Transformation of nanostructure of silica gels during drying

Small angle X-ray scattering (SAXS) experiments performed on silica gels dried by different methods show that for some of them, intensity oscillations occur around the Porod law. These oscillations have been analysed to give a chord length distribution of the solid network of the gels. Primary solid particles are rough in xerogels and CO2 evacuated aerogels. Aerogels obtained by methanol supercritical drying show a smooth surface with a well definited chord length distribution curve. These features are explained by silica dissolution-redeposition reactions occurring during the supercritical drying treatment in methanol. (C) 2000 Elsevier Science B.V. All rights reserved.