AL-8044 (0.092) >PMDA-ODA (0.083). Atomic force microscopy was utilized to investigate the surface conformation of the three-polyimide alignment layers before and after rubbing. With increasing rubbing strength, the molecular alignment varied greatly. The director of molecules with positive dielectric anisotropy was uniform and had a pretilt angle determined by the molecular structure. The simple method enabled us to give the value of pretilt angle.