Multiscale modeling of organic-inorganic interface: From molecular dynamics simulation to finite element modeling

ABSTRACTBi-layer material systems are found in various engineering applications ranging from nanoscale components, such as thin films in circuit boards, to macroscale structures, such as adhesive bonding in aerospace and civil infrastructure. They are also found in many natural and biological materials such as nacre or bone. The structural integrity of a bi-layer system depends on properties of both the interface and the constitutive materials. In particular, interfacial delamination has been observed as a major integrity issue. Here we present a multiscale model, which can predict the macroscale structural behavior at the interface between organic and inorganic materials, based on a molecular dynamics (MD) simulation approach combined with the metadynamics method used to reconstruct the free energy surface (FES) between attached and detached states of the bonded system. We apply this technique to model an epoxy-silica system that primarily features non-bonded and non-directional van der Waals and Coulombic interactions. The reconstructed FES of the epoxy-silica system derived from the molecular level is used to quantify the traction-separation relation at epoxy-silica interface. In this paper, two different approaches in deriving the traction-separation relation based on the reconstructed FES are described. With the derived traction-separation relation, a finite element approach using cohesive zone model (CZM) can be implemented such that the structural behavior of epoxy-silica interface at the macroscopic length scale can be predicted. The prediction from our multiscale model shows a good agreement with experimental data of the interfacial fracture toughness. The method used here provides a powerful new approach to link nano to macro for complex heterogeneous material systems.