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

34 Scopus citations


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
Issue number37
StatePublished - 2018

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): URF/1/2621-01-01
Acknowledgements: The authors would like to thank Peter Hicks for useful discussions. The work reported herein was supported by funding from King Abdullah University of Science and Technology (KAUST) under Grant No. URF/1/2621-01-01. E. Q. Li acknowledges the Thousand Young Talents Program of China, the National Natural Science Foundation of China (Grant No. 11772327, 11642019, & 11621202) and Fundamental Research Funds for the Central Universities (Grant No. WK2090050041).


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