Trapping of drops by wetting defects

Controlling the motion of drops on solid surfaces is crucial in many natural phenomena and technological processes including the collection and removal of rain drops, cleaning technology and heat exchangers. Topographic and chemical heterogeneities on solid surfaces give rise to pinning forces that can capture and steer drops in desired directions. Here we determine general physical conditions required for capturing sliding drops on an inclined plane that is equipped with electrically tunable wetting defects. By mapping the drop dynamics on the one-dimensional motion of a point mass, we demonstrate that the trapping process is controlled by two dimensionless parameters, the trapping strength measured in units of the driving force and the ratio between a viscous and an inertial time scale. Complementary experiments involving superhydrophobic surfaces with wetting defects demonstrate the general applicability of the concept. Moreover, we show that electrically tunable defects can be used to guide sliding drops along actively switchable tracks—with potential applications in microfluidic

Dynamic trapping of sliding drops on wetting defects

Abstract Submitted for the DFD14 Meeting of The American Physical Society Dynamic trapping of sliding drops on wetting defects ANDREA CAVALLI, University of Twente, MICHIEL MUSTERD, TU Delft, DIETER ’T MANNETJE, DIRK VAN DEN ENDE, FRIEDER MUGELE, University of Twente —We present a numerical analysis of the dynamic interaction of a sessile sliding drop with a wetting defect. Our three-dimensional model, developed with OpenFOAM, allows us to describe inertial and viscous effects, as well as the internal degrees of freedom of the droplet. We observe that the ability of a drop to deform and stretch enhances the strength and range of the wetting defect, in comparison to a simplified analytic description. We further investigate the role of the strength, size and steepness of the defect in retaining the drop. Finally, we compare our simulations with trapping experiments on electrowetting obstacles, observing a quantitative agreement. This shows that the trapping of sliding drops follows a universal behavior, which is not significantly affected by the nature of the defect. Andrea Cavalli University of Twente Date submitted: 31 Jul 2014 Electronic form version 1.