68th Annual Meeting of the APS Division of Fluid Dynamics (November 22, 2015 — November 24, 2015)

V0052: Can a droplet hop on a rigid surface?

  • Thomas Schutzius, ETH-Zurich
  • Stefan Jung, ETH-Zurich
  • Gustav Graeber, ETH-Zurich
  • Tanmoy Maitra, ETH-Zurich
  • Dimos Poulikakos, ETH-Zurich
DOI: https://doi.org/10.1103/APS.DFD.2015.GFM.V0052

In this video, we show how droplets in contact with superhydrophobic surfaces can exhibit fascinating behavior when we shift their environment from familiar atmospheric conditions to a low-pressure state. Specifically, droplets are shown to spontaneously levitate and exhibit hopping behavior. After the initial levitation, sequential droplet-substrate collisions accelerate the droplet, as revealed by high-speed photography, resulting in restitution coefficients greater than unity even though the surface is rigid. Such information facilitates construction of a simple model that gives insight into the levitation and hopping mechanisms. We attribute the behavior to the existence of an overpressure between the droplet and substrate -- the result of a high vaporization flux while surface texture and substrate adhesion act to restrict vapor flow. While such behavior is applicable only to low-pressure environments, it illustrates how understanding droplet-surface interactions can guide surface texture design to prohibit liquid retention on surfaces.

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