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    Probing the nanoscale: the first contact of an impacting drop

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    LiVakarelskiThoroddsen_JFM2015.pdf
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    Type
    Article
    Authors
    Li, Erqiang cc
    Vakarelski, Ivan Uriev cc
    Thoroddsen, Sigurdur T cc
    KAUST Department
    Clean Combustion Research Center
    High-Speed Fluids Imaging Laboratory
    Mechanical Engineering Program
    Physical Science and Engineering (PSE) Division
    Date
    2015-11-16
    Online Publication Date
    2015-11-16
    Print Publication Date
    2015-12
    Permanent link to this record
    http://hdl.handle.net/10754/583813
    
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    Abstract
    When a drop impacts onto a solid surface, the lubrication pressure in the air deforms its bottom into a dimple. This makes the initial contact with the substrate occur not at a point but along a ring, thereby entrapping a central disc of air. We use ultra-high-speed imaging, with 200 ns time resolution, to observe the structure of this first contact between the liquid and a smooth solid surface. For a water drop impacting onto regular glass we observe a ring of microbubbles, due to multiple initial contacts just before the formation of the fully wetted outer section. These contacts are spaced by a few microns and quickly grow in size until they meet, thereby leaving behind a ring of microbubbles marking the original air-disc diameter. On the other hand, no microbubbles are left behind when the drop impacts onto molecularly smooth mica sheets. We thereby conclude that the localized contacts are due to nanometric roughness of the glass surface, and the presence of the microbubbles can therefore distinguish between glass with 10 nm roughness and perfectly smooth glass. We contrast this entrapment topology with the initial contact of a drop impacting onto a film of extremely viscous immiscible liquid, where the initial contact appears to be continuous along the ring. Here, an azimuthal instability occurs during the rapid contraction at the triple line, also leaving behind microbubbles. For low impact velocities the nature of the initial contact changes to one initiated by ruptures of a thin lubricating air film.
    Citation
    Probing the nanoscale: the first contact of an impacting drop 2015, 785 Journal of Fluid Mechanics
    Publisher
    Cambridge University Press (CUP)
    Journal
    Journal of Fluid Mechanics
    DOI
    10.1017/jfm.2015.643
    Additional Links
    http://www.journals.cambridge.org/abstract_S0022112015006436
    ae974a485f413a2113503eed53cd6c53
    10.1017/jfm.2015.643
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program; Clean Combustion Research Center

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