Two fractal structures in aerogel

Abstract Composite aerogels have been prepared by the addition of silica soot (aerosil) in the solution before gelation. The fractal network previously described which results from the aggregation mechanism of the organosiloxane is strongly affected by the influence of the aerosil soot. Ultra small angle X-ray scattering measurements at ESRF show that besides the fractal network built up by the organosiloxane, the silica soot is forming another fractal structure at a higher scale. The fractal dimension characterizing the inorganic network could be interpreted as the signature of the linkage between the polymeric clusters. From a mechanical point of view, for aerosil content lower than 40 wt% , the elastic modulus is not dependent on the aerosil fractal network and the mechanical features are those of the polymeric gel.