Liquid crystal orientation mechanism and tilt angle transition behavior on homeotropic polymer surfaces due to ion beam treatment

We examined the transition behavior of the tilt angle on homeotropic polyimide (PI) surfaces as a function of ion beam (IB) irradiation incident angle. We also investigated the liquid crystal (LC) orientation mechanism by X-ray photoelectron spectroscopy. The tilt angles of the IB-irradiated PI surfaces were controlled in the range of 82-90° as functions of IB irradiation time and incident angle. The largest deviation from the homeotropic alignment was achieved at an IB incident angle of 45°. The plot of the atomic percentage of C-O binding energy versus IB incident angle was shaped like an upward-pointing triangle, while that of the C=O binding energy versus IB incident angle was the reverse. The tilt angle behavior as a function of IB incident angle was similar to the atomic percentage behavior. The LC alignment with IB irradiation was due to the dipole-dipole interaction between the C-O single bonds and the LC molecules. An excellent voltage-transmittance curve for the vertical alignment (VA)-LC cells was observed with a threshold voltage behavior related to the tilt angle. Suitable response time characteristics were measured for VA-LC cells treated with IB irradiation