High density silanization of nano-silica particles using γ-aminopropyltriethoxysilane (APTES)

A novel and efficient process was developed for high density silanization of nano-silica particles using APTES, in which 13.48 APTES nm−2 was achieved. This process comprises three stages, namely, aqueous mixing, spray drying and thermal treatment. After the successive stages, the APTES conversions were 25.3%, 50.7% and 80.6%. In the aqueous mixing stage, the chemical reaction was fast and quite limited. In the spray drying stage, APTES was distributed on the surface of nano-silica particles uniformly by both physical and chemical adsorption. In the thermal treatment stage, the processing temperature (T) and time in the thermal treatment had large effects on the grafting density, and the reaction was reversible. When T < 300 °C, the reverse reaction dominated, causing a decrease of APTES grafting density. When T > 300 °C, the forward reaction dominated, leading to increased grafting density. The optimum processing temperature and time for high grafting density were 360 °C and 30 min, respectively.