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Thursday, October 22, 2009
3:30 PM - 4:30 PM
CNLS Conference Room (TA-3, Bldg 1690)

Seminar

Thermoreversibly Associating Polymer Networks with Variable Chemical Kinetics

Robert Hoy
Yale University

Thermoreversible polymer networks, intermediate between classical rubber and polymer melts, have fascinating dynamical and mechanical properties and show great potential as "smart" materials. However, outside of certain "simple" regimes, their dynamics are poorly understood. We develop a simulation protocol for studying these systems under arbitrary conditions. Our model is based on an extension [1,2] of the Kremer-Grest bead-spring model, and the simulation method is a hybrid of molecular dynamics and Monte Carlo. We carefully validate the model and method for quiescent, equilibrium conditions. Sticky bond lifetimes are mappable to a two state Arrhenius model with simple chemical kinetics. We then examine the quiescent (and heterogeneous) dynamics of the constituent polymer chains, nonequilibrium chemical dynamics of the sticky bonds, and bulk mechanical properties. The model is effective in separating the effects of thermodynamics and chemical kinetics on all of these. Many of our results are nontrivial and heretofore unreported, but may be understood in terms of the crossover from diffusion-limited to kinetically-limited sticky bond recombination, which both influences and is influenced by polymer physics, i. e., the connectivity of the parent chains. Relations to recent and ongoing experimental work will be discussed.

1. “Thermoreversible Associating Polymer Networks: I. Interplay of Thermodynamics, Chemical Kinetics, and Polymer Physics", Robert S. Hoy and Glenn H. Fredrickson, cond-mat/0908.1822.

2. "Kinetics and dynamic properties of equilibrium polymers”, C. C. Huang, H. Xu, and J. P. Ryckaert, J. Chem. Phys. 125, 094901 (2006).

Host: Turab Lookman, LANL