Buoyancy-Marangoni Fingering of a Miscible Spreading Drop

We experimentally investigate the interfacial instability that emerges when a water droplet is deposited on a bath of glycerol-water solution. Despite the absence of surface tension to stabilize short-wavelength undulations, we observe finite-size fingers that grow and pinch off from the drop. We show that the fingering patterns formed in the experiments resultes from a balance between the outward buoyancy effect and inward Marangoni flow. This induced Marangoni flow inhibits small perturbations and acts as an effective surface tension on the miscible interface of the spreading drop. To characterize the final size and shape of the drop, we perform systematic experiments by varying the drop volume and the glycerol-water volume fraction. In addition, we have developed scaling arguments for the drop's final radius using key physical forces, and show that the final wavelength is inversely proportional to the Bond number.

Automated summary

We experimentally investigate the interfacial instability that occurs when a water droplet is deposited on a glycerol-water solution. Despite the lack of surface tension to stabilize the undulations, we observe the growth and pinching off of finite-size fingers from the droplet. This behavior is a result of the balance between outward buoyancy and inward Marangoni flow.