Covalent attachment of polymer thin layers to self-assembled monolayers on gold surface by graft polymerization

Graft polymerization of functional monomers onto self-assembled monolayers (SAMs) on gold via argon plasma treatment and then UV irradiation has been carried out. Two alkanethiols, viz., 3-mercaptopropionic acid and 3-mercaptopropionic acid-2-ethylhexyl ester, were employed for the deposition of SAMs from ethanol solutions onto gold surfaces. The monomers used for graft polymerization were water-soluble acrylic acid (AAc) and hydrophobic allylpentafluorobenzene. Angle-resolved X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to investigate the surface chemical composition, surface coverage, film thickness, and wettablity. XPS results suggest that mild and brief plasma treatments can be employed to generate sufficient peroxides and hydroperoxides on the SAMs for the subsequent UV-induced graft polymerization while maintaining the SAMs intact. For all the cases investigated, XPS results reveal that the graft polymer forms a thin layer of 6-7 nm in thickness on the SAM surfaces. Contact angle measurements indicate that the SAM-modified Au surfaces could be selectively made hydrophilic or hydrophobic through the graft copolymerization with an appropriate monomer. It was also demonstrated that the AAc graft polymerized SAMs selectively adsorbed Fe3+ ions via coordination complexation. (C) 2002 Elsevier Science B.V. All rights reserved.