The structure of electrolytes at charged surfaces: The primitive model

The effects of ion size on the structure of a primitive model electrical double layer at a charged surface is considered using the integral equation method based on a combined hypernetted chain and mean spherical approximation (HNC/MSA). The HNC/MSA is shown to be a nonlinear weak field approximation. The contact values of the surface ion distribution functions are shown to have the correct quadratic dependence on the surface charge density, An analytical comparison between the HNC/MSA and earlier work based on the modified Poisson–Boltzmann equation is given.