Ultrasound Emulsification in Microreactors: Effects of Channel Material, Surfactant Nature, and Ultrasound Parameters
Shuainan Zhao, Chaoqun Yao, Lixue Liu, Mei Yang, Guangwen Chen
Abstract
Ultrasound emulsification, including the emulsification mechanism as well as the stability and size distribution of the prepared emulsion, was systematically investigated in laboratory-built ultrasonic microreactors. The respective cavitation-induced emulsification processes in hydrophilic and hydrophobic microchannels were first analyzed, after which a bubble shuttling and dispersing mechanism was proposed. The type of prepared emulsion was found to be strongly associated with the hydrophilic–lipophilic balance (HLB) value and water/oil ratio of the emulsified system, but was hardly affected by the ultrasound parameters. The size distribution of the prepared emulsion was characterized using both microscopy and dynamic scattering technique, and was measured to be in the range of 700–1800 nm. It was also found that higher ultrasound intensity, lower frequency, and larger residence time are more favorable to producing fine emulsion. Finally, an operation strategy was proposed on the basis of the experimental results, expecting to provide recommendations for the application of ultrasonic microreactors for continuous emulsification.