Motion of water droplets on oil infused surfaces

Controlling the motion of water droplets on solid surfaces has broad technological implications ranging from microfluidics to thermal management. Past approaches utilized topography and chemical composition gradients to manipulate the motion of droplets. Here we show that the motion of droplets on oil infused surfaces can be triggered via asymmetry of the wetting ridge. Our experimental results show that neighboring droplets exert force on each other through their wetting ridge. This interaction causes droplets to coalesce and self propel by releasing free surface energy. Importantly, our experiments show that the motion of water droplets on slippery oil infused surfaces is not random as has been hypothesized in past studies. Instead, the oleoplaning droplets select their path such that the force required to overcome viscous dissipation is minimum. Consequently, droplets move away from oil depleted regions where the lubrication oil thickness is small and the resistance to motion is large. This ``sensing'' ability of droplets to the thickness of lubrication oil enables them to maneuver by avoiding prior oil depleted paths. This study provides new mechanistic insight into the motion of water droplets on oil infused surfaces.

The authors acknowledgments funding from the Wyss Institute.