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    Characterizing Two Methods for Achieving Intermediate Surface Pretilt

    Year: 2012

    Journal: Molecular Crystals and Liquid Crystals 2012, 553 (1) pp 81-89, 20121211

    Authors: C. J. Holmes, T. S. Taphouse, J. R. Sambles

    Organizations: School of Physics, University of Exeter, Exeter, EX4 4QL, UK; HP Labs Bristol, Long Down Avenue, Stoke Gifford, Bristol, BS34 8QZ, UK

    Two recipes for controlling the degree of surface pretilt exhibited by the director of the nematic liquid crystals 5CB and ZLI-2293 (Merck) are characterized. The first involves an “overbaked” and rubbed homeotropic aligning polyimide (Nissan SE-1211), and the second uses a rubbed layer of planar aligning polyimide (Nissan SE-130) on top of a homeotropic aligning polyimide (Nissan SE-4811). These allow the director pretilt to be controlled through a range of angles as measured here using the technique of an antiparallel aligned cell doped with a dichroic dye. Results for the “overbaked” Nissan SE-1211 suggest that the degree of pretilt obtained is strongly dependent on the surface upon which the aligning polymer is deposited. Measurements of surface energies using contact angles suggest they have little or no role in controlling the pretilt produced.