Bulk and surface-induced smectic ordering.

There are many types of smectic liquid-crystalline phases. These occur in both conventional (or "thermotropic") liquid-crystalline materials as well as in amphiphillic systems and copolymers, in the latter cases usually referred to as lamellar phases. The basic characteristic of a smectic phase is a collective organization of molecules into layers. Although widely studied for many years, the particular molecular mechanisms which induce smectic ordering are not well understood. Further questions arise in connection with the effects of surfaces on smectic phases. Many experiments indicate that smectic ordering can be enhanced in the vicinity of a "free surface", i.e., liquid-vapor interface. These surface-induced ordering effects are revealed especially in free-standing films of liquid crystals, which are similar to soap films. We have studied several off-lattice models of thermotropic liquid crystals using mean-field methods in attempts to understand these ordering processes. Particular studies are:

1) Studies of the origins of surface-induced smectic-A ordering at liquid-vapor interfaces and in free-standing films, due to coupling between orientation-dependent intermolecular forces and broken translational symmetry at the interfaces (See details).

(2) Explanations of so-called "layer-thinning transitions" in free-standing smectic-A films based on Landau-de Gennes theory (See details1,2)

(3) Determining the phase boundaries for nematic, smectic-A and smectic-C phases in a model fluid of hard spherocylinders with long-range interactions of quadrupolar symmetry (See details).