Time evolution of aqueous foams: drainage and coarsening

We report new results on drainage and coarsening of aqueous foams. We show that these two effects can strongly interfere, enhancing the drainage velocity. Without coarsening, we have performed free-drainage experiments, in which local drainage rates are measured by electrical conductivity and by light scattering techniques. We have investigated the roles of the bubble size, of the surface and bulk rheology and of the liquid fraction. The results show that changing these foam parameters can induce transitions between different drainage regimes. The results are analysed in terms of two dimensionless numbers describing the balance between surface and bulk dissipation. 1