EFFECT OF TEMPERATURE ON THE ULTRASONIC PROPERTIES OF OIL-IN-WATER EMULSIONS

The influence of temperature on the ultrasonic properties of oil-in-wa ter emulsions was investigated. The ultrasonic velocity and attenuatio n coefficient of a series of corn oil-in-water emulsions with differen t disperse phase volume fractions (phi=0 to 0.5) and mean droplet radi i (r =0.1 to 0.5 mu m) were measured as a function of temperature (5 t o 50 degrees C). These measurements were in reasonable agreement with predictions made using ultrasonic scattering theory. The ultrasonic ve locity of the emulsions was particularly sensitive to their compositio n, temperature and droplet size. Around 15 degrees C, the ultrasonic v elocity was fairly insensitive to oil concentration. Below this temper ature, it increased with oil concentration, whilst above this temperat ure 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 implicatio ns of these results for the use of ultrasound for determining the size distribution and concentration of droplets in emulsions are investiga ted. (C) 1998 Elsevier Science B.V. All rights reserved.