ATOMIC-FORCE MICROSCOPY OF RUBBED POLYIMIDE ALIGNING FILMS FOR LIQUID-CRYSTAL DISPLAYS

The surface of polyimide (PI) films for aligning liquid crystals were studied by means of atomic force microscopy (AFM). The surface of the unrubbed PI films consisted of polymer clusters of different sizes whi ch are randomly distributed over the film area. After rubbing, however , these polymer clusters formed long chains along the rubbing directio n. The cluster chains were separated with periodicity about 100 nm for weak rubbing strength. Deeper grooves are also present, separated wit h periodicity about 2 mu m that could be related to the microstructure of the fibres from the rubbing cloth. On increasing the rubbing stren gth further on, the cluster chains coalesce into wider ones. The rubbe d PI films show optical retardation, which was increased rapidly with increased the rubbing strength and reached a constant value of about 1 .4nm.