Synthesis of Monodisperse Silica Nanoparticles Dispersable in Non-Polar Solvents

Three synthetic routes to hydrophobic silica nano particles are compared in this paper. First, the established synthetic method based on the Stober process was examined. Monodisperse colloidal silica particles with diameters of 15-25 nm were prepared via the hydrolysis of tetraethyl orthosilicate (TEOS) by aqueous ammonia in ethanol. The surfaces of these particles were rendered hydrophobic with octadecyltrimethoxysilane (ODTMS) after the reaction or, more conveniently, during the growth phase. Secondly, silica particles with diameters of 15-50 nm were prepared using a one-pot synthesis in which TEOS was hydrolyzed by an amino acid and the resulting particles were coated with ODTMS. Lastly a novel, direct approach to the synthesis of hydrophobic organosilica nanoparticles was developed using ODTMS as the single silica source. Hydrolysis of the ODTMS by aqueous ammonia in ethanol yielded monodisperse colloidal organosilica particles with diameters of 15-30 nm.