4.8 Article

Viscosity-enhanced droplet motion in sealed superhydrophobic capillaries

Journal

SCIENCE ADVANCES
Volume 6, Issue 42, Pages -

Publisher

AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/sciadv.aba5197

Keywords

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Funding

  1. Academy of Finland [Centres of Excellence Programme (2014-2019)]
  2. European Commission [626954]
  3. European Research Council [725513]
  4. Academy of Finland [309237]
  5. European Research Council (ERC) [725513] Funding Source: European Research Council (ERC)
  6. Academy of Finland (AKA) [309237, 309237] Funding Source: Academy of Finland (AKA)

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It is well known that an increased viscosity slows down fluid dynamics. Here we show that this intuitive rule is not general and can fail for liquids flowing in confined liquid-repellent systems. A gravity-driven, highly viscous glycerol droplet inside a sealed superhydrophobic capillary is moving more than 10 times faster than a water droplet with three-orders-of-magnitude lower viscosity. Using tracer particles, we show that the low-viscosity droplets are rapidly rotating internally, with flow velocities greatly exceeding the center-of-mass velocity. This is in stark contrast to the faster moving high-viscosity droplets with nearly vanishing internal flows. The anomalous viscosity-enhanced flow is caused by a viscosity-suppressed deformation of the droplet-air interface and a hydroand aerodynamic coupling between the droplet and the air trapped within the micro/nanostructures (plastron). Our work demonstrates the unexpected role of the plastron in controlling fluid flow beyond the mere reduction in contact area and friction.

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