8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P6.4Fri 911:10-14:00Soap film motion in tubes : definition of an influencelengthIsabelle Cantat 1 and Benjamin Dollet 21 Institut de Physique de Rennes, bat 11A, campus de Beaulieu, 35042, Rennes cedex,France2 Institut de Physique de Rennes, Rennes cedex, FranceThe motion of a liquid meniscus sliding over a wet wall is involved in several important practicalsituations among which dip coating, bubbles (or droplets) motion in microfluidic channels andfoam friction on solid boundaries. The problem has first been studied by Landau and Levich(1942) and Derjaguin (1933) (LLD) for a solid plate pulled out of a liquid bath at small velocity.For pure liquids, the dynamics is controled by the dynamical meniscus, of lateral extension L LLD ,that forms between the static meniscus, at rest, and the wetting film, moving at the plate velocity.We study the case of transverse film motion in glass tube [Dollet2010]. For surfactant having alarge surface dilatational elasticity, we show that the motion is transmitted over a macroscopiclength L ∞ in the wetting film ahead of it. We measureL ∞ by interferometry techniques and showthat L ∞ > L LLD and that this influence length can reach several centimeters. From systematicmeasurements, we show that L ∞ is a decreasing function of the velocity, and an increasingfunction of the flat wetting film thickness. Furthermore, at high velocity the transverse film motionbecomes unsteady, becoming reminiscent of stick-slip, which is highly unexpected for a fluid (thetransverse film) sliding on a fluid (the wetting film). The experimental results are compared toanalytical and numerical results, that take into account the surface tension variations induced bythe film motion.[Dollet2010] B. Dollet, I. Cantat. Deformation of soap films pushed through tubes at highvelocity. J. Fluid. Mech. vol 652 p. 529-539 (2010).[Scheid2010] B. Scheid, J. Delacotte, B. Dollet, E. Rio, F. Restagno, E. A. van Nierop, I. Cantat,D. Langevin and H. A. Stone, The role of surface rheology in liquid film formation. Europhys.Lett. vol 90 p. 24002 (2010)4