Donald E. Sullivan

My work has focused on the nature of the interactions between molecules of these systems which can produce such LC phases, most recently in polymers. In particular, I have concentrated on the effects of so-called “excluded-volume” interactions, which basically result because the presence of a molecule excludes any other molecules from occupying the same space and are always present regardless of any other types of interactions. The statistical description of these systems is complicated due to the fact that polymeric molecules are flexible or “wiggly”, i.e., cannot be simply pictured as straight pencils, which leads to several mathematical complexities. Recently, I have studied two models, both in the framework of what is called “self-consistent field theory”. One is a discrete model, in which a polymeric molecule is constructed from a chain of hard-sphere beads. The other model is a continuum version of the first one, what’s called the “wormlike-chain” model, in which the polymers are pictured as flexible strings. The approaches to solving the theory for these models rely heavily on numerically-intensive computational techniques, facilitated in large part by SHARCNET. The two models yield complementary information on aspects such as dependence of phase boundaries, i.e., the relation between density and pressure, on properties such as the length-to-width ratio of the molecules and their degree of flexibility. Besides polymers, one other type of system to which these studies have been successfully applied is aqueous suspensions of certain viruses.