Emulsification by ultrasound: drop size distribution and stability

The aim of this work is to compare the oil-in-water emulsions produced by mechanical agitation (Ultra-Turrax, 10 000 rpm, P=170 W) or power ultrasound (ultrasound horn, 20 kHz, 130 W) using the same model system : water/kerosene/polyethoxylated (20 EO) sorbitan monostearate. The following parameters were varied : emulsification time, surfactant concentration, consumed power and volume fraction of oil. With ultrasound, the drop size (Sauter diameter, d32) is much smaller than that given by mechanical agitation under the same conditions, which makes insonated emulsions more stable. For a given drop size (d32), less surfactant is required.