Surface properties of rubbed polyimide for alignment of liquid crystal

The surface tensions with the structural changes in the alignment layer surface due to rubbing was compared with the curing temperature and the rubbing strength. At low curing temperature, the polar component of surface tensions had a high contribution, but at high curing temperature, the dispersion component was greater than the polar components. These indicated that the surface cured at high temperature were less polar than those at low temperature, while, rubbing resulted in the larger polar component and induced the ordering of polar groups on the surface in the X-ray measurement. Then, the ordering of polar groups in the rubbed surface could be conjectured to play an important role in the alignment of liquid crystals from the fact that the layer with a high dispersion component also aligned liquid crystals along the rubbing direction.