Ultrasonic propagation in highly concentrated oil-in-water emulsions

The dependence of the ultrasonic attenuation spectra (0.4-160 MHz) of n-hex adecane oil-in-water emulsions on droplet concentration (1-92 vol %) was me asured. In dilute emulsions the attenuation coefficient increased with drop let concentration, but in concentrated emulsions it decreased. Traditional multiple scattering theory (Allegra and Hawley-Waterman and Truell) greatly overestimated the attenuation, even at moderate concentrations (>10%), bec ause it ignores thermal overlap effects. On the other hand, an extended mul tiple scattering theory that takes these effects into account gives good ag reement with experimental measurements up to much higher droplet concentrat ions (50-70%). Neither theory could be used to accurately predict the ultra sonic properties of highly concentrated emulsions (>90%).