Effect of Chemical Structures of Polyimides on Unidirectional Liquid Crystal Alignment Produced by a Polarized Ultraviolet-Light Exposure

Unidirectional liquid crystal (LC) alignment produced by a polarized ultraviolet-light (UV) exposure was examined using various polyimides (PIs) which consist of different tetracarboxylic dianhydrides and diamines. The photosensitivity and anchoring energy of the LC alignment as a function of UV dosage are summarized with respect to the chemical structures of the PIs. The results suggest that the UV absorption efficiencies, molecular conformations, mechanisms of decomposition, and anisotropic van der Waals forces of the PIs largely affect the photoalignment properties of the LC.