Novel method for the estimation of the binding isotherms of ionic surfactants on oppositely charged polyelectrolytes

One of the most important characteristics of the polyelectrolyte/surfactant interaction is the binding isotherm of the surfactant because it provides basic thermodynamic information about the binding mechanism. However, the amount of the surfactant bound to the polymer may crucially affect the surface properties of these systems via changing the thermodynamic activity of the components. Therefore, a knowledge of the binding isotherms can also be useful in tuning the efficiency of commercial products. However, the determination of these isotherms is still subject to significant experimental difficulties. In this letter, we offer a novel method for the estimation of binding isotherms based on electrokinetic measurements. The technique provides a simple and quick way to estimate the bound amount of surfactant that might be useful in both fundamental and industrial research. In principle, the proposed method could also be extended to the determination of the binding isotherms of small ligands on biomacromolecules.