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

Kenneth Langley, Erqiang Li, Ivan Uriev Vakarelski, Sigurdur T Thoroddsen

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

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.
Original languageEnglish (US)
Pages (from-to)7586-7596
Number of pages11
JournalSoft Matter
Volume14
Issue number37
DOIs
StatePublished - 2018

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