Eur. Phys. J. E (2010) 33: 203-210
https://doi.org/10.1140/epje/i2010-10662-7

Regular Article

How a coating is hydrated ahead of the advancing contact line of a volatile solvent droplet

¹ PPMD-SIMM, UMR 7615, CNRS, UPMC, ESPCIParisTech, 10 rue Vauquelin, 75231, Paris, France
² Rhodia Recherches, 52 rue de la Haie Coq, 93300, Aubervilliers, France

^* e-mail: francois.lequeux@espci.fr

Received: 7 April 2010
Revised: 13 July 2010
Published online: 24 October 2010

Abstract

The wettability of coatings is very sensitive to the amount of solvent they may contain. When a droplet of volatile solvent, such as water, is deposited on a substrate, its vapor may quickly condensate just ahead of the contact line. We give an estimation of the extent of solvent uptake by a coating of variable thickness e , in front of an advancing contact line of given velocity U . Depending on the values of e and U , we observe three regimes: at low velocity and for a thin coating, the coating adsorbs a fraction of solvent that can quickly equilibrate across its entire thickness, so that it mainly appears solvophilic, while this is not the case for a thick coating. For high velocities, regardless the coating thickness, the coating ahead of the contact line does not have enough time to adsorb a significant amount of solvent, so that it mainly appears solvophobic. All these phenomena appear to be controlled by a molecular cut-off length.