Stratification of foam films made from polyelectrolyte solutions

Studies of thin liquid films, made from semidilute polyelectrolyte solutions, are presented. The disjoining pressure variation with film thickness exhibits oscillations, corresponding to film stratification. The oscillations become sharper as the polymer concentration $c$ increases, and disappear when salt is added. The period of the oscillations scales as $c^{-1/2}$. The observed stratification is related to the polymer network and the size of the steps to the mesh size $\xi$