Revision of the mechanisms behind oil-water (O/W) emulsion preparation by ultrasound and cavitation.

Today emulsion preparation is receiving a lot of scientific attention, since emulsions are playing an essential role in many of the big industries, such as food, pharmaceutical or cosmetic industry. One of the most promising techniques for emulsion preparation is ultrasound emulsification. The purpose of this study is to expand the knowledge on the ultrasonically assisted emulsification model, that has not been amended since 1978. The model explains that oil-in-water emulsion formation is a two-step process. Firstly, the surface of the oil phase is disturbed and separated by the acoustic waves. Secondly, cavitation implosions further disrupt and disperse oil drops. We have used a high-speed camera to closely observe oil-in-water emulsion formation. The images show, that the ultrasound emulsification process is profoundly more complex. While the first and the last step of emulsion formation are the same as believed until now, additional intermediate stages of water-in-oil and even oil-in-water-in-oil occur.