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, γ-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 Brönsted type of interaction between nitrogen of DEA and silanol functionality of hydrolyzed GPS.