《Drops on a conical wire》.pdf

c J. Fluid Mech. (2004), vol. 510, pp. 29–45. 2004 Cambridge University Press 29 DOI: 10.1017/S0022112004009152 Printed in the United Kingdom Drops on a conical wire ´ ´ ´ By E L I S E L O R E N C E A U AND D A V I D Q U E R E ` ´ Laboratoire de Physique de la Matiere Condensee, UMR 7125 du CNRS, ` College de France, 75231 Paris Cedex 05, France (Received 3 June 2003 and in revised form 31 December 2003) We study experimentally the behaviour of a drop deposited on a conical fibre. It is shown that for wetting liquids, such a drop spontaneously moves towards the region of lower curvature. The driving force is measured and shown to be a gradient of Laplace pressure, which allows us to characterize the dynamics of these self-propelling drops. We conclude by discussing the efficiency of this device for drying a solid initially coated with a liquid film. 1. Introduction Asymmetric droplets often have the property of moving, and different ways for generating such motions have been described. Bouasse suggested that a slug in a conical capillary tube should move toward the region of small radius (Bouasse 1924). Weislogel characterized the motion of a drop deposited across the interface between two substrates of different chemical nature (Weislogel 1997). Bain, Burnett-Hall Montgomerie (1994) and Domingues dos Santos Ondarc¸uhu (1995) invented a dynamic version of that, in which the motion itself keeps alive a contrast in wettability