Preparation of reactive surface-modified Ag nanoparticles and their assembly on a Si surface via covalent bonds

Surface-modified Ag nanoparticles containing ω-functionalized reactive groups were prepared via the reduction of aqueous AgNO3 in the presence of a modifying agent, O,O'-di(10-undecene) dithiophosphinic acid (UDDPA). The resulting surface-modified Ag nanoparticles were assembled on the surface of hydrogen-terminated Si(111) by a thermal hydrosilylation reaction. The morphologies and structures of the Ag nanoparticles and their assembled film on the Si substrate were characterized by means of transmission electron microscopy (TEM), UV–visible absorption (UV–vis) spectroscopy, Fourier transformation infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). The friction and wear behavior of the assembled film of the surface-modified Ag nanoparticles sliding against GCr15 steel (AISI52100) in a ball-on-plate configuration was evaluated using a UMT-2 friction and wear tester. It was found that the surface-modified Ag nanoparticles had an average diameter of about 10 nm. The surface-modified Ag nanoparticles had unsaturated C = C functional groups sitting at the outermost surface and attached to the Si(111) surface via Si–C bonds. Moreover, the assembled film of the surface-modified Ag nanoparticles showed good friction-reducing ability for sliding against the steel counterpart at a small normal load and sliding velocity, but it had poor antiwear ability and load-carrying capacity and was liable to lose lubricity under severe sliding conditions, owing to a loss of structural integrity and consequent lubrication failure.