Encapsulation of Droplets Using Cusp Formation Behind a Drop Rising in a Non-Newtonian Fluid

The rising of an oil drop in a non-Newtonian viscous solution is studied experimentally. The oil that we used was an alimentary corn oil, and the surrounding fluid is a water/glycerol polyacrylamide solution. In this case, the shape of the ascending drop is strongly affected by the non-Newtonian properties of the surrounding liquid. We found that the so-called velocity discontinuity phenomena is observed for drops larger than a certain critical size. Beyond the critical velocity, the formation of a long tail is observed, from which small droplets are continuously emitted. We determined that the fragmentation of the tail results mainly from the effect of capillary effects. We explore the idea of using this configuration as a new encapsulation technique, where the size and frequency of droplets are directly linked to the volume of the main rising drop, for the particular pair of fluids used. Those experimental results could lead to other experiments, which could help to predict the droplets deposition dynamics by tuning the two fluids properties, and adjusting only the volume of the main drop.