Experimental investigation of microstreaming induced by free nonspherically oscillating microbubbles

Microbubbles exposed to a sufficiently strong ultrasound field can show nonspherical oscillations called surface modes. In the vicinity of the bubble surface, these oscillations induce a slow mean flow named microstreaming. Microstreaming plays an important role in medical applications such as sonoporation as well as in engineering applications such as micromixing. A better understanding of the induced flows will hence be beneficial to a large number of applications. Recent studies mainly report on microstreaming induced by bubbles resting on a solid boundary. The observation of microstreaming around a single, free bubble is challenging, because several experimental difficulties have to be overcome: Avoidance of translational instabilities, obtainment of a steady-state behavior maintaining surface modes, correct choice of tracer particles, and correlation between fast temporal bubble dynamics and relatively slow microstreaming. We present an experimental setup, that accomplishes the simultaneous visualiza...