Structural Forces in Thin Films Made from Polyelectrolyte Solutions

Abstract

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 ${c}^{\ensuremath{-}1/2}$. We propose that the observed stratification is related to the polymer network and the size of the steps to the mesh size $\ensuremath{\xi}$.