Drop propulsion in tapered tubesP. Renvoisé1, J. W. M. Bush1, M. Prakash2 and D. Quéré3
1 Department of Mathematics, MIT - 77 Massachusetts Avenue, Cambridge, MA 02139, USA
2 Center for Bits and Atoms, MIT - 20 Ames Street, Cambridge, MA 02139, USA
3 PMMH, UMR 7636 du CNRS, ESPCI - 10 rue Vauquelin, 75005 Paris, France, EU
received 22 April 2009; accepted in final form 3 June 2009; published June 2009
published online 9 July 2009
We present the results of a combined experimental and theoretical investigation of the motion of wetting droplets in tapered capillary tubes. We demonstrate that drops may move spontaneously towards the tapered end owing to the Laplace pressure gradient established along their length. The influence of gravity on this spontaneous motion is examined by studying drop motion along a tilted tube with its tapered end pointing upwards. Provided the tube taper varies, an equilibrium height may be achieved in which the capillary force is balanced by the drop's weight. We deduce the family of tube shapes that support a stable equilibrium.
47.55.D- - Drops and bubbles.
47.55.N- - Interfacial flows.
© EPLA 2009