Water droplet friction and rolling dynamics on superhydrophobic surfaces

Matilda Backholm*, Daniel Molpeceres, Maja Vuckovac, Heikki Nurmi, Matti Hokkanen, Ville Jokinen, Jaakko Timonen, Robin Ras

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Superhydrophobicity is a remarkable surface property found in nature and mimicked in many engineering applications, including anti-wetting, anti-fogging, and anti-fouling coatings. As synthetic superhydrophobic coatings approach the extreme non-wetting limit, quantification of their slipperiness becomes increasingly challenging: although contact angle goniometry remains widely used as the gold standard method, it has proven insufficient. Here, micropipette force sensors are used to directly measure the friction force of water droplets moving on super-slippery superhydrophobic surfaces that cannot be quantified with contact angle goniometry. Superhydrophobic etched silicon surfaces with tunable slipperiness are investigated as model samples. Micropipette force sensors render up to three orders of magnitude better force sensitivity than using the indirect contact angle goniometry approach. We directly measure a friction force as low as 7 ± 4 nN for a millimetric water droplet moving on the most slippery surface. Finally, we combine micropipette force sensors with particle image velocimetry and reveal purely rolling water droplets on superhydrophobic surfaces.
Original languageEnglish
Article number64
Number of pages8
JournalCommunications Materials
Volume1
Issue number1
DOIs
Publication statusPublished - 15 Sep 2020
MoE publication typeA1 Journal article-refereed

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