Electrostatic wetting transition: charge inversion and like charge attraction

The study of the Electrical Double Layer lies at the heart of soft matter physics. In the so-called weak coupling limit, mean-field Poisson Boltzmann has enjoyed significant successes, but the absence of ionic correlations does not allow it to even qualitatively explain many fundamental moderate and strong coupling phenomena such as charge inversion and like-charge attraction. Here we develop a Gaussian fluctuation theory that self-consistently includes ion-ion correlations and excluded volume effect. Our theory predicts an ionic correlation induced liquid-like boundary layer on the surface. In the intermediate salt concentration regime, this wetting transition results in charge inversion. At higher concentrations, the charge inversion disappears, and the effective charge regains its original sign. Our theoretical results are in good agreement with both experiments and simulations.
Furthermore, we show that the overlap between the condensed layers on two like-charged surfaces leads to a short-range attraction. At high salt concentrations, the condensed layer dissolves, and a reentrant repulsive force appears. Our work provides the first explanation of the resolubilization of charged colloids in agreement with the non-monotonic nature of the effective surface charge.