Visualization of rubbing nonuniformity by double surface treatments of polyimide-coated substrate for liquid crystal alignment

A new method for characterizing rubbing nonuniformity in liquid crystal cells is proposed. Homogeneously aligned cells made by rubbing apparently give a uniform texture under a polarizing microscope. However, nonuniformity of rubbing becomes apparent as scratched patterns, if the rubbing is preceded by rubbing or photoalignment processes. On the other hand, it was found that photoalignment gives quite a uniform texture even on a priori photoaligned surfaces. Thus the double surface treatments along different directions visualize the nonuniformity of rubbing, supplying a tool to examine the condition of the rubbing machine used including buffing cloths.