Abstract: Monodispersed SiO 2 nanospheres with diameters of 200-800 nm were prepared by improved St?ber method where the tetraethyl silicate ( TEOS ) , deionized water and ethanol were used as the raw materials.To avoid aggregation , the obtained wet nanospheres were dried by vacuum freeze drying technique afterward .The supercritical ethanol was used to modify the surfaces of the SiO 2 nanospheres as hydrophobic .The morphologies and sizes of the nanosphers were investigated by the scanning electron microscope ( SEM ) . And the size distribution of the pores was investigated by N 2 absorption and desorption measurement .The hydrophobic properties of the particles were characterized by measuring their contact angle to water .Fourier transform infrared spectroscopy ( FTIR ) was used to detect the chemical groups on the surfaces of the particles . The results show that the diameter of the SiO 2 nanospheres initially increase and then decrease as the amount of the second addition of TEOS increase . The FTIR results show that by supercritical ethanol treatment , the surface of SiO 2 nanospheres was grafted with alkyl groups successfully , which make the particles show hydrophobic properties .The smallest treated particles show the best hydrophobic performance , with their contact angle to water as high as 149 °.The amount of the treated particles has no obvious influence on the result .With this method , more than 12 g particles could be treated as hydrophobic ( contact angle to water as high as 140°) in one batch , which meet the laboratory-scale demand quite well .Since the hydrophobic SiO 2 nanospheres prepared by us are easy to be dispersed and had the advantage of monodispersity , they would have a potential application in the field of 3-DOM.

Key words: Monodispersed SiO 2 nanospheres with diameters of 200-800 nm were prepared by improved St?ber method where the tetraethyl silicate ( TEOS ) , deionized water and ethanol were used as the raw materials.To avoid aggregation , the obtained wet nanospheres were dried by vacuum freeze drying technique afterward .The supercritical ethanol was used to modify the surfaces of the SiO 2 nanospheres as hydrophobic .The morphologies and sizes of the nanosphers were investigated by the scanning electron microscope ( SEM ) . And the size distribution of the pores was investigated by N 2 absorption and desorption measurement .The hydrophobic properties of the particles were characterized by measuring their contact angle to water .Fourier transform infrared spectroscopy ( FTIR ) was used to detect the chemical groups on the surfaces of the particles . The results show that the diameter of the SiO 2 nanospheres initially increase and then decrease as the amount of the second addition of TEOS increase . The FTIR results show that by supercritical ethanol treatment , the surface of SiO 2 nanospheres was grafted with alkyl groups successfully , which make the particles show hydrophobic properties .The smallest treated particles show the best hydrophobic performance , with their contact angle to water as high as 149 °.The amount of the treated particles has no obvious influence on the result .With this method , more than 12 g particles could be treated as hydrophobic ( contact angle to water as high as 140°) in one batch , which meet the laboratory-scale demand quite well .Since the hydrophobic SiO 2 nanospheres prepared by us are easy to be dispersed and had the advantage of monodispersity , they would have a potential application in the field of 3-DOM.