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

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 an...

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Bibliographic Details
Published in:Soft matter 2018, Vol.14 (37), p.7586-7596
Main Authors: Langley, Kenneth R, Li, Er Qiang, Vakarelski, Ivan U, Thoroddsen, Sigurdur T
Format: Article
Language:English
Subjects:
Appliance industry
Bubbles
Coalescing
Entrapment
Flat surfaces
Hydrophobicity
Organic chemistry
Roughness
Scaling
Scaling laws
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Summary: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.
ISSN:1744-683X
1744-6848
DOI:10.1039/c8sm01070f