Argon Plasma Beam Scanning Processes on Polyimide Films for Liquid Crystal Alignment

Argon (Ar) plasma beam scanning treatments were applied to modify the surfaces of polyimide (PI) films deposited on indium tin oxide glasses in favor of liquid crystal (LC) alignment. LC cells were filled with twist nematic LC (ZLI-2293) on the PI films (Chisso 5310) treated with Ar plasma beam scanning. LC alignment occurs for the as-scanned PI films. The modifications of the PI films were characterized by using atomic force microscope and X-ray photoemission spectroscopy. The grooving mechanism is considered not responsible for the LC alignment. The C 1s, N 1s, and O 1s core level spectra support that Ar plasma beam scanning can induce a bond-breaking process of C=O bonds to create available carbon dangling bonds for the re-formation of C–O bonds. A dipole field is generated through the re-formation of C–O bonds, which may favor the LC alignment via the dipole–dipole interaction.