Structure and stability of adhesion promoting aminopropyl phosphonate layers at polymer/aluminium oxide interfaces

Aminopropylphosphonic acid was investigated as a short-chain bi-functional adhesion promoter between an aluminium alloy and an epoxy amine adhesive. Benefits of the short-chain adhesion promoter are its high solubility in water and epoxy resins, and the formation of densely packed monolayers on the aluminium substrate during the adsorption from both media. Application of the adhesion promoter as an adhesion promoting monolayer adsorbed from aqueous solution and as an additive to the adhesive bulk was investigated. By means of XPS and SAM analysis, monolayer formation on the aluminium passive layer and, at lower coverage, on intermetallic particles was demonstrated. Formation of ionic bonds to the aluminium oxihydroxide surface via acid/base interactions in bi-dentate conformation was proven by means of FTIR-RAS. Filiform corrosion tests, utilized as probe for interfacial stabilization, showed a strong inhibition of this anodic de-adhesion process for both variations of application.