Frequency-dependent compressibility in emulsions: Probing interfaces using Isakovich's sound absorption

¹ Hannah Research Institute, Ayr, Scotland UK KA6 5HL
² Laboratoire de Dynamique des Fluides Complexes, Institut Le Bel, 4 rue Blaise Pascal, 67070 Strasbourg, France
³ Ecole Normale Supérieure de Lyon, Laboratoire de Physique, 46 Allée d'Italie, 69364 Lyon Cedex 7, France

Received: 31 October 1997
Accepted: 13 March 1998

Abstract

The average compressibility of an emulsion acquires a frequency-dependent, relaxing behavior due to the thermoconduction between adjacent phases heated through thermo-mechanical coupling. Introducing the relaxing compressibility into the sound propagation equations, we extend Isakovitch's theory of sound absorption to emulsions of an arbitrary number of liquids with the same density. The sound propagation speed and attenuation are found to be isotropic, even if the emulsion morphology is anisotropic. In the limit of frequencies greater than the inverse heat diffusion time, both the relaxing part of the compressibility and the sound attenuation are proportional to a single parameter depending linearly on the emulsion interfacial area per unit volume, thus giving easy access to this quantity in non-transparent systems.