Effect of temperature on the ultrasonic properties of oil-in-water emulsions

The influence of temperature on the ultrasonic properties of oil-in-water emulsions was investigated. The ultrasonic velocity and attenuation coefficient of a series of corn oil-in-water emulsions with different disperse phase volume fractions (phi=0 to 0.5) and mean droplet radii (r =0.1 to 0.5 mu m) were measured as a function of temperature (5 to 50 degrees C). These measurements were in reasonable agreement with predictions made using ultrasonic scattering theory. The ultrasonic velocity of the emulsions was particularly sensitive to their composition, temperature and droplet size. Around 15 degrees C, the ultrasonic velocity was fairly insensitive to oil concentration. Below this temperature, it increased with oil concentration, whilst above this temperature it decreased. The ultrasonic velocity increased with droplet size. The attenuation coefficient of the emulsions was much more sensitive to composition and droplet size, rather than temperature. It increased with oil concentration and decreased with temperature. The implications of these results for the use of ultrasound for determining the size distribution and concentration of droplets in emulsions are investigated. (C) 1998 Elsevier Science B.V. All rights reserved.