Unveiling the Chemical Reactions Involved in Moisture-Induced Weakening of Adhesion between Aluminum and Epoxy Resin

Abstract

The adhesive bonding of metals using epoxy resin is an important technology in manufacturing industries. It is well known that adhesion strength becomes significantly reduced in a moist environment. To understand the mechanisms at the electronic structure level, we perform atomic dynamics simulations on various Al and epoxy resin interface systems with water molecules inserted in the contact region. In accordance with experimental conditions, the Al layer is surface-oxidized to a depth of 10 Å while the bisphenol A type epoxy molecule has both OH and ether groups. Shear deformations are simulated using the hybrid quantum-classical method in which about 1500 atoms at the contact region are treated with density functional theory. For the first time, calculated adhesion strengths compare well with the experimental values. Three types of chemical reactions that affect the adhesion strength occur depending on the terminal functional groups of the Al oxide surface and the water layer formation. Separate calculations confirm small barrier energies for all of the reaction processes.