title: Droplets move over viscoelastic substrates by surfing a ridge.
abstract: Liquid drops on soft solids generate strong deformations below the contact line, resulting from a balance of capillary and elastic forces. The movement of these drops may cause strong, potentially singular dissipation in the soft solid. Here we show that a drop on a soft substrate moves by surfing a ridge: the initially flat solid surface is deformed into a sharp ridge whose orientation angle depends on the contact line velocity. We measure this angle for water on a silicone gel and develop a theory based on the substrate rheology. We quantitatively recover the dynamic contact angle and provide a mechanism for stick-slip motion when a drop is forced strongly: the contact line depins and slides down the wetting ridge, forming a new one after a transient. We anticipate that our theory will have implications in problems such as self-organization of cell tissues or the design of capillarity-based microrheometers.
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Karpitschka
authors.affiliation: Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: S
authors.initials: S
authors.lastname: Das
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van Gorcum
authors.affiliation: Physique et Mécanique des Milieux Hétérogènes, UMR 7636 ESPCI-CNRS, Université Paris-Diderot, 10 rue Vauquelin, 75005 Paris, France.
authors.forename: H
authors.initials: H
authors.lastname: Perrin
authors.affiliation: Physique et Mécanique des Milieux Hétérogènes, UMR 7636 ESPCI-CNRS, Université Paris-Diderot, 10 rue Vauquelin, 75005 Paris, France.
authors.forename: B
authors.initials: B
authors.lastname: Andreotti
authors.affiliation: 1] Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands [2] Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: Snoeijer