Grzegorz Szamel

Grzegorz SzamelProfessor
Office: Chemistry C127B
Phone: 970-491-2795
Education: Ph.D., Warsaw University, Poland

The long-term goal of our research is to be able to predict the macroscopic equilibrium and transport properties of condensedphase systems such as complex fluids using the methods of statistical mechanics. Specific topics of current research include dynamics of polymeric fluids, self-diffusion and vibrational relaxation in liquids, and thermoreversible polymer gelation. One of the unique features of polymer dynamics is the strong dependence of the transport coefficients on the degree of polymerization, N. Similar to what is observed in critical phenomena, the transport coefficients obey scaling laws, e.g., the diffusion coefficient, D scales as N-g where g is the scaling exponent. The strong dependence of the transport properties on the degree of polymerization is attributed to the fact that two polymer molecules cannot cross each other. The current understanding of polymer dynamics is based on a phenomenological “reptation” theory, which assumes that polymers move like snakes. This theory provides estimates of scaling exponents for linear polymer chains that agree with the experimental values. We recently have studied dynamics of ring-like polymers. These molecules, having no heads or tails, cannot move via a snake-like, slithering motion. Therefore, they were expected to exhibit slower dynamics than their linear counterparts. We have found that ring polymers move faster than linear polymers. It seems that faster motion correlates with different conformational statistics: At the same degree of polymerization, ring polymers in the melt are more compact than the linear chains. We also have also started a research project on a new approach to the liquid-state dynamics. Conceptually, most of the current theories of dynamics in liquids originate from the Boltzmann equation. The underlying paradigm of these theories is understanding the dynamics through analysis of sequences of binary collisions. Our approach starts with an oscillatory motion of a particle in its first solvation shell. We expect that at liquid densities, oscillations make a better starting point than free motion and binary collisions. There is a large body of experimental literature on thermoreversible gels of synthetic and natural polymers. However, understanding of the nature of the gelation transition is lacking. We propose to start a major research program aimed at a fundamental understanding of the issues surrounding thermoreversible polymer gelation. We will address the transition itself, the structure and elastic properties of the gel, and dynamic (non-equilibrium) properties of both sol and gel phases.