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IRTG / Soft Matter Science
Freiburger Materialforschungszentrum
Stefan-Meier-Str. 21
79104 Freiburg, Germany

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You are here: Home Events Dr. Joshua McGraw "Influence of slip and precursor thickness on polymer microdroplet equilibration dynamics"

Dr. Joshua McGraw "Influence of slip and precursor thickness on polymer microdroplet equilibration dynamics"

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Experimental Physics, Universität des Saarlandes, Saarbrücken, Germany

  • Seminar
When Jul 30, 2014
from 02:15 PM to 03:00 PM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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When a liquid droplet is placed into contact with a flat surface, as when paint lands on a smooth surface, it is in general out of equilibrium. Specifically, the angles at which droplets meet the flat surface will not be those governed by the Young-Dupré equation -- the liquid must flow to achieve equilibrium. This flow often entails the motion of a contact line which, though ubiquitous, leads to a stress divergence if a typical hydrodynamic model is used. The presence of precursor films, and/or slip at the solid-liquid interface can relieve this divergence. The experimental studies to be discussed in this talk employ microscopic polymer droplets placed on planar surfaces with non-equilibrium contact angles. In the first case, we sweep the precursor film thickness on which droplets spread to form flat films. Not only are the dynamics of droplet spreading greatly enhanced by thicker precursors, thicker layers are also accompanied by a crossover in the spreading law. These observations are consistent with a hydrodynamic model in the lubrication approximation. We also prepare substrates with variable slip lengths, in our case giving rise to retracting rather than spreading droplets. We find that changing the slip condition results in dramatic changes to the temporal and morphological path these tiny droplets take toward their equilibrium spherical cap shapes.

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