Seminar über aktuelle Fragen zur Dynamik komplexer Fluide: Capillary Driven Flow

Seminar über aktuelle Fragen zur Dynamik komplexer Fluide

  • Datum: 28.06.2019
  • Uhrzeit: 10:15 - 11:15
  • Vortragende(r): Carmen Lee
  • Department of Physics and Astronomy, McMaster University, Canada
  • Ort: Max-Planck-Institut für Dynamik und Selbstorganisation (MPIDS)
  • Raum: SR 0.77
  • Gastgeber: DCF
  • Kontakt:
The principles of fluid dynamics govern the behaviour of fluids over many orders of magnitudes in length scale, from galaxies to nanoscale coatings on microelectronics. As the length scale of the system becomes smaller, capillary forces begin to overcome the forces. In this talk two different systems will be discussed, where viscous flow is driven by surface tension, and mediated by viscosity.
The first is the study of thin (~100 nm), stepped polymer films. The stability and flow of a thin, viscous film is sensitive to the boundary conditions as the film thickness approaches the nanoscale. Here we probe a liquid-liquid boundary condition: a stepped polymer film (PMMA) is placed above a different, immiscible polymer film (PS). The ensemble is supported by a solid substrate. A schematic of the sample is shown in figure 1. The temporal evolution of the air-polymer interface, as well as the polymer-polymer interface were studied using atomic force microscopy. The polymer-polymer interface was exposed using a selective solvent to remove the top film. Experimental results show that the step at the air-polymer interface levels to minimize the excess surface area, and that there is substantial deformation at the interface between the two polymers during the levelling process.
The second system is one inspired by Nature. In arid climates, Nature has developed an efficient method of harvesting water from air. Organisms, like cacti, are covered in multitudes of needle-like conical fibers. Water droplets that condense on the tip of the fiber will be spontaneously driven toward the base. The conical shape is the mechanism responsible for the motion. In Nature, it is rare for a single droplet to condense onto a fiber; in this talk, we examine the motion of multiple droplets on a conical glass fiber. By coating the fiber in a uniform liquid film, we use the Plateau Rayleigh instability to form multiple droplets along the fiber. In doing so, we are able to study: 1) the motion of multiple droplets, 2) the pattern that the droplets form, as well as 3) when droplets merge on the fiber. An example of droplets merging together is shown in figure 2. Using simple surface tension arguments, we are able to capture the dynamics of coalescence. Thus, we can understand the basic principles of how droplets collect on organisms to best harvest water.
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