Coarse-grained molecular dynamics simulations of epoxy resin during the curing process

Abstract

Motivated by the need to establish a multiscale understanding of the mechanical and thermal properties of polymers used for nano-, meso- and macro-composites, we are presenting an investigation of the cross-linking process (associated with curing) of an epoxy phenol novolac and bisphenol-A melt system via coarse-grained molecular dynamics simulations. In particular, we are focusing on the associated structural and physical behaviors of the melts of different cross-linking degree under Couette and Poiseuille flow conditions. At the nanoscale, we also investigated the stress, heat flux and temperature fields that are computable from the quantities of the coarse-grained model of the epoxy resin melt with the extended Hardy’s theory to multibody potentials. We have established that the epoxy resin chains tend to reorient along the direction of the imposed Couette flow, and the degree of alignment increases with the cross-linking degree and shear rate. The pronounced reorientation of cross-linked epoxy resin melts can be ascribed to the inter-bonded chains. This conformational change explains the shear thinning behaviors of cross-linked melts that initiate at low shear rates. The cross-linked melts under Poiseuille flow possess less pronounced velocity profiles, accompanied with the smaller temperature rise from the applied gravity force. Due to the size of the nanoscale channel height, the epoxy resin melts under Poiseuille flow can only be approximately predicted via the continuum theory. We have shown that the discrepancies between atomistic simulations and continuum predictions increase as the wall/epoxy interaction strength reduces. This study reveals the variations of important rheological properties during the cross-linking process and elucidates the roles played by the topological changes in the shear flow, thus can contribute to the design and manufacturing of the epoxy-resin based nanocomposites.