Structure and dynamics of silica aerogels

The current status of our experiments on fractal silica aerogels is reviewed. Remarks are made concerning the direct space observations of the structure compared with reciprocal space measurements. The scaling of the intensities observed in the Raman scattering from fractons is analysed in the light of recent theoretical progess. The origin of, and evidence for, an elasticity cross-over in the fracton frequency range are discussed. The fracton dimension d is clearly shown to be an additional dimension to characterize the fractal rather than a universal quantity. © 1992 Taylor & Francis Ltd.