Berlin 2018 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 17: Focus: Droplets (joint session DY/CPP)
DY 17.1: Talk
Monday, March 12, 2018, 15:30–15:45, BH-N 334
Marangoni Contraction of Evaporating Sessile Droplets of Binary Mixtures — •Stefan Karpitschka1, Ferenc Liebig2, and Hans Riegler3 — 1Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, 37077 Göttingen — 2Institute of Chemistry, University of Potsdam, Karl-Liebknecht-Straße 24-25, 14476 Potsdam — 3Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam
The evaporation of sessile droplets of mixtures is a ubiquitous natural and industrial process, relevant, e.g., for cleaning/drying of semiconductor surfaces or for ink-jet printing. For binary mixtures, the component with the higher vapor pressure will usually evaporate faster and thus deplete from the contact line region of a droplet. In general, different liquids have different surface tensions. Thus, evaporation causes surface tension gradients and Marangoni flows. Here we investigate the impact of evaporation on the wetting behavior of binary mixtures [Langmuir 33, 4682 (2017)]. We measure non-zero apparent contact angles even if both liquid components individually wet the substrate completely. Simulations show that the interplay of Marangoni flow, capillary flow, diffusive transport, and evaporative losses can establish a quasi-stationary drop profile with an apparent nonzero contact angle. In good agreement with experiments, we reveal a previously unknown universal power-law relation between the apparent contact angle and the relative undersaturation of the atmosphere, which can be inferred from the scaling analysis of the hydrodynamic-evaporative evolution equations.