Pretilt angle measurements on smectic A cells with chevron and tilted bookshelf layer structures

We have measured the pretilt angle induced by rubbed polymer films in a smectic A and in a nematic liquid crystalline medium using an optical phase retardation method. The pretilt angle was found to depend on the liquid crystalline phase (smectic A versus nematic) and on the smectic layer structure (chevron versus tilted-bookshelf). The occurrence of the different smectic layer structures was verified by X-ray diffraction measurements. The effect of the applied rubbing energy on the pretilt angle obtained is measured.