Molecular understanding of the adhesive force between a metal oxide surface and an epoxy resin: Effects of surface water

A mechanism of the adhesion interaction between an aluminum oxide surface and an epoxy resin is investigated by using density-functional-theory (DFT) calculations. To understand effects of adsorbed water molecules on the adhesion interaction, hydroxylated aluminum oxide surfaces with adsorbed water molecules are prepared. Geometry optimization is performed for a model of adhesiveadherend complex, which is comprised of a fragment of epoxy resin and a wateradsorbed aluminum oxide surface. DFT calculations demonstrate that hydroxy groups and ether groups of epoxy resin can interact with the adherend surface via a hydrogen-bond network of adsorbed water molecules, which leads to a critical factor in the adhesion interaction. Plots of energy versus vertical distance of the resin from the surface are nicely approximated by the Morse potential. The force required for detachment of the resin from the surface can be estimated from the maximum value of the forcedistance curve, which is obtained from the derivative of the potential energy curve. Obtained results demonstrate that the hydrogen-bond network via adsorbed water molecules significantly affects the adhesion mechanism. The adsorbed water molecules provide a long-distance adhesion interaction but exert little influence over the maximum value of the adhesion force.