How a coating is hydrated ahead of the advancing contact line of a volatile solvent droplet
PPMD-SIMM, UMR 7615, CNRS, UPMC, ESPCIParisTech, 10 rue Vauquelin, 75231, Paris, France
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Revised: 13 July 2010
Published online: 24 October 2010
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.
© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg, 2010