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Abstract
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.
Acknowledgments
The authors would like to thank the EPSRC and Hewlett Packard for funding this work.