title: Not spreading in reverse: The dewetting of a liquid film into a single drop.
abstract: Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet-a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction.
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, U.K.
authors.forename: Andrew M J
authors.identifier: 0000-0003-3338-1287
authors.initials: AM
authors.lastname: Edwards
authors.affiliation: Smart Materials and Surfaces Laboratory, Department of Physics and Electrical Engineering, Northumbria University, Ellison Place, Newcastle upon Tyne NE1 8ST, U.K.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Ledesma-Aguilar
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, U.K.
authors.forename: Michael I
authors.identifier: 0000-0003-4231-1002
authors.initials: MI
authors.lastname: Newton
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, U.K.
authors.forename: Carl V
authors.identifier: 0000-0002-1559-3238
authors.initials: CV
authors.lastname: Brown
authors.affiliation: Smart Materials and Surfaces Laboratory, Department of Physics and Electrical Engineering, Northumbria University, Ellison Place, Newcastle upon Tyne NE1 8ST, U.K.
authors.forename: Glen
authors.identifier: 0000-0002-8519-7986
authors.initials: G
authors.lastname: McHale
mesh_terms: D057446:Hydrodynamics; D007700:Kinetics; D008956:Models, Chemical; D012996:Solutions / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D017155:Wettability
chemical_list: D012996:Solutions; D013501:Surface-Active Agents
keywords: Dewetting; contact-line dynamics; dielectrowetting; slip