Fabrication of composite particles by attaching surface-modified nanoparticles to core particles by wet processing in organic solvents

A simple wet processing route for the formation of composite particles via the adsorption of highly dispersible nanoparticles onto the core particles in organic solvents, without the formation of strong aggregates, was developed. The process involved a simple mixing procedure using core particles and surface-modified highly dispersible nanoparticles (shell nanoparticles) in organic solvents, assisted by ultrasonication. As a model study, submicron-sized (ca. 400 nm) and nano-sized (ca. 30 nm) SiO2 particles, prepared by Stِber process, were applied as the core and shell materials, respectively. The surface of the shell SiO2 nanoparticles was modified by a layer-by-layer process that involves the adsorption of cationic polyethyleneimine and an anionic surfactant comprising branched alkyl and polyethylene glycol chains for improving the stability in various organic solvents, as well as for controlling the interaction with the core material. The surface modified shell SiO2 nanoparticles were found to be effectively adsorbed onto the core SiO2 particles when mixed in toluene, while minimal adsorption was observed in ethanol. The obtained composite particles showed improved stability compared to raw core SiO2 particles in toluene. The adsorption mechanism of the shell SiO2 nanoparticles on the core particles in various organic solvents was proposed on the basis of surface-interaction measurements by atomic force microscopy colloidal probe methods. We believe that a long-range adhesive force between the shell SiO2 nanoparticles and the core particles played an important role in promoting effective adsorption, allowing the formation of composite particles.