Functionalization of Ag nanoparticles using local hydrophilic pool segment designed on their particle surface

摘要

The preparation of SiO_2-coated Ag nanoparticles dispersible in various organic solvents has been achieved using a sol-gel reaction of tetraethylorthosilicate (TEOS), in the localized hydrophilic pool segments designed on Ag nanoparticle surfaces. First, oleylamine-capped core Ag nanoparticles were synthesized, followed by ligand exchange with polyethyleneimine (PEI) and further adsorption of an anionic surfactant comprising hydrophilic polyethylene glycol (PEG) chains and hydrophobic alkyl chains, which has previously been reported to improve the stability of nanoparticles in various solvents. Then, a reaction of TEOS with the localized hydrophilic PEI layer on the Ag nanoparticles' surface was conducted by stirring a toluene/TEOS solution of surface-modified Ag nanoparticles at various temperatures. It was found that a SiO_2 layer was successfully formed on Ag nanoparticles when the reaction temperature was increased to 60 °C. It was also found, however, that at this elevated temperature, the primary particle size of Ag nanoparticles increased to several tens of ran, attributable to the dissolution and re-reduction of Ag~+. Because the surface modifier, PEI and anionic surfactant all remained on the nanoparticle surface during the SiO_2 coating process, the prepared SiO_2-coated Ag nanoparticles were found to be dispersible in various organic solvents near to their primary particle size.