Relation between oxidation kinetics and reactant transport in an aqueous foam.

We find experimentally that the mass of dissolved copper presents a maximum with the drainage flow rate, and thus with the foam liquid fraction. Modeling analytically the transfer of H and O through the foams enables us to show that this non-monotonic behavior results from a competition between the advective flux of H ions and the unsteady diffusion of O through the thin liquid films which tends to be slower as the area of the thin liquid films decreases with the drainage flow rate and the liquid fraction. This study shows for the first time how to optimize the foam structure and drainage flow in reactive foams in which the reactants are present both in the liquid and gaseous phases.