Structure of SiO2 gels prepared with different water contents

The influence of the water/alkoxide molar ratio, R-w, on the structure of s ilica prepared by sol-gel with pH = 9 is studied by small-angle neutron sca ttering. A hierarchical microstructure, in which particles are packed in ag gregates that are in turn packed, is found to be a reasonable model for the se xerogels. Porosity exists at different length scales: large light scatte ring pores (>400 Angstrom) between aggregates of particles, small-angle sca ttering pores (<60 Angstrom) between particles and smaller (a few Angstrom) poles within particles. The R-w value affects particle and aggregate sizes and thus porosity. (C) 2000 Elsevier Science B.V. All rights reserved.