2D foam coarsening in a microfluidic systemJ. Marchalot1, J. Lambert2, I. Cantat2, P. Tabeling3 and M.-C. Jullien1
1 SATIE, ENS Cachan Bretagne, CNRS, UEB - av Robert Schuman, F-35170 Bruz, France, EU
2 IPR, CNRS UMR 6251, Université de Rennes 1 - Campus Beaulieu, F-35042 Rennes Cedex, France, EU
3 MMN, CNRS UMR 7083, ESPCI - 10 rue Vauquelin, F-75005 Paris, France, EU
received 13 February 2008; accepted in final form 6 August 2008; published September 2008
published online 12 September 2008
We report an experimental study of 2D microfoam coarsening confined in a micrometer scale geometry, the typical bubbles diameter being of the order of 50–100 m. These experiments raise both fundamental and applicative issues. For applicative issues: what is the typical time of foam ageing (for a polydisperse foam) in microsystems in scope of gas pocket storage in lab-on-a-chips? Experimental results show that a typical time of 2–3 mn is found, leading to the possibility of short-time storing, depending on the application. For fundamental interests, 2D foam ageing is generally described by von Neumann's law (VON NEUMANN J., Metal Interfaces (American Society of Metals, Cleveland) 1952, p. 108) which is based on the hypothesis that bubbles are separated by thin films. Does this hypothesis still hold for foams confined in a 40 m height geometry? This problematic is analyzed and it is shown that von Neumann's law still holds but that the diffusion coefficient involved in this law is modified by the confinement which imposes a curvature radius at Plateau borders. More precisely, it is shown that the liquid fraction is high on a film cross-section, in contrast with macrometric experiments where drainage occurs. An analytical description of the diffusion is developped taking into account the fact that soap film height is only a fraction of the cell height. While most of microfoams are flowing, the experimental set-up we describe leads to the achievement of a motionless confined microfoam.
47.57.Bc - Foams and emulsions.
66.10.C- - Diffusion and thermal diffusion.
81.40.Cd - Solid solution hardening, precipitation hardening, and dispersion hardening; aging.
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