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

Abstract

Surface-modified Ag nanoparticles containingω-functionalized reactive groups were prepared via the reduction of aqueousAgNO3 in the presence ofa modifying agent, O,O′-di(10-undecene) dithiophosphinic acid (UDDPA). The resulting surface-modified Agnanoparticles were assembled on the surface of hydrogen-terminated Si(111) by a thermalhydrosilylation reaction. The morphologies and structures of the Ag nanoparticles and theirassembled film on the Si substrate were characterized by means of transmission electronmicroscopy (TEM), UV–visible absorption (UV–vis) spectroscopy, Fourier transformationinfrared (FTIR) spectroscopy, atomic force microscopy (AFM) and x-ray photoelectronspectroscopy (XPS). The friction and wear behavior of the assembled film of thesurface-modified Ag nanoparticles sliding against GCr15 steel (AISI52100) ina ball-on-plate configuration was evaluated using a UMT-2 friction and weartester. It was found that the surface-modified Ag nanoparticles had an averagediameter of about 10 nm. The surface-modified Ag nanoparticles had unsaturatedC = 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 Agnanoparticles showed good friction-reducing ability for sliding against the steelcounterpart at a small normal load and sliding velocity, but it had poor antiwearability and load-carrying capacity and was liable to lose lubricity under severesliding conditions, owing to a loss of structural integrity and consequent lubricationfailure.