Interfacial fracture between highly cross-linked polymer networks and a solid surface: Effect of interfacial bond density

For highly cross-linked polymer networks bonded to a solid surface, the eff ect of interfacial bond density and system size on interfacial fracture is studied using molecular dynamics simulations. Results for tensile and shear mode simulations are given. The correspondence between the stress-strain c urve and the sequence of molecular deformations is obtained. The failure st rain for a fully bonded surface is equal to the strain necessary to make ta ut the average of the minimal paths through the network from a bonded site on the bottom solid surface to a bonded site on the top surface. At fractio nal interfacial bond densities, cavities form above the nonbonded surface, yielding an inhomogeneous strain profile and a smaller failure strain. The failure strain and stress are linearly proportional to the number of bonds at the interface except in the tensile mode when number of bonds is so few that van der Waals interactions dominate. The failure mode is successfully constructed to be interfacial by limiting the interfacial bond density to b e less than the bulk bond density.