Preparation of monosize silica spheres and their crystalline stack

Monosize silica spheres, 0.1 similar to 3 mu m in diameter, were prepared through the hydrolysis and condensation of tetraethylorthosilicate (TEOS) in aqueous ethanol or methanol solutions with ammonia as catalyst. A suspension of the monosize silica, dispersed in EtOH, H2O or a mixture of them, was allowed to sediment, and an ordered, crystalline phase was formed due to an electrostatic repulsion between the silica spheres. Through replacing the H2O or EtOH, in a step wise manner, with another solvent, which is miscible with H2O and EtOH, the Zeta potential on the surface of the silica spheres was reduced, until an ordered closed packed SiO2 material was formed. Because of the monodispersity of the silica spheres, the ordered closed packed SiO2 has a uniform pore size, which can be calculated from the monosize particle's diameter, and can be changed arbitrarily by selecting the size of the monosize silica constructing the SiO2 materials. (C) 1998 Elsevier Science B.V. All rights reserved.