Surface oxidation and charge transfer inducing dipole-dipole interactions for homogeneous liquid crystal orientation

Generally, liquid crystal (LC) orientation on rubbed polystyrene (PS) surfaces runs in the direction orthogonal to the rubbing process. In this study, homogeneous LC orientations were produced in the direction parallel to the ion beam (IB) process on PS surfaces using various IB exposure energies. Through x-ray photoelectron spectroscopy it was shown that IB irradiation resulted in the reformation of O=C bonds resulting from surface oxidation or charge transfer, reversely tracing out the produced pretilt angles of the homogeneous LC. Moreover, thermal tests on IB-irradiated PS surfaces were carried out which showed that a relatively high IB exposure energy induced a thermally stable LC alignment property. Finally, we determined the mechanism by which homogeneous LCs are aligned on IB-irradiated PS surfaces with electro-optical properties of twisted-nematic LC cells.