Spreading and contracting three-component droplets for cleaning high energy surfaces

Marangoni flows are a well established mechanism for inducing droplet spreading and contraction. In this work, we study the behavior of a three-component mixture (ethanol, water, and propylene glycol) on high energy surfaces. Evaporation of the ethanol (most volatile, lowest surface tension) results in a higher surface tension around the perimeter of the droplet and rapid spreading. After ethanol evaporation, water evaporation (next most volatile component, highest surface tension) from the perimeter induces a reversal in the direction of Marangoni flow and droplet contraction. We investigate this ternary parameter space to unravel the interplay of Marangoni flow, capillary flow, and evaporation. The self-expansion and contraction of these droplets make them suitable for cleaning even high energy surfaces.