Molecular dynamics simulation study of reactive encapsulation of solvent in epoxy curing

A series of the molecular dynamics simulations was performed for constructing atomistic models of cross-linked polymer networks and predicting their material properties. Systems comprised of Epon828 epoxy resin and Jeffamine-D400 diamine curing agents were modeled and cured with varying amount of dichloromethane (DCM) solvent (0-40 wt%) using a multi-step algorithm. The cross-linked networks successfully achieved to 100% cross-linking yield. After cure, the DCM was removed from the crosslinked systems. The systems were then annealed to an equilibrium density. Mechanical (Young's modulus), thermal (glass transition temperature), and structural (mass density, radial distribution functions, dihedral angle distribution functions, and minimum contour path length distributions) properties were calculated. These properties were then compared with the results measured in actual epoxy systems created by "Reactive Encapsulation of Solvent". All properties except for minimum contour path length of nitrogen-nitrogen (N-N) linkages were insensitive to the initial amount of solvent. These findings are consistent with the experimental results. The major simulation finding thus far was that the minimum contour length of N-N linkages was altered by the initial amount of the solvents despite intermolecular packing being indistinguishable among the different systems. This implies that both the network topology and large-scale material properties such as toughness could be altered and influenced by the amount of solvents. The simulations will provide an alternative way of exploring the cured thermoset polymer materials, predicting the material properties and understanding the material behaviors according to the initial amount of solvents.