Surface interactions in simple electrolytes

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Abstract
We present some new results and concepts which have emerged from the rigorous application of the integral equation methods of liquid state physics to the problem of inhomogeneous ionic fluids in the vicinity of charged surfaces. The report summarizes our recent results for surface interactions in mono- and divalent electrolytes obtained using the anisotropic Hypemetted Chain approximation. Compared to the Poisson-Boltzmann mean-field theory the major differences are an attractive contribution to the surface interaction due to ion-ion correlations and a repulsion from the ionic cores. The attraction is particularly strong in divalent electrolytes, where the double-layer repulsion is dramatically weakened or turned into an attraction. Some consequences of this pressure contribution and its connection to Van der Waals interactions are pointed out. The size of the ions affects the pressure predominantly at short surface separations, and then to a substantial extent for large ion radii or at high surface charge