Influence of cross-linking density on the structure and properties of the interphase within supported ultrathin epoxy films

Supported polymer film models based on epoxy resin networks with four different cross-linking densities and silica substrates have been established using molecular dynamics simulations. Van der Waals forces in the form of Lennard-Jones 9-6 are applied in calculating the interfacial interactions between the polymer and substrate. The existence of the interphase adjacent to the substrate surface was confirmed by carrying out density profile. Detailed analyses including mean square displacement and radial distribution functions of the structural properties of interphases for the four models were performed and compared. It was found that, with increasing the cross-linking density, the polymer sticks to the substrate more tightly, accompanied by stronger interactions arising from more hydrogen bonds formed between them. Furthermore, the mechanical properties of the interphase were found to be enhanced with the conversion by carrying out tensile deformation. This research regarding the interphase region within supported ultrathin epoxy films will be helpful in understanding the effect mechanism of nanofillers in the epoxy nanocomposites.