THE THERMAL-CONDUCTIVITY OF SILICA AEROGEL IN THE PHONON, THE FRACTON AND THE PARTICLE-MODE REGIME

Thermal conductivity data for a homologous series of base-catalyzed silica aerogels confirm that the different length scale regions in the aerogel structure are reflected in the dynamic behaviour, and we determine the contributions from long-wavelength phonons, fractons and particle modes, respectively. In the fracton regime a linear temperature dependence of the thermal conductivity is found as predicted theoretically. Further we observe that the thermal conductivity is proportional to the specific heat in the regime where the thermal properties are dominated by particle modes. From the proportionality constant we deduce a measure of the network connectivity.