Characterization of Organofunctional Silane Films on Zinc Substrates

Organofunctional silane films formed on pure zinc substrates from aqueous solutions were characterized by ellipsometry, contact angle measurements, reflection absorption infrared spectroscopy (RAIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The silanes studied were gamma-aminopropyltriethoxysilane (gamma-APS) and gamma-ureidopropyltrialkoxysilane (gamma-UPS). The deposition parameters included solution concentration, solution dipping time, and pH value of the applied solution. Effects of these deposition variables on the thickness of the film, the surface energy of the film, the chemical structure of the film, and the surface topography of the film are discussed. The effect of film aging time on the surface energy of silane-coated pure zinc substrates was also studied. It was found that the silane film thickness obtained depends primarily on the applied solution concentration and is independent of the solution dipping time. The molecular orientations of the applied silane film are determined by the pH value of the applied silane solution and the isoelectric point of the metal substrates. The deposition window in terms of pH value for zinc substrates was between 6 and 9. The total surface energy of silane-coated pure zinc substrate decreases steeply with film aging time for gamma-APS but not for gamma-UPS. The stability of both silane films improved after aging in the air.