Interaction of epoxy analogue molecules with organosilane-treated aluminum: A study by XPS and ToF-SIMS

Specimens treated with solutions of an epoxy analogue molecule, diethanolamine (DEA), have been studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The initial substrates were of two different types: grit-blasted aluminum and aluminum coated with an organosilane adhesion promoter, gamma-glycidoxy propyl trimethoxy silane (GPS). Specific interactions between the aluminum substrate and/or GPS treated aluminum and DEA are proposed on the basis of XPS and SIMS data. On oxidized aluminum. DEA forms either a single alkoxy or two alkoxy bonds (bridge). The formation of the so-called bridge brings the nitrogen atom close to the substrate. The nitrogen atom of DEA interacts with the surface via formation of a hydrogen bond or via donor-acceptor interaction with an aluminum atom. When deposited onto GPS-coated aluminum, DEA undergoes two types of interactions: formation of covalent bond with nucleophilic addition or Bronsted type of interaction between nitrogen of DEA and silanol functionality of hydrolyzed CPS.