Zig-zag walls in the chevron layer structure of smectic liquid crystals: Line energy and selection of the wall orientation

Laboratoire de Physique et de Mécanique des Milieux Hétérogènes, URA 857 du CNRS ESPCI - 10 rue Vauquelin, 75231 Paris Cedex 05, France

Received: 22 January 1998
Accepted: 3 September 1998

Abstract

The cooling of thin cells containing a smectic liquid crystal (layers normal to the plates) often leads to a “chevron": to match the decreasing layer thickness in the bulk with that “frozen" near the plates, the layers tilt and fold in the middle plane of the cell, the two possible chevron directions being separated by walls of typical “zig-zag" shape. A simple model of these walls combines a paper-folding description with qualitative estimates of the folding energy. Different wall orientations are discussed: “thick walls" parallel to the layers, "thin walls" perpendicular to the layers, or inside the zig-zag patterns, slightly inclined with respect to the layer normal of an angle α. A geometrical argument suggests that α is proportional to the layer tilt angle θ, and presumably given by .