It has been reported in the literature that the composition Unsupported silica membranes were prepared by acid-catalyzed of the synthesis solution influences the structure of the spehydrolysis and condensation of tetraethylorthosilicate. The possicies in the sol (3) and, hence, the final structure of the bility of tailoring the pore size and porosity of microporous silica membrane. This possibility to tailor-make membranes can membranes was investigated by varying the amounts of reactants. be of advantage in manufacturing application-oriented mem-A wide range of porosities of 0 to 30% could be obtained. Of the branes with different porosity or pore size. To prepare memvaried parameters, the acid concentration in the reaction mixture branes with predefined properties, it is important to underis of most importance for the variation in porosity. The pore size stand the relationship between the synthesis conditions and distribution was calculated from nitrogen adsorption isotherms, the resulting structure of the membranes. The first step in by using the Horva ´th-Kawazoe method. This resulted in an average pore diameter of 5 A ˚with a broad tail up to 10 A ˚. ᭧ 1996 this investigation was to study the relationship between the Academic Press, Inc.