Adhesion between organic and inorganic materials at nanoscale under the effect of moisture

Organic-inorganic interfaces are found in many natural and biological materials including the mineral-protein system in bone, the bond between a temporary replacement crown and enamel, and the adhesion between marine mussels and various minerals. The structural integrity of these bonded systems depends on properties of both the interface and the constitutive materials. In particular, interfacial delamination has been observed as a major integrity issue. In this paper, a model, which is able to predict the adhesion between organic and inorganic materials, is presented. It is based on a molecular dynamics (MD) simulation approach combined with the metadynamics method, used to reconstruct the free energy surface between attached and detached states of the bonded system. This technique is applied to model the interface between diglycidyl ether of bisphenol A (DGEBA) and silica substrate that primarily features non-bonded and non-directional van der Waals and Columbic interactions. DGEBA is the main adhesive component found in epoxy, which has various engineering applications. It is found that there is a significant reduction of the adhesion between DGEBA and silica when the bonded system is subjected to moisture. This result forms the basis of understanding the deterioration science of composite materials in terms of the durability of organic-inorganic bonded systems when they are used in various engineering applications in which the effect of moisture cannot be ignored.