Abstract
The interfacial chemistry of a polysulphide sealant, adhesive components, and a commercial adhesive, on aluminium and aluminium treated with an organosilane adhesion promoter has been investigated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of a pre-bonding hydration procedure has been investigated as a function of process parameters. The adsorption of the same organic species on these porous surfaces has also been studied. A novel approach has been developed to study the degradation of interfacial chemistry by water. In the study of the adsorption of the sealant, it was found that the liquid polysulphide component was in competition with other, unknown, components contained in the commercial formulation, leading to a low level of adsorption of the polysulphide component. With the GPS treatment, the uptake of the polysulphide component increased. In the study of the adsorption of pre-polymer and curing agent adhesive components, commercial adhesive, and a mixture of the two major components on non-hydrated surfaces, it was found that the adsorption was of the Langmuir type and donor-acceptor interactions were observed. For the commercial adhesive, a specific interaction was observed at the adhesive/silane interface, demonstrated by the presence of an ion at m/z = 277 Da. This resulted from the formation of a covalent bond between the organosilane and the curing agent. The same types of interfacial interactions were also observed on hydrated surfaces, but in the study of the adsorption of the adhesive prepolymer alone and the commercial adhesive on hydrated surfaces, it was found that the adsorption behaviour was of BET Type IV form, rather than simple monolayer adsorption. The chemical bonding at the adhesive/silane/aluminium interface and the adhesive/aluminium interface was challenged by exposure to water. The degradation of the interfacial chemistry of the adhesive occurred rapidly even when a silane treatment was employed. This indicated that although the covalent bond was responsible for good durability, in the absence of the ‘bulk’ adhesive, it is susceptible to rapid hydrodynamic attack.