Regensburg 2013 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 44: Wetting, Micro- and Nanofluidics

CPP 44.8: Vortrag

Donnerstag, 14. März 2013, 17:30–17:45, H39

Marangoni Modified Drop Fusion and Drop Motion — Stefan Karpitschka and •Hans Riegler — MPI für Kolloid- und Grenzflächenforschung, Potsdam, Germany

Sessile droplets on solid surfaces will fuse due to capillary forces. The droplet fusion can be delayed if the droplets consist of different (but still completely miscible) liquids. Quite unexpected, even after initial contact at the three phase line, the main droplet bodies remain separated. The droplets are connected only through a neck via a thin liquid film and move together over the substrate surface [1]. This non-coalescing state can last up to minutes. Its origin are the different surface energies of the liquids: The difference induces a Marangoni flow between the droplets which keeps them separate [2]. Based on new experiments, we present -- for the first time -- an analytical treatment in the framework of a thin film description. The key ingredient is a balance of advective and diffusive transport mechanisms in the vicinity of the neck, which induces a Marangoni flow. By piece-wise asymptotic matching of meso- and microscopic solutions we determine the global free surface topology and the capillary number [3]. We find traveling wave solutions in quantitative agreement with the experimental observations. The findings are generally relevant for (shallow, steady-state) free surface flows that involve (are caused by) surface tension gradients (e.g. due to local compositional variations).

[1] H. Riegler, P. Lazar, Langmuir 24, 6395 (2008).

[2] S. Karpitschka, H. Riegler, Langmuir 26, 11823 (2010).

[3] S. Karpitschka, H. Riegler, PRL 109, 066103 (2012).