title: Universal spreading of water drops on complex surfaces.
abstract: A drop of water spreads very rapidly just after it is gently deposited on a solid surface. Here we experimentally investigate how these early stages of spreading are influenced by different types of surface complexity. In particular, we consider micro-textured substrates, chemically striped substrates and soft substrates. For all these complex substrates, it is found that there always exists an inertial regime where the radius r of the wetted area grows as r ∼ t(1/2). For perfectly wetting substrates, this regime extends over several decades in time, whereas we observe a deviation from a pure power-law for partially wetting substrates. Our experiments reveal that even the cross-over from the 1/2 power law to the final equilibrium radius displays a universal dynamics. This cross-over is governed only by the final contact angle, regardless of the details of the substrate.
authors.affiliation: Physics of Fluids Group, MESA+ Institute for Nanotechnology, J. M. Burgers Centre for Fluid Dynamics, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands. j.h.snoeijer@utwente.nl.
authors.forename: B B J
authors.initials: BB
authors.lastname: Stapelbroek
authors.forename: H P
authors.initials: HP
authors.lastname: Jansen
authors.forename: E S
authors.initials: ES
authors.lastname: Kooij
authors.forename: J H
authors.initials: JH
authors.lastname: Snoeijer
authors.forename: A
authors.initials: A
authors.lastname: Eddi