Polymer-mediated interactions of fluid membranes in a lyotropic lamellar phase: a small angle X-ray and neutron scattering study

Small angle X-ray and neutron scattering data on an effective three-component lamellar phase composed of water, a non adsorbing water-soluble polymer (polyvynilpyrolidone), fluid membranes, made from a mixture of a cationic surfactant (cetylpiridiumchloride) and a cosurfactant (hexanol), are presented for various membrane as well as polymer concentrations. The data are fitted with a recently proposed model which takes into account the geometry and the fluctuations of these periodic structures. This allows a quantitative study of the polymer contribution to the smectic compression modulus (B) over bar of the lamellar phase, Four different regimes of polymer confinement are expected. The associated variations in (B) over bar are compared to a recent theoretical model, which predicts the polymer-mediated contribution to the smectic compression modulus.