Elasto-capillary interaction of liquid drops

Abstract eng:
We study the interaction between sessile drops on a soft substrate. When millimetric liquid drops run down a soft, vertical surface under gravity, we notice deviation of their trajectories from straight line as two drops approach each other. Remarkably, if the wall is very thick drops always attract and coalesce, whereas two similar drops on a thin layer give rise to a short-ranged repulsion. We develop force-distance curves from experimentally measured drop trajectories and perform a free energy minimisation that unravels the underlying mechanism of drop-drop interaction. Importantly, we show that the interplay between capillarity and bulk elasticity of the soft substrate governs the nature of the interaction force.

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