Disentangling Origins of Adhesive Bonding at Interfaces between Epoxy/Amine Adhesive and Aluminum

Joining metals by adhesive bonding is essential in widespreadfieldssuch as mobility, dentistry, and electronics. Although adhesive technologyhas grown since the 1920s, the roles of interfacial phenomena in adhesivebonding are still elusive, which hampers the on-demand selection ofsurface treatment and adhesive types. In the present study, we clarifiedhow chemical interactions and mechanical interlocking governed adhesivebonding by evaluating adhesion properties at the interfaces betweenepoxy/amine adhesive and two kinds of Al adherends: a flat aluminumhydroxide (Al (x) O (y) H (z) ) and technical Al plate with roughness.Spectroscopic and microscopical data demonstrate that the protonationof the amino groups in an amine hardener converts Al(OH)(3) on the Al (x) O (y) H (z) surface to AlO(OH). The interfacialprotonation results in an interfacial dipole layer with positive chargeson the adhesive side, whose electrostatic interaction increases theinterfacial fracture energy. The double cantilever beam tests forthe flat Al (x) O (y) H (z) and technical Al substrates clarifythat the mechanical interlocking originating from the surface roughnessfurther increases the fracture energy. This study disentangles theroles of the chemical interactions and mechanical interlocking occurringat the epoxy adhesive/Al interface in the adhesion mechanism.

Automated summary

Adhesive bonding plays a crucial role in various fields like mobility, dentistry, and electronics. However, the understanding of interfacial phenomena in adhesive bonding is still limited, making it difficult to select surface treatment and adhesive types. In this study, the authors investigated the roles of chemical interactions and mechanical interlocking in adhesive bonding between epoxy/amine adhesive and two types of aluminum adherends. They found that protonation of amino groups on the adhesive side resulted in an interfacial dipole layer, which increased the interfacial fracture energy. Furthermore, mechanical interlocking from surface roughness further enhanced the fracture energy. This study provides insights into the adhesion mechanism at the epoxy adhesive/aluminum interface.