Issue 38, 2024

Probing the physical origins of droplet friction using a critically damped cantilever

Abstract

Previously, we and others have used cantilever-based techniques to measure droplet friction on various surfaces, but typically at low speeds U < 1 mm s−1; at higher speeds, friction measurements become inaccurate because of ringing artefacts. Here, we are able to eliminate the ringing noise using a critically damped cantilever. We measured droplet friction on a superhydrophobic surface over a wide range of speeds U = 10−5–10−1 m s−1 and identified two regimes corresponding to two different physical origins of droplet friction. At low speeds U < 1 cm s−1, the droplet is in contact with the top-most solid (Cassie–Baxter), and friction is dominated by contact-line pinning with Ffric force that is independent of U. In contrast, at high speeds U > 1 cm s−1, the droplet lifts off the surface, and friction is dominated by viscous dissipation in the air layer with FfricU2/3 consistent with Landau–Levich–Derjaguin predictions. The same scaling applies for superhydrophobic and underwater superoleophobic surfaces despite their very different surface topographies and chemistries, i.e., the friction scaling law derived here is universal.

Graphical abstract: Probing the physical origins of droplet friction using a critically damped cantilever

Supplementary files

Article information

Article type
Paper
Submitted
18 May 2024
Accepted
02 Sep 2024
First published
02 Sep 2024
This article is Open Access
Creative Commons BY license

Soft Matter, 2024,20, 7583-7591

Probing the physical origins of droplet friction using a critically damped cantilever

S. Arunachalam, M. Lin and D. Daniel, Soft Matter, 2024, 20, 7583 DOI: 10.1039/D4SM00601A

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