Block chemistry for accurate modeling of epoxy resins

Accurate molecular modelling of the physical and chemical behavior of highly cross-linked epoxy resins at the atomistic scale is important for the design of new property-optimized materials. However, a systematic approach to parametrizing and characterizing these systems in molecular dynamics is missing. We, therefore, present a unified scheme to derive atomic charges for amine- based epoxy resins, in agreement with the AMBER force field, based on defining reactive fragments – blocks – building the network. The approach is applicable to all stages of curing, from pure liquid, to gelation, to fully cured glass. We utilize this approach to study DGEBA/DDS epoxy systems, incorporating dynamic topology changes into atomistic Molecular Dynamics simulations of the curing reaction with 127,000 atoms. We study size effects in our simulations and predict the gel point utilizing rigorous percolation theory to accurately recover the experimental data. Furthermore, we observe excellent agreement between the estimated and the experimentally determined glass transition temperatures as a function of curing rate. Finally, we demonstrate the quality of our model by the prediction of the elastic modulus, based on uniaxial tensile tests. The presented scheme paves the way for a broadly consistent approach for modelling and characterizing all amine-based epoxy resins.