The effect of rubbed polymer films on the liquid crystal alignment

Abstract

The observation of surface profiles on rubbed polymer films demonstrated that micro-grooves had been formed on the polymer surface. on the other hand, the infrared (I.R.) and U.V.-visible dichroic measurements of the rubbed polymer films have revealed that the polymer backbone chains are oriented parallel with the rubbing direction. We determined whether micro-grooves or polymer chain orientation causes the alignment of liquid crystal (LC) molecules. It was found in polystyrene (PS) films that LC molecules aligned perpendicular to the rubbing direction, although there were micro-grooves whose direction was the same as a rubbing direction. It was also found that the rubbed polyimide (PI) films lost LC alignment ability when they had been covered with Pt-Pd films about 30 Å thick, even though micro-grooves were still present. The experimental results imply that LC molecules are aligned by the effect of the orientation of the polymer chains on a rubbed polymer surface.