Local Chain Dynamics in Highly Cross-Linked Epoxy near Glass Transition

Cross-linked epoxy is widely used in aerospace and electronics applications. The highly cross-linked nature of these systems leads to different chain dynamics as compared to the linear polymeric systems. In this work, we have used molecular dynamics (MD) simulations to study the local chain dynamics in cross-linked epoxy near the glass transition temperature. The specific epoxy system studied consisted of diglycidyl ether of bisphenol-A (DGEBA) as the epoxy monomer and trimethylene glycol di-p-aminobenzoate (TMAB) as the cross-linker. Well-relaxed atomistic models of cross-linked epoxy were created using recently developed simulated polymerization approach. The glass transition temperature of these model structures was determined from MD simulation by monitoring their volume-temperature behavior in a stepwise cooling run. The chain dynamics of these systems were characterized by their local translational and orientational mobility. Furthermore, dynamic heterogeneity was studied by analyzing the spatial distribution of the mobile and immobile atoms in the system near the glass transition temperature.