STUDY OF THE STOBER REACTION .1. PROPERTIES OF COLLOIDAL SILICA SPHERES PREPARED VIA ALKOXIDE HYDROLYSIS

Monosized spherical colloids were prepared by introducing a constant flow of tetraethoxysilane into a water/ammonia/ethanol mixture of constant composition. It was shown that hydrolysis resulted in nearly completely hydrolyzed silicic acid monomers before polyaddition of the monomer at the surface of the silica seeds contained in the initial reaction mixture. Polymerization resulted in spherical particles which were analyzed at consecutive stages of their formation. The structure of the particles is made of a microporous poly(silicic acid) skeleton, with monomer units of SiO1.83(OH)0.34, with traces of nonhydrolyzed ethoxy groups. Porosity and ethoxy content were shown to depend on the growth rate. Pores are filled with ammonia and water in the reaction mixture. Pores of isolated products could be drained by drying in vacuo and refilled with water in a humid atmosphere.