Bubble dynamics in complex fluids

The field of bubble dynamics and cavitation, motivated initially by applications in underwater acoustics and later in biomedical ultrasound, continues to evolve. This article describes the recent focus and ongoing developments in understanding and utilizing bubble dynamics in complex fluids. An introductory overview is given of the phenomena of spherical bubble dynamics in complex fluids. The emerging interest in using bubble dynamics to probe high-frequency viscoelastic properties of complex fluids is then highlighted. This interest is motivated by the fact that timescales as short as <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msup> <a:mn>10</a:mn> <a:mrow> <a:mo>−</a:mo> <a:mn>6</a:mn> </a:mrow> </a:msup> <a:mspace width="0.28em"/> <a:mi mathvariant="normal">s</a:mi> </a:mrow> </a:math> can be probed, comparable to the relaxation timescales for complex fluids containing suspended particles or macromolecules. The focus of the article then shifts to specific examples from my research group. First, I present our work on linear rheology of soft solids using ultrasound-driven bubbles. I then discuss how the deformation and flow fields generated by acoustically driven bubbles can modify the microstructure and properties of complex fluids, bearing potential for bubble removal from yield-stress fluids. Finally, I describe our observations of self-assembly of locally ordered microstructures in complex fluids driven by bubble dynamics. In closing, I discuss the growing synergy between the communities of cavitation and rheology, which will be instrumental to address new challenges in the characterization and manipulation of complex fluids.