Alignment of Nematic Liquid Crystal(5CB) on the Treated Substrates: Characterization of Orientation Films, Generation of Pretilt Angles, and Surface Anchoring Strength

Abstract This article provides a review on the experimental aspects of the alignment of nematic liquid crystal (NLC) in the pretilted homogeneous form in the sandwich cells; most of the contents of this paper are the results of research done by the authors in these few years. For simplicity and convenience, we used nematic liquid crystal (5CB) only; however, we have explored several polymer orientation films such as alkylbranched or alkylbranchless polyimide (PI), PI-Langmuir-Blodgett (LB) films, and those of polypyrrole. All these films were rubbed prior to assemble the cells except for some cases of PI-LB films. These films were characterized in terms of the atomic force microscope (AFM) observation and the optical retardation that are induced by the rubbing or unidirectional pulling up of the substrates in the LB process. Aligning capabilities of these orientation films for 5CB have been evaluated in terms of the texture of the NLC media, generation of pretilt angles, and temperature dependence of the anchoring strength (energies). Some results of this investigation is thought to partially contribute to provide several practical techniques for LCD technologies and to have some understanding the complicated surface anchoring phenomena. Key Words: polyimide (PI) filmsPI-Langmuir-Blodgett (LB) filmsrubbing strengthoptical retardationpretilt angleatomic force microscope (AFM)extrapolation lengthpolar anchoring energy