PRETILT ANGLE MEASUREMENTS ON SMECTIC-A CELLS WITH CHEVRON AND TILTEDBOOKSHELF 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 optica l phase retardation method. The pretilt angle was found to depend on t he Liquid crystalline phase (smectic A versus nematic) and on the smec tic layer structure (chevron versus tilted-bookshelf). The occurrence of the different smectic layer structures was verified by X-ray diffra ction measurements. The effect of the applied rubbing energy on the pr etilt angle obtained is measured.