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Bouncing behaviors of an oil droplet in a stratified liquid

ORAL

Abstract

As we had found in Li et al, \textit{Phys. Rev. Lett.} (2019), an oil droplet is able to repeatedly first sink and then bounce up in a vertically stratified ethanol-water mixture. The Marangoni flow at the droplet-liquid interface, caused by the solute (ethanol) gradient, provides the propulsion for the upwards jump. We now further elucidate the mechanism and explore the phase space. Specifically, we find that as the droplet jumps up to the lighter ethanol-rich region, it gets harder for the propelling droplet to overcome its own weight, until finally it stops. At this maximum height, the Marangoni flow continues to propel, homogenizing its surrounding liquid, thus decreasing the propulsion itself, until it ceases. The droplet then sinks while dragging down this uniform liquid layer with it. We find that this uniform ``shielding'' layer eventually vanishes, mainly because of diffusion, so that the droplet bounces up again, continuing the cycle. It is also found that the maximum height increases with decreasing the droplet size.

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Authors

  • Yanshen Li

    University of Twente

  • Christian Diddens

    PoF - University of Twente, The Netherlands, University of Twente

  • Lijun Thayyil Raju

    University of Twente

  • Xuehua Zhang

    Department of Chemical \& Materials Engineering, University of Alberta; Physics of Fluids Group, University of Twente, University of Alberta

  • Kai Leong Chong

    Univ of Twente, University of Twente

  • Andrea Prosperetti

    U Houston, University of Houston

  • Detlef Lohse

    Physics of Fluids Group and Max Planck Center Twente, MESA+ Institute and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217,, Physics of Fluids group, University of Twente, Physics of Fluids Group, University of Twente, Univ of Twente, PoF - University of Twente, The Netherlands, Twente University, Physics of Fluids Group, University of Twente; Max Planck Institute for Dynamics and Self-Organization, University of Twente