APS-silane modification of silica nanoparticles: effect of treatment's variables on the grafting content and colloidal stability of the nanoparticles

Silica nanoparticles, Aerosil 200, with an average primary particle size of 12 nm were chemically modified by gamma-aminopropyltriethoxy silane (APS) via a two-step sol-gel process. Effects of the treatment variables including reaction temperature, water content, and silane concentration on the colloidal stability and the amount of APS grafting on the surface of nanoparticles were studied using thermal gravimetric analysis, diffuse reflectance infrared spectroscopy, and by monitoring the sedimentation behavior of the dispersion of nanoparticles in distilled water as a polar media. Furthermore, the effect of surface modification on the dispersibility of silica nanoparticles in an epoxy novolac coating was evaluated by means of scanning electron microscopy. The results showed chemical interactions between APS and SiO2 nanoparticles. Also, parameters including treatment at ambient temperature, low level of water, and moderate concentration of silane compound, have a considerable effect on the APS grafting content due to the increase of silane hydrolysis and higher silylation coverage of the nanoparticles.