Electric double layer forces in the presence of polyelectrolytes

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Abstract
An electric double layer is studied by means of Monte Carlo simulations and mean‐field theory. The counterions of the uniformly charged surfaces are modeled as flexible polyelectrolytes. For this particular model system it turns out that the traditional double layer repulsion becomes attractive for a wide range of systems. The main reason for this attraction is an entropically driven bridging mechanism, and its magnitude is significant compared to ordinary double layer or van der Waals forces. The polyelectrolyte Poisson–Boltzmann theory developed here behaves in a qualitatively correct manner, also predicting an attractive interaction extending over several nanometers. These results may have some relevance to technical and biological systems, where sometimes puzzling force behavior is seen in the presence of polyelectrolytes.