Small-angle neutron scattering from silica aerogels reveals that they form mutually self-similar volume fractals for a wide range of densities and preparations. The fractal dimension is D=2.40±0.03. The fractal behavior extends down to near-molecular sizes. Indication for a volume-to-surface fractal crossover is also obtained. These results apply to neutrally prepared or acid-catalyzed materials. Base-catalyzed gels have widely different properties.

• Received 15 October 1987

DOI:https://doi.org/10.1103/PhysRevB.37.6500