Statistical Mechanics of Thermoreversible Gelation

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Grzegorz Szamel is supported by a Faculty Early Career Development Award in the Theoretical and Computational Chemistry Program to develop a theoretical understanding of thermoreversible polymer gelation and the properties of thermoreversible gels. The specific problems to be studied are: 1) existence and properties of a thermodynamic transition underlying the observed gelation transition; 2) structure of the sol and gel phases; 3) elastic properties of the gel phase; and 4) viscoelastic properties of the sol and gel phases. The method to be used is a generalization of a recent statistical mechanical approach to rubber vulcanization (formation of a permanent polymer network) to the case of reversible crosslinking. Specifically, a statistical mechanical theory of chemical association will be used to describe reversible bonding of specific monomers distributed randomly along polymer chains. A replication approach will be used to facilitate averaging over the positions of specific monomers. Finally, an order parameter field (related to frozen density fluctuations) will be introduced, and an effective free energy functional will be derived. The free energy functional will be analyzed using methods similar to those used in the study of the vulcanization transition. The goal of the education plan is to teach students the value and significance of quantitative reasoning in physical chemistry, and chemistry in general. In particular, recitation classes will be introduced into teaching the physical chemistry courses in order to improve student's ability to solve chemical problems using the relevant mathematical formalism. Moreover, a new course on mathematical and computational methods for chemists will be instituted in order to expose students to the applications of numerical and simulational methods in chemistry. Polymer gels have attracted a lot of interest because of the wealth of their potential practical applications. Examples include drug delivery devices, chemical valves and sensors, and magnetic resonance monitoring agents. Their properties can change drastically in response to external stimuli such as temperature, electric field, or light. Szamel's research concentrates on one class of polymer gels, thermoreversible gels. These gels originate from reversible crosslinking of polymeric systems. These gels are reversible, i.e. they liquify upon heating, and are regenerated upon cooling.