Molecular Modeling of Silica-Epoxy Interphase with Monolayer Silane

Abstract

In this study, the interactions of epoxy-amine resin with the silica surface in the presence of monolayer silane is studied using molecular dynamics (MD) simulations. First we deposit glycidoxypropyltrimethoxy silane (GPS) on the silica surface at different densities and react the GPS molecules with the silica surface through a condensation reaction. A mixture of Epon828-Jeffamine® D-230 is then put on the silica surface and equilibrated to predict the epoxy-amine diffusion into the monolayer silane using the general AMBER force field. Epoxide-amine curing reaction among the epoxy, silane and amine are modeled using the cross-linking algorithm. The model is then loaded in Mode-I and Mode-II with the reactive force field ReaxFF to predict the stress-strain responses and failure loci within the interphase. Simulation results indicate that as the number density of silane increases, proximity of the epoxy and amine molecules with the silica surface decreases; this is because increased silane density leads to less open space for diffusion to the silica surface. However, an increase in the silane density increases the covalent bonding interactions in the interphase. As results, interphase strength improves with the increase of the silane density on the silica surface and approaches the bulk epoxy properties. Damage mode changes from adhesive to cohesive with the increase in silane density on the silica surface.