Surface Morphology of the Rubbed Polyimide and Polystyrene Films and Their Liquid Crystal Aligning Capability

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Abstract
Atomic force microscope (AFM) observation has been made on rubbed polymer films for liquid crystal (LC) molecular orientation such as those of alkylbranched and branchless polyimide (PI) together with polystyrene (PS); other characterizations such as Fourier analysis and roughness evaluation have also been made. It has been investigated how these results of the characterization relate to the LC aligning capabilities such as microscopic texture and pretilt angle. It is shown that in a PI film with alkylbranches there exist grooves owing to strong rubbing, while the branchless does not reveal grooves at the AFM resolution. However, both of them are shown to be capable of aligning nematic (N) LCs very well. Regarding PS film, the grooves run parallel to the rubbing direction but LC alignment is perpendicular to that of rubbing, in accordance with the previous report (D.-S. Seo et al., Jpn. J. Appl. Phys. 31, 2165C 1992)).