Acoustic wave propagation in two-phase viscoelastic fluids: The case of polymer emulsions

Wave propagation in two-phase viscoelastic fluid media is studied. A theory based on previous ones for liquid–liquid or liquid–solid mixtures is developed. Acoustical parameters, i.e., velocity of propagation and attenuation, are related to the morphological properties (concentration and size of inclusions) through the thermal and viscoelastic effects. This general theory includes the Newtonian and elastic behaviors as limiting cases. In the case of molten polymer blends, viscoelastic effects may be dominant, unlike most of the Newtonian emulsions studied previously, where thermal effects usually prevail. Moreover, by taking into account the viscoelastic character of the fluids, important changes are obtained not only for the absorption due to the individual components, but also for the excess attenuation in the emulsion.