Adsorption and stability of self-assembled organophosphonic acid monolayers on plasma modified Zn-Mg-Al alloy surfaces

The adsorption and stability of adhesion promoting organophosphonic acid monolayers on plasma modified Zn-Mg-Al alloy surfaces were investigated by means of microscopic and spectroscopic techniques. A strip hollow cathode (SHC) was chosen for the plasma surface modification. The chemical composition of the plasma treated surfaces and the influence of reducing and oxidizing plasma modifications on the corrosion properties of Zn-Mg-Al alloy surfaces were analyzed by means of X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry, respectively. The adsorption and stability of phosphonic acid monolayers were comparatively studied on plasma modified and non-plasma modified Zn-Mg-Al alloy surfaces. Self-organization of monofunctional monolayers was confirmed by means of polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS) and XPS. Contact angle measurements were performed to prove the stability of the octadecylphosphonic acid (ODPA) monolayer on the native and different plasma treated surfaces in aqueous media. Plasma modification and ODPA adsorption resulted in a synergistic inhibition of the redox current densities of the alloy surface. The strongest inhibition was observed for an Ar/H-2 plasma + O-2 plasma treatment followed by octadecylphosphonic acid self-assembled monolayer adsorption. (C) 2013 Elsevier B.V. All rights reserved.