Europhys. Lett.
Volume 69, Number 4, February 2005
Page(s) 636 - 642
Section Interdisciplinary physics and related areas of science and technology
Published online 14 January 2005
Europhys. Lett., 69 (4), pp. 636-642 (2005)
DOI: 10.1209/epl/i2004-10374-3

From "discrete" to "continuum" flow in foams

S. Rodts1, J. C. Baudez2 and P. Coussot1

1  LMSGC (UMR113 LCPC-ENPC-CNRS), Institut Navier Champs sur Marne, France
2  Cemagref - Domaine des Palaquins, Montoldre, France

received 22 July 2004; accepted in final form 3 December 2004
published online 14 January 2005

From both NMR and conventional rheometrical data we show that a foam cannot flow steadily below a critical, apparent shear rate and a critical shear stress. At low velocities the shear localizes in a layer of thickness decreasing with the apparent shear rate. When this thickness becomes smaller than a critical value $h_{\ab{c}}$ (about 25 bubble diameters) the continuum assumption is no longer valid and the apparent behavior in this "discrete" regime differs from the rheological behavior of the foam in the "continuum" regime (for a sheared thickness larger than $h_{\ab{c}}$).

83.80.Iz - Emulsions and foams.
83.10.Gr - Constitutive relations.
83.60.La - Viscoplasticity; yield stress.

© EDP Sciences 2005