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

Abstract

Joining metals by adhesive bonding is essential in widespread fields such as mobility, dentistry, and electronics. Although adhesive technology has grown since the 1920s, the roles of interfacial phenomena in adhesive bonding are still elusive, which hampers the on-demand selection of surface treatment and adhesive types. In the present study, we clarified how chemical interactions and mechanical interlocking governed adhesive bonding by evaluating adhesion properties at the interfaces between epoxy/amine adhesive and two kinds of Al adherends: a flat aluminum hydroxide (Al x O y H z ) and technical Al plate with roughness. Spectroscopic and microscopical data demonstrate that the protonation of the amino groups in an amine hardener converts Al­(OH)3 on the Al x O y H z surface to AlO­(OH). The interfacial protonation results in an interfacial dipole layer with positive charges on the adhesive side, whose electrostatic interaction increases the interfacial fracture energy. The double cantilever beam tests for the flat Al x O y H z and technical Al substrates clarify that the mechanical interlocking originating from the surface roughness further increases the fracture energy. This study disentangles the roles of the chemical interactions and mechanical interlocking occurring at the epoxy adhesive/Al interface in the adhesion mechanism.

Simulation Study of the Effect of Nanoporous Surfaces on the Adhesion Properties of Cross-Linked Polymer Networks

“…It is worth noting that when a rough surface is prepared by chemical treatment, the generated surface roughness does not necessarily include only vertical holes. Actually, complicated sponge-like structures in the scale of 100–200 nm were observed at the treated epoxy resin and Al interfaces by scanning transmission electron microscopy, in which the polymer resin can easily be hooked by forming loops. Moreover, existence of nanopores leads to large shear strength, as reported by our previous simulation study .…”

“…Recently, we have investigated the adhesion properties between epoxy resins and aluminum (Al) substrates . Our experiments by the double-cantilever beam revealed that the mechanical interlocking enhanced adhesion strength by 39 times compared to flat Al samples.…”

Molecular Understanding of the Distinction between Adhesive Failure and Cohesive Failure in Adhesive Bonds with Epoxy Resin Adhesives

“…This suggests that the threshold value at which the failure mode of the epoxy adhesive changes from adhesive failure to cohesive failure is close to 3 OH/nm 2 . Given that both simulations and interface fracture toughness measurements for the adhesive interface between the epoxy-amine adhesive and the aluminum surface conducted by Horiuchi and co-workers suggest an estimated interaction point density of 0.16 points/nm 2 , the hydroxyl group density of 3–4 OH/nm 2 reported by Tomasovic et al may be said to be high. However, not all functional groups contribute to adhesion interactions.…”

Multifunctional Acrylic Polymers with Enhanced Adhesive Property Serving as Excellent Edge Encapsulant for Stable Optoelectronic Devices

“…As an omnipresent tool, adhesives are used not only in daily life but also in a variety of industries, including construction, healthcare, optoelectronics, and transportation. − Especially in the automotive industry, adhesives are gaining attraction due to the global demand to replace glass windows with transparent plastics. − Among transparent plastics, polycarbonate (PC) has the advantage of being lightweight, impact-resistant, and facilely processable. , However, its poor weathering, abrasion, and scratch resistances have hindered its commercialization. , Therefore, the hard-coating method has been researched to compensate for the shortcomings of the PC surface. − However, the inherently low adhesive properties between substrates composed of organic polymers and hardcoats, hereinafter referred to as topcoats containing inorganic components can be problematic. , Consequently, it is necessary to introduce an adhesive layer (AL) at the interface to overcome the delamination issue while maintaining the surface mechanical properties of the topcoat. Furthermore, adhesives can also be applied in the optoelectronics field to encapsulate optoelectronic devices based on perovskites or organic materials that are vulnerable to ambient air and humidity. − Perovskite solar cells (PSCs) have advanced from a power conversion efficiency of 0.8% in 2009 to over 25.5% in 2020. , However, the inherent instability of the halide perovskites in ambient air has been a barrier to commercialization. , Hence, encapsulation methods such as glass cover encapsulation have been studied as a measure against the impact of air. , Furthermore, encapsulation with an adhesive edge sealant is the most cost-effective method, as it allows for moisture protection with minimal sealant. − Among all the adhesives for the applications of ALs and edge sealants, polymeric adhesives are suitable for achieving high thermal durability, transparency, and strong adhesion. − …”