Marginal regeneration and the Marangoni effect

On the basis of experimental observations described earlier, we have propos ed that marginal regeneration is caused by surface tension gradients at the borders of mobile foam films, Marginal regeneration is the rate-determinin g mechanism in the drainage of such films, and, as such, a determining fact or in the persistence (or long-term stability) of foams. Marangoni flows ar e caused by surface tension gradients, and these set off the exchange of th icker for thin film elements along the borders, while the total film area r emains the same. In this paper we present simulations of the drainage of Li quid in a vertical soap film, and show that it is realistic to expect large surface tension gradients along the lower border of the film under the con ditions which lead to marginal regeneration, (C) 1999 Academic Press.