The interaction of a commercial dry film adhesive with aluminium and organosilane treated aluminium surfaces: a study by XPS and ToF-SIMS

XPS and ToF-SIMS have been employed to study the interaction of solutions of a commercial dry film adhesive with grit-blasted aluminium and grit-blasted aluminium coated with an organosilane adhesion promoter, γ-glycidoxypropyltrimethoxy silane (GPS). From adsorption isotherm studies derived from XPS and ToF-SIMS results, it is shown that the adhesive uptake on both substrates was by chemisorption. The isotherm curves from XPS data indicated that the adhesive uptake on both substrates was similar. The uptake curves plotted using the relative peak intensity of ToF-SIMS characteristic fragment at m/z=58+ against the adhesive concentrations showed an important result. This fragment is characteristic of the curing agent as a result of chain scission of the end of the curing agent molecule. The adsorption isotherm demonstrated that the intensity for the grit-blasted surface was greater (by a factor of two) than that for a GPS coated surface. This is because on the bare surface, both ends of the molecule were available to yield the m/z=58 fragment, whereas on the GPS coated surface one end was immobilised by the interaction with the glycidoxy functionality. MS spectra exhibit a characteristic feature at m/z=277+ for both substrates. The presence of this ion is important evidence of a specific interaction occurring on both substrates. It was found that it is indicative of the formation of a covalent bond. On the surface not primarily treated with silane primer, the covalent bond is formed by partial crosslinking within the adhesive. On the surfaces treated with GPS and then the adhesive, this bond is from the interaction between the curing agent and either the epoxy functionality from the adhesive or the GPS.