TEMPERATURE-VARIATIONS IN THE DIRECTOR ORIENTATION AND ANCHORING ENERGY AT THE SURFACE OF CHOLESTERIC LAYERS

Slight changes with temperature in the director orientation at the sur face of a perfect planar cholesteric liquid crystal (CLC) layer, which are precursors of a jump in the pitch of the cholesteric helix, are o bserved by measuring the temperature dependence of the optical transmi ssion spectra of the layer. The observed changes in the director orien tation are described in the framework of the continuum theory of CLCs, supplemented with allowance for the surface anchoring forces. In part icular, the angle of deviation of the director at the surface from the alignment direction at the exact temperature of the jump in pitch is expressed in terms of the anchoring potential. The relation obtained i s use to find the anchoring potential in the samples. (C) 1996 America n Institute of Physics.