Ultrasonic imaging of gravitational separation in emulsions

An ultrasonic imaging technique was developed to monitor gravitational separation in emulsions. A series of 20 wt.% corn oil-in-water emulsions (d(32) = 1.32 mu m), stabilized by a non-ionic surfactant, were prepared with different concentrations of xanthan in the aqueous phase (0-0.08 wt.%). Gravitational separation in these emulsions was then measured at 0 and 24 h using ultrasonic imaging. Data is presented in the form of two-dimensional images of the extent of creaming or as the variation of droplet concentration with emulsion height. Creaming was slow at low (<0.0075 wt.%) and high (>0.02 wt.%) xanthan concentrations, but rapid at intermediate concentrations, because of the influence of xanthan on colloidal interactions and the rheology of the continuous phase. Additional measurements using ultrasonic spectrometry indicated that the droplets in emulsions containing high xanthan concentrations were flocculated, even though they did not cream. This study demonstrates that ultrasonic imaging is a powerful technique for non-destructive monitoring of creaming in concentrated emulsions. (C) 1998 Elsevier Science B.V.