Droplet suction on porous mediaL. Bacri and F. Brochard-Wyart
Laboratoire Physico-Chimie Curie - Unité Mixte de Recherche 168, Centre National de la Recherche Scientifique/Institut Curie, 26 rue d'Ulm, 75248 Paris Cedex 05, France (In collaboration with Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France.)
(Received 19 January 2000)
We study the forced aspiration of small ( mm) and large ( cm) liquid drops, deposited on prewetted porous membranes, and pumped mechanically with a constant current J. Two kinds of membranes are used where the pores are i) disconnected, cylindrical and calibrated or ii) interconnected "sponge-like". Whatever the size of the drops and the intensity J of the current, two suction regimes are observed versus time: 1) a "locked" regime, when the drop is pinned, with a dynamic contact angle decreasing from advancing ( ) to finite receding ( ) contact angle; 2) an "unlocked" regime, where the contour line recedes with a constant contact angle closed to . In both regimes, the shape of the drop remains quasistatic, during the suction process, i.e. a spherical cap for small drops and a flat "gravity pancake" for large ones.
68.45.Gd - Wetting.
47.55.Mh - Flows through porous media.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2000