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Issue 37, 2018
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The air entrapment under a drop impacting on a nano-rough surface

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We study the impact of drops onto a flat surface with a nano-particle-based superhydrophobic coating, focusing on the earliest contact using 200 ns time-resolution. A central air-disc is entrapped when the drop impacts the surface, and when the roughness is appropriately accounted for, the height and radial extent of the air-disc follow the scaling laws established for impacts onto smooth surfaces. The roughness also modifies the first contact of the drop around the central air-disc, producing a thick band of micro-bubbles. The initial bubbles within this band coalesce and grow in size. We also infer the presence of an air-film residing inside the microstructure, at radial distances outside the central air-disc. This is manifest by the sudden appearance of microbubbles within a few microseconds after impact. The central air-disc remains pinned on the roughness, unless it is chemically altered to make it superhydrophilic.

Graphical abstract: The air entrapment under a drop impacting on a nano-rough surface

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Article information

24 May 2018
22 Jul 2018
First published
02 Aug 2018

This article is Open Access

Soft Matter, 2018,14, 7586-7596
Article type

The air entrapment under a drop impacting on a nano-rough surface

K. R. Langley, E. Q. Li, I. U. Vakarelski and S. T. Thoroddsen, Soft Matter, 2018, 14, 7586 DOI: 10.1039/C8SM01070F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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