An explanation for the mechanism generating a pretilted nematic liquid crystal conformation aligned on rubbed alkylbranched-polyimide layers is given based on a steric interaction model. An analytical calculation using this model was shown to agree fairly well with the data of torsional coupling strength obtained in this work.

The degree of work done on polyimide films in the rubbing process with a nylon fabric was detected and evaluated in terms of induced birefringence. Strong and weak rubbing (effecting two extremes) gave rise to the optical retardation of 1 degree and 0.1 degree, respectively, with a resolution of 0.1 degree. Generation of a pretilt angle of up to 10 degrees (even up to 30 degrees) for nematic liquid crystals was achieved by performing weak rubbing in a specially synthesized polyimide which was successfully used to fabricate supertwisted nematic liquid crystal displays. Fairly good bistability in a ferroelectric liquid crystal device was obtained by weak rubbing.

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