Surface modification of silica nanoparticles with hydrophilic polymers

Silica (SiO2) nanoparticles grafted with a water-soluble polymer, i.e. nonionic poly(oxyethylene methacrylate) (POEM) and ionic poly(styrene sulfonic acid) (PSSA) were prepared via a three-step synthetic approach: (1) the activation of silanol group (–OH) in the surface of SiO2 nanoparticles, (2) surface modification to chlorine (–Cl) group and (3) graft polymerization from nanoparticles via atom transfer radical polymerization (ATRP). The successful synthesis and chemical compositions in the modified SiO2 nanoparticles were confirmed using FT-IR, UV–visible spectroscopy and X-ray photoelectron spectroscopy (XPS). Thermogravimetric analysis (TGA) results indicated that the grafting amounts of polymer in the nanoparticles were 5 and 8 wt% for POEM and PSSA, respectively. X-ray diffraction (XRD) showed that the grafting of polymers did not significantly alter the microstructure of SiO2 nanoparticles. Grafting of water-soluble polymer improved the dispersion properties of nanoparticles in alcohol, as verified by scanning electron microscopy (SEM).