MELTED-GRAIN-BOUNDARY PHASE IN CHIRAL SMECTIC-C LIQUID-CRYSTALS NEAR THE TRIPLE N-ASTERISK-A-ASTERISK-C-ASTERISK POINT

A new melted-grain-boundary (MGBC) phase is predicted in chiral smectic- C (Sm- C) liquid crystals close to the triple N*A*C* point. This phase consists of Sm- C slabs, with smectic layers tilted to the pitch axis x. The director n(x) in each slab turns around the smectic wave vector q almost on the cone =0, the Sm- C equilibrium inclination angle. The smectic order melts on the plane of the grain boundaries between the slabs instead of on dislocation lines. We show that the MGBC phase has lower energy than the previously proposed twist-grain-boundary (TGBC) phase. The MGBC model agrees better than the TGBC one with some recent experimental data. © 1995 The American Physical Society.