Interaction of anhydride and carboxylic acid compounds with aluminum oxide surfaces studied using infrared reflection absorption spectroscopy

The chemical bonding of three different anhydride and carboxylic acid based compounds with a set of differently prepared aluminum substrates has been investigated using infrared reflection absorption spectroscopy. The compounds were selected to model typically used adhesives, coatings, and self-assembling monolayers. The purpose of the investigation was to study the interaction of these functional groups with the aluminum oxide surface and to determine whether this interaction is influenced by the changes in chemistry and composition of the oxide layer. The extent to which the compounds resisted disbondment in water was also investigated. The oxide layers on the differently prepared substrates were all found to be capable of hydrolysis of the anhydride group, resulting in the formation of two carboxylic acid groups. Subsequently, both of the carboxylic acid groups became deprotonated, to form a coordinatively bonded carboxylate species. The same behavior was also observed for monofunctional carboxylic acids. For all different oxides layers, the carboxylate was found to be coordinated in a bridging bidentate way to two aluminum cations in the oxide layer. The oxide layers showed however clear differences in the amount of molecules being chemisorbed. A relation was established with the amount of hydroxyls present on their surfaces, as determined from X-ray photoelectron spectroscopy measurements. The coordinative bonding of a monofunctional carboxylic acid group to the oxide surface was found to be not stable in the presence of water, while a bifunctional carboxylic acid group could resist displacement by water for a prolonged period of time.