Polyimide alignment layer is a very important liquid crystal alignment. The most well-known Liquid crystal display (LCD) alignment methods are homogeneous alignment and homeotropic alignment. This paper research uses different fluff depth and number of rubbing into polyimide,and changes the level of rubbing strength, to observe how electro-optical properties of vertical liquid crystal alignment changes with rubbing strength. By rubbing polyimide with different rubbing strength, this research uses two kind of negative liquid crystal (¡µ£`<0) as samples. This research finds that when rubbing strength increases, the contrast ratio tends to drop.However, the contrast ratio rises after certain level of rubbing strength is applied. Regarding the response time, this research finds that when rubbing strength increases, the response time tends to drop as well. However, the response time rises and falls irregularly after certain level of rubbing strength is applied.

Reflection anisotropy spectroscopy (RAS) is a non-destructive optical technique which can be used to measure the surface properties of sample. We use the technique to detect the optical anisotropy of rubbed polyimide thin film. Atomic force microscopy study of rubbed polyimide showed that rubbing produced microgrooves on the surface of the polyimide thin films, and the surface roughness of the polymer thin films increased slightly with the rubbing strength. Reflection anisotropy signals have been found to be generated on the surface of polyimide thin film on completion of mechanical rubbing, and will increase with an increase in the rubbing strength. We also tried to find out the correlation between RA strength of the polyimide alignment layer and pretilt angle of liquid crystal at the rubbed polyimide films.