We have studied thin liquid films made from semidilute polyelectrolyte solutions. The disjoining pressure (due to interaction between film surfaces) has been measured as a function of the film thickness. We observe pressure 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 $c^{-1/2\mathrm{}}$. We propose that the observed stratification is related to the polymer network and the size of the steps to the mesh size $\xi$.

• Received 5 March 1997

DOI:https://doi.org/10.1103/PhysRevLett.78.4974