Molecular dynamics simulation of cross-linked epoxy resin and its interaction energy with graphene under two typical force fields

A model of cross-linked epoxy system composed of bisphenol-A resin, 2,3,6-tetrahydro-3-methylphthalic anhydride curing agent, and 2,4,6-tris(dimethylaminomethyl)phenol accelerator was established and molecular dynamics simulations were performed to calculate the properties of the epoxy and its composites. The results show that the mean square displacement (MSD) and glass transition temperature (Tg) calculated by Dreiding force field are always lower than that by PCFF force field, and the simulation results of Dreiding force field are better consistent with experiments. With the increasing simulation size, total MSD increases while Tg decreases slightly. The simulated systems with DGEBA more than 12 have Tg values similar to experiments. The molecular motion of epoxy system is also influenced by the cross-linking degree, and the presence of uncross-linked particles increases the total MSD. In the graphene/epoxy composites, interaction energy between modified monolayer graphene (MMG) sheets is larger than that between epoxy and graphene, indicating that MMG sheets tend to agglomerate when mixing with epoxy. Functionalization of graphene can reduce interaction energy between MMG sheets and increase that between epoxy resin and graphene, which is beneficial to the dispersion of graphene.