Viscosity-enhanced droplet motion in sealed superhydrophobic capillaries

Maja Vuckovac, Matilda Backholm, Jaakko V.I. Timonen*, Robin H.A. Ras

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

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 hydro- and 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.

Original languageEnglish
Article numbereaba5197
Number of pages8
JournalScience Advances
Volume6
Issue number42
DOIs
Publication statusPublished - Oct 2020
MoE publication typeA1 Journal article-refereed

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