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

Long-chain alkanehydroxamic acids adsorb on the native oxides of metal s and formed oriented self-assembled monolayers (SAMs). This study exa mined SAMs of hydroxamic acids on the native oxides of copper, silver, titanium, aluminum, zirconium, and iron. These SAMs were characterize d using wettability, X-ray photoelectron spectroscopy (XPS), and polar ized infrared external reflectance spectroscopy (PIERS). Alkanehydroxa mic acids give better monolayers than the corresponding alkanecarboxyl ic 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 sur face predominantly as the hydroxamate. The strength of the interaction between copper oxide and the hydroxamate allows incorporation of pola r tail groups into the monolayer. On acidic or neutral metal oxides (e .g., TiO2), the predominant species bound to the surface is the hydrox amic acid. Alkanehydroxamic acids on titanium dioxide bind relatively weakly but, nonetheless, form SAMs that are more stable than those fro m carboxylic acids (although not as stable as those from alkanephospho nic acids).