Effect of Interfacial Energetics on the Protection of Steel and Aluminum Surfaces by Alkyl Acid Coatings

Abstract

The temperature-dependent endurance of alkyl phosphate acid, alkylsulfonic acid, and hydroxamic acid coatings on steel and aluminum surfaces is explored. The coatings are applied to the metal surface and then challenged with polymeric methylenebis(phenyl isocyanate) (pMDI), an aggressive reagent with affinity for metal surfaces. The progress of the chemical attack on the coating is observed by measurement of contact angles as a function of temperature, and the chemical result of the attack is confirmed by X-ray photoelectron spectroscopy. The data show that the coating performance is dependent on the interaction energy of the headgroup with the metal oxide layer consistent with studies of self-assembling monolayers. Additionally, the importance of specific interactions between the pMDI and the oxide surface can result in nonlinear wetting behavior.