From "discrete" to "continuum" flow in foams

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When this thickness becomes smaller than a critical value h(c) (about 25 bubble diameters) the continuum assumption is no longer valid and the apparent behavior in this "discrete" regime differs from the rheological behavior of the foam in the "continuum" regime (for a sheared thickness larger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(c)).