LANDAU-DE GENNES THEORY OF THE CHEVRON STRUCTURE IN A SMECTIC LIQUID-CRYSTAL

The covariant form of the Landau-de Gennes free energy is used to stud y the chevron structure formed by cooling from the Sm-A to the nonchir al Sm-C phase in a surface-stabilized cell with planar boundary condit ions. We show that the chevron is the thermodynamic equilibrium struct ure. The chevron structure is studied depending on the liquid-crystal elastic properties, temperature, and the surface orientational anchori ng strength. We show that the bistability of the chevron structure res ults from the continuity of the molecular director over the chevron ti p of finite width, and is strongly dependent on the surface orientatio nal anchoring. We estimate analytically the threshold temperature for the chevron formation and show that above this temperature the bookshe lf geometry is stable. We show that the energy of the chevron interfac e follows a power-law dependence on reduced temperature with the expon ent of 3/2.