How Organophosphonic Acid Promotes Silane Deposition onto Aluminum Surface: A Detailed Investigation on Adsorption Mechanism

Many research works have evidenced the importance in using inorganic–organic hybrid materials to protect metal surface or to serve as intermediate adhesion promoter layer for further coating deposition. The main aim of the present work was to elucidate the mechanism of silane deposition onto aluminum surface, in the presence of organophosphonic acid as adhesion promoter and using experimental and theoretical techniques. Transparent thin films of layered inorganic–organic composites were prepared by the sol–gel synthesis of tetraethylorthosilicate and vinyltrimethoxysilane in the presence of 1,2-diaminoethanetetrakis-methylenephosphonic acid. Aluminum surface was characterized by X-ray diffraction, SEM and XPS techniques. On the other hand, inorganic–organic coating was characterized by FTIR and XPS spectroscopies. Density functional theory was employed to evaluate three simplified molecules, orthosilicic acid (Si­(OH)₄), methylphosphonic acid (MePA), and Si­(OH)₃OMePA, by using different coordination modes, in order to approach the most stable chemical bonding between silane-phosphonic groups with modified aluminum surface (i.e., with boehmite as oxidized layer)