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    Impact of ultra-viscous drops: air-film gliding and extreme wetting

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    Type
    Article
    Authors
    Langley, Kenneth cc
    Li, Erqiang 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
    2017-01-23
    Online Publication Date
    2017-01-23
    Print Publication Date
    2017-02
    Permanent link to this record
    http://hdl.handle.net/10754/622896
    
    Metadata
    Show full item record
    Abstract
    A drop impacting on a solid surface must push away the intervening gas layer before making contact. This entails a large lubricating air pressure which can deform the bottom of the drop, thus entrapping a bubble under its centre. For a millimetric water drop, the viscous-dominated flow in the thin air layer counteracts the inertia of the drop liquid. For highly viscous drops the viscous stresses within the liquid also affect the interplay between the drop and the gas. Here the drop also forms a central dimple, but its outer edge is surrounded by an extended thin air film, without contacting the solid. This is in sharp contrast with impacts of lower-viscosity drops where a kink in the drop surface forms at the edge of the central disc and makes a circular contact with the solid. Larger drop viscosities make the central air dimple thinner. The thin outer air film subsequently ruptures at numerous random locations around the periphery, when it reaches below 150 nm thickness. This thickness we measure using high-speed two-colour interferometry. The wetted circular contacts expand rapidly, at orders of magnitude larger velocities than would be predicted by a capillary-viscous balance. The spreading velocity of the wetting spots is independent of the liquid viscosity. This may suggest enhanced slip of the contact line, assisted by rarefied-gas effects, or van der Waals forces in what we call extreme wetting. Myriads of micro-bubbles are captured between the local wetting spots.
    Citation
    Langley K, Li EQ, Thoroddsen ST (2017) Impact of ultra-viscous drops: air-film gliding and extreme wetting. Journal of Fluid Mechanics 813: 647–666. Available: http://dx.doi.org/10.1017/jfm.2016.840.
    Sponsors
    The work reported herein was funded by King Abdullah University of Science and Technology (KAUST).
    Publisher
    Cambridge University Press (CUP)
    Journal
    Journal of Fluid Mechanics
    DOI
    10.1017/jfm.2016.840
    Additional Links
    https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/div-classtitleimpact-of-ultra-viscous-drops-air-film-gliding-and-extreme-wettingdiv/798BDD556D6008324CB300EC56F80F16
    ae974a485f413a2113503eed53cd6c53
    10.1017/jfm.2016.840
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program; Clean Combustion Research Center

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