In the paper force measurements are presented at freestanding films made from aqueous solutions of polyelectrolyte/surfactant mixtures or amphiphilic charged diblock-copolymers. Above a certain polymer concentration both kinds of films show stepwise thinning after increasing the outer pressure. But the reasons for the stratification are assumed to be different. In the case of polyelectrolyte/surfactant films the step size is similar to the correlation length found in the respective bulk solution by SANS. The step size depends on the used polyelectrolyte and is independent of the surfactant. Therefore it is concluded that the same interactions between the chains are responsible for the mesoscopic structuring of the polyelectrolytes in the bulk solution and for the ordering of the chains trapped between two film interfaces. In the films of diblock copolymers the polyelectrolytes are grafted at the film interface and form a kind of brush. The step size corresponds to the diameter of a diblock copolymer micelle and it is assumed that one layer of micelles can be trapped in the film at low outer pressure.
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Regine von Klitzing (2000) studied this question.