The sound of small bubbles popping in a droplet*

        Bubble bursting at the air-liquid interface is an important fluid dynamic process responsible for transport of chemical and biological species across through the interface to the atmosphere. The evolution of daughter droplets from these phenomena has significant influence from ocean mass and heat transport to indoor kitchen air quality. Here, we look at the physics of bubble bursting by placing a droplet of liquid on a superhydrophobic surface (SH), then adding an air bubble and watching it pop. An acoustic microphone and piezoelectric contact microphone system are synchronized with a high speed camera to unravel the physical behavior of the bubble bursting. We observed that the emanating jet length strongly depends on the surface tension of the liquid and bubble size for a fixed droplet volume.  The frequency of the bubble bursting induced capillary wave decreases with decreased surface tension.  At saturated surfactant concentrations (8.1 mM sodium dodecyl sulfate), the capillary wave also propagates slowly, resulting in lower pressure forces. In addition, with increase in bubble size, the frequency of the capillary waves increases for a given volume and type of droplet liquid.