Speaker
Description
We report on the dynamics of a pair of droplets, connected together by a microchannel and undergoing constant contact radius evaporation. We see that for droplets of equal contact radii, unidirectional flow can arise from differences in droplet geometry and results in the larger droplet feeding the smaller droplet as they evaporate out. However, for droplets of unequal contact radii, the shape of the droplet pair can invert during the evaporation process, causing a reversal in the flow direction. A stability analysis shows that the droplets’ transportation on a short-time scale is underpinned by a supercritical pitchfork bifurcation. However, over a long time-scale, the loss of volume to evaporation allows the system to step through a series of states, corresponding to quasi-steady solutions of the droplet geometry on a short-time scale. If the symmetry of the contact radii is broken, the supercritical pitchfork bifurcation unfolds. Thus, we show that the droplet shape inversion and the associated flow reversal can be understood as a jump from the disconnected to connected branch of the bifurcation, which establishes symmetry breaking as a mechanism to induce evaporation-driven flow reversal in connected droplets.