Bubble dynamics in complex fluids

Bubble dynamics and cavitation have traditionally been studied in the context of underwater acoustics and, more recently, biomedical applications. I will discuss how the deformation and flow fields generated by acoustically-driven bubbles can be used to drive self-assembly of novel microstructures in complex fluids. Bubble dynamics driven at ultrasonic frequencies probe time scales as short as $10^{–3} - 10^{–6}$ s, comparable to the smallest relaxation time scales for complex fluids containing suspended particles or macromolecules. I will describe how, in this dynamical regime, dynamic capillary interactions arise between colloidal particles adsorbed at a fluid interface, producing particle networks that dominate the mechanics of these complex interfaces under flow. I will also describe a new flow-induced mechanism caused by bubble dynamics, that produces ordered microstructures in colloidal gels. This mechanism can enable energy-efficient processing methods of colloidal-gel materials, including inks, battery electrodes, construction materials. I will also discuss the emerging approach of using bubble dynamics to probe the high-frequency viscoelastic properties of complex fluids and soft materials, which has brought together the communities of cavitation and rheology to address new challenges in characterization of soft materials.