Berlin 2018 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 17: Focus: Droplets (joint session DY/CPP)

DY 17.3: Talk

Monday, March 12, 2018, 16:00–16:15, BH-N 334

Drying Teardrops — •Alvaro Marin¹, Stefan Karpitschka², Christian Diddens³, Massimiliano Rossi⁴, Christian J. Kähler⁴, Diego Noguera-Marin⁵, and Miguel A. Rodriguez-Valverde⁵ — ¹Max Planck + University of Twente Center for Complex Fluid Dynamics, The Netherlands — ²Max Planck Center for Dynamics and Self-Organization, Germany — ³Physics of Fluids, University of Twente, The Netherlands — ⁴Bundeswehr University Munich, Neubiberg, Germany — ⁵Biocolloid and Fluid Physics group, University of Granada, Spain

Salt can be found in different forms in almost any evaporating droplet in nature, our homes and in our own tears. Dried teardrops present an amazing variety of forms, shapes and crystals (even for the same person), but they all have something in common: a ring-shaped stain. In this talk we will address a model teardrop system consisting of an evaporating water sessile droplet with sodium chloride concentrations from 1 mM up to 100 mM. With experimental measurements and numerical simulations we can show that the transport of liquid in this system differs strongly from 'sweet' evaporating water droplets: the liquid flows in the inverse direction due to strong Marangoni stresses at the surface. Such an effect has crucial consequences to the deposition of salt, its crystallization and to the formation of the ring-shaped stains. In summary, our aim is to show that other mechanisms different than the famous ``coffee-stain effect'' can yield ring-shaped stains in evaporating sessile droplets.