(184a) Molecular Modeling of Structural and Dynamic Properties of Highly Cross-Linked Epoxy

Cross-linked epoxy is widely used in aerospace and electronics applications. From the viewpoint of molecular simulation, generation of atomistic model structures of cross-linked epoxy at realistic density is a challenging task. We have developed an efficient approach for generating such model structures. The approach relies on using simulated annealing optimization technique for carrying out one-step polymerization of the reaction mixture of epoxy monomers and cross-linker molecules in the simulation box [1]. The technique is computationally efficient and allows for generation of model structure in a day of real time.

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. We implemented molecular dynamics simulations to characterize the structures with respect to their volumetric properties. Specifically, the temperature dependence of density and glass transition temperature were obtained by cooling the structures in a stepwise fashion from 600 K to 300 K. Furthermore, the highly cross-linked nature of these systems leads to different segmental dynamics as compared to the linear polymeric systems. We have used molecular dynamics simulations to study the local chain dynamics in cross-linked epoxy in the vicinity of the glass transition. The chain dynamics of these systems were characterized by their local translational and orientational mobility. Dynamic heterogeneity was also studied by analyzing the spatial distribution of the mobile and immobile atoms in the system near the glass transition.

Reference

[1] Lin, P.H.; Khare, R., Macromolecules 2009, 42 (12), 4319-4327