Characteristics and interfacial phenomena pf polyimide alignment layer for liquid crystal display

Abstract

It was investigated the alignment of liquid crystals on a rubbed polyimide alignment layer, which has not been clearly understood yet. It is aimed for the improvement of layer materials and the conventional rubbing technique. Although the alignment of liquid crystal has known to be dominated by the rubbed layer surface, the structural changes of surface resulting from by rubbing has not been fully characterized. Such changes were examined by using several measurement methods; the conoscopy, X-ray diffraction, IR spectroscopy, the contact angle and so on. From the determined changes, the major factors of influencing the alignment of liquid crystal were extracted and an explanation involving them was made upon the rubbed surface. Also, this result was confirmed by applying to LC cells. In the measurement of changes, a devised multiple-coated alignment layers and LB films of PMDA/ODA polyimide and SE150 were used for the high gain of data. The multiple layer was obtained by over-coating one alignment layer on another, in which each layer was made according to the manufacturing sequence of a single alignment layer such as coating, curing, and rubbing. An optical anisotropy of a rubbed polyimide layer for the alignment of liquid crystal was investigated by conoscopic measurement for studying the orientation of polymer chains. Although the layers were over-coated and rubbed, the orientational changes of polymer chains by rubbing were sustained during the over-coating. Following the conoscopies in unrubbed and rubbed layer, the transitional change in the optical anisotropy was observed from the uniaxial to biaxial orientation. Therefore, it was confirmed that the polymer chains oriented due to rubbing and inclined to the film plane. The dichroic ratios of the stretching vibration of $C=0$ group and the X-ray diffraction patterns of multiply coated and rubbed layers of PI alignment film were studied. The orientational change by rubbing was mainly represented from the...