Seminar über aktuelle Fragen zur Dynamik komplexer Fluide: Taylor dispersion governs the composition of Marangoni contracted droplets

Seminar über aktuelle Fragen zur Dynamik komplexer Fluide

  • Date: Nov 20, 2020
  • Time: 10:15 AM - 11:15 AM (Local Time Germany)
  • Speaker: Stefan Karpitschka
  • MPI-DS
  • Location: Max-Planck-Institut für Dynamik und Selbstorganisation (MPIDS)
  • Room: Video conference at, Meeting ID: 980 3913 9623, Passcode: 050762
  • Host: DCF
  • Contact:
Marangoni contraction of sessile droplets occurs when a binary mixture of volatile liquids is placed on a high-energy surface. Although the surface is wetted completely by the mixture and its components, a quasi-stationary non-vanishing contact angle is observed. This is seeming contradiction is caused by Marangoni flows that are driven by evaporative depletion of the volatile component near the edge of the droplet. If the residual component has a lower surface tension, Marangoni flows are directed toward the center of the droplet, leading to a contraction until they are balanced by opposing capillary flows. This mechanism is widely used for drying and cleaning in technological applications, for instance in the wet processing of semiconductor circuits, but its physical explanation remains debated in literature. Here we show that the compositional evolution of such droplets is governed by Taylor dispersion. Breaking a long-lived paradigm, we demonstrate that Taylor dispersion can consistently be included in a long wave expansion for the evolution of thin films. Coupled to a non-local description of diffusion limited evaporation, this model quantitatively reproduces not only the apparent shape of Marangoni contracted droplets, but also their internal flows.
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