Collapse dynamics of bubble pairs in gelatinous fluids

Bubble dynamics is relevant in a variety of research fields that range from material science to medical applications. It is studied extensively, and researchers apply very established and reliable experimental methods. Although these methods provide many advantages and are constantly modified and adapted, there are also some limitations on which aspects can be analyzed. Thus, we present in this study a novel experimental setup that uses a shock tube and applies a gelatinous mixture as a water-like carrier medium. Millimeter-sized air bubbles, placed in the gelatin and exposed to an instantaneous pressure increase, are analyzed under two different aspects. First, we show that single bubbles in the gelatin behave very similarly to bubbles in water during the collapse and that different gelatin concentrations do not significantly affect the behavior. In a second part, we study interacting bubble pairs and differentiate four main types of interaction that can also be characterized by non-dimensional parameters. A well-known type, jetting towards each other, is reproduced and a type termed `reversing collapse' shows similarities to previous work as well as new aspects. The interaction of bubbles of large size ratios is either dominated by the large bubble if bubbles are far apart or leads to a pronounced liquid jet if the bubbles are close to each other. The presented results demonstrate that the applied experimental setup can provide insight into bubble interaction and jet formation. This could help, for example, to establish controlled and directed jetting of microbubbles in targeted drug delivery, which would play a major role in anticancer research.