Optical Observation of Microcapsule Destruction in an Acoustic Standing Wave

Abstract

The destruction of microcapsules having an elastic thin shell is discussed. An optical observation of the capsule destruction using a high-speed video camera is carried out. As the driving pressure is increased, the microcapsules trapped at the antinode of an acoustic standing wave show circling movements, and then the microcapsules eventually collapse. At the moment of destruction, it is found that the microcapsules change in shape and the internal gas jets out of the capsule rapidly. The sound pressure threshold for the capsule destruction is the lowest under the resonant condition. The capsule destruction also depends on the existence of free bubbles in the surrounding media. It is found that the mechanism of capsule destruction can be categorized into two types: one is due to the increasing driving sound pressure and the other is due to the existence of the free bubbles in the surrounding media. It is considered that the destructions of multicapsules depend on some parameters; however, these two types of capsule destruction are dominant factors.