Microemulsification through cavitation
* Presenting author
Abstract:
Acoustic cavitation is very effective to generate microemulsions. The main contributors are the cavitation bubbles that by some means form microemulsions between two immiscible liquids. The flows by which the bubbles create these microemulsions and particularly reduce the size of already existing droplets into smaller droplets is basically unknown. This is partly due to the small size and complex interaction between the bubbles, droplets, and the sound field. To shed light on the fluid mechanics, we study the interaction of a single bubble with a single droplet in an immiscible liquid. We present the dynamics by which microdroplets are generated as a result of the oscillation of a transient cavitation bubble that is created near a water droplet within an oil pool. The initial droplets and the maximum bubble diameter are around 1mm and they are recorded with a high-speed camera. In the experiments the distance of the bubble and the viscosity of the liquid is varied. As a result, we have identified two distinct scenarios by which droplet fragmentation and microemulsification occurs. Additionally, we find that a high oil viscosity leads to the formation of water droplets in oil, while lower viscosities favor external (water-in-oil) and internal (oil-in-water) microemulsification.