Local Chain Dynamics and Dynamic Heterogeneity in Cross-Linked Epoxy in the Vicinity of Glass Transition

We studied the local chain dynamics as well as the dynamic heterogeneity in highly crosslinked epoxy near glass transition by molecular dynamics simulation. In previous work (Lin and Khare in Macromolecules 2009, 42, 4319), we had reported creation of fully relaxed atomistic structures of cross-linked epoxy; the glass transition temperature of these structures was also determined from volume temperature behavior. The local chain dynamics in these structures is characterized by using molecular dynamics simulation in this work. Local translational mobility of cross-linked epoxy as measured by mean-squared displacement of atoms exhibited two subdiffusive regimes within the simulation time of 200 ns. Local orientational mobility was determined by monitoring the autocorrelation function (ACF) of a vector associated with the epoxy monomer. Time dependence of an order parameter based on this ACF showed that there was almost no orientational relaxation when the temperature was near or below g