Influence of the inhomogeneous surface pretilt on zig-zag defects

The influence of the inhomogeneous surface pretilt (slope) on chevron struc tures and on zig-zag defects in a SmC liquid-crystal cell is studied. The e xperimentally observed effect of the confining substrate with controlled va riation of the surface slope on the formation of zig-zag defects is qualita tively explained with the Landau-Ginzburg-type free-energy expanded in term s of the nematic director field and the smectic complex order parameter. Tr ansitions in the C1 and C2 chevron structures are studied as functions of t he surface pretilt angle theta(t). The threshold conditions are calculated. The width of the straight element of the domain wall (running parallel to the smectic layers) and the costs for its formation are estimated. (C) 1998 American Institute of Physics. [S0021-8979(98)03920-6].