[SY-O5] Unveiling the chemical reactions involved in moisture-induced weakening of adhesion between aluminum and epoxy resin: a hybrid quantum-classical simulation study
Epoxy resin is commonly used as an adhesive for bonding metals. Recent industrial demands, e.g., light-weight multi-material cars and highly reliable pressure sensors, motivate researchers to improve the reliability and durability of bonded materials. One critical issue regarding adhesive bonding is the weakening of its bonding strength by the water that migrates from a moist environment along the interface. When bonding naturally surface-oxidized aluminum with epoxy resin, the adhesion strength reduces by about 40 % in a moist environment. Surface treatment techniques, such as sealing with polyvinyl chloride, only delay such adhesion weakening.
Despite the importance of this issue, adhesion weakening is not well understood. 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 1,500 atoms at the contact region are treated with density-functional theory.
For the first time, calculated adhesion strengths compare well with the experimental values. Former simulations gave one order of magnitude larger adhesion strength than the experimental value. Three types of chemical reactions that affect the adhesion strength are found to 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 the reaction processes.
Despite the importance of this issue, adhesion weakening is not well understood. 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 1,500 atoms at the contact region are treated with density-functional theory.
For the first time, calculated adhesion strengths compare well with the experimental values. Former simulations gave one order of magnitude larger adhesion strength than the experimental value. Three types of chemical reactions that affect the adhesion strength are found to 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 the reaction processes.