SELF-ASSEMBLED MONOLAYERS OF LONG-CHAIN HYDROXAMIC ACIDS ON THE NATIVE OXIDES OF METALS

Long-chain alkanehydroxamic acids adsorb on the native oxides of metals and formed oriented self-assembled monolayers (SAMs). This study examined SAMs of hydroxamic acids on the native oxides of copper, silver, titanium, aluminum, zirconium, and iron. These SAMs were characterized using wettability, X-ray photoelectron spectroscopy (XPS), and polarized infrared external reflectance spectroscopy (PIERS). Alkanehydroxamic acids give better monolayers than the corresponding alkanecarboxylic acids on certain basic metal oxides (especially copper(II) oxide). On the native oxide of copper (which has an isoelectric point greater than the pK(a) of the hydroxamic acid), the ligand is bound to the surface predominantly as the hydroxamate. The strength of the interaction between copper oxide and the hydroxamate allows incorporation of polar tail groups into the monolayer. On acidic or neutral metal oxides (e.g., TiO2), the predominant species bound to the surface is the hydroxamic acid. Alkanehydroxamic acids on titanium dioxide bind relatively weakly but, nonetheless, form SAMs that are more stable than those from carboxylic acids (although not as stable as those from alkanephosphonic acids).