Liquid-crystalline ordering in fluids of semiflexible molecules.

All of the studies described previously have been based on modelling the molecules of a surfactant or liquid-crystalline material by rigid rods. In reality, all such molecules have some degree of internal flexibility. We have begun to investigate including molecular flexibility using density-functional and self-consistent field theoretic (SCFT) methods. So far, we have developed a density-functional theory which accurately describes (in comparison with computer simulation calculations) the nematic-isotropic (N-I) phase transition in an athermal fluid composed of semiflexible hard-sphere chains (see details). This was recently extended to a fluid of so-called "diblock" molecules, each consisting of a rigid and flexible part (see details). In another recent extension, this theory has been generalized to describe smectic ordering (see details).

Another branch of this work employs SCFT on a model of so-called "wormlike" polymers. In our first study, on diblock copolymers each consisting of a rigid and flexible part and considering only excluded-volume interactions between the molecules in a low-density (or 2nd-virial approximation), we showed that the system exhibits a partial-bilayer smectic phase (see details). More recently, this theory was applied to a system of homogeneous polymers, in which a new mechanism for smectic formation in such systems was proposed (see details). Work is continuing to study generalizations of this model, e.g., to go beyond the 2nd-virial approximation.