Oscillatory forces from polyelectrolyte solutions confined in thin liquid films

Several combinations of polyelectrolyte-surfactant mixtures are studied to probe the various structure-property relationships these systems produce in thin liquid foam films. We show that either bulk solution properties or su rface specific adsorption of the polymer-surfactant complexes formed can do minate the thin-film behavior. Above the polymer overlap concentration, C-p *, oscillatory force profiles are observed. In agreement with previous stud ies, we find that the oscillation period, Deltah, scales as the negative sq uare root of the polymer concentration, Deltah similar to C-p(-1/2). In add ition, by comparing directly the bulk polymer correlation length, to the os cillation period, we establish for the first time that Deltah = xi for thes e systems. These findings are compared to oscillatory force behavior seen w ith micellar solutions which display a scaling relation with micelle concen tration, C-m, which follows Deltah similar to C-m(-1/3). The different scal ing exponents are explained by the local cylindrical and spherical symmetry of the molecular structures seen in the corresponding systems. Finally, it is also shown that the adsorption of polymer and/or complexes to the inter face can govern the thin-film properties and swamp out the influence of bul k structural effects in certain systems.