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 microfluidics.
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Dieter
D
't Mannetje
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Somnath
S
Ghosh
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Rudy
R
Lagraauw
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Simon
S
Otten
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Arjen
A
Pit
Department of Applied Physics, Mesoscopic Transport Properties Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Christian
C
Berendsen
Department of Applied Physics, Mesoscopic Transport Properties Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Jos
J
Zeegers
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Dirk
D
van den Ende
University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede, The Netherlands.
Frieder
F
Mugele