Monte Carlo study of the capacitance of the double layer in a model molten salt

Abstract

Monte Carlo simulations are reported for charged hard spheres at high density near a charged wall. This system is a simple model for a molten salt double layer. Unfortunately, the reduced temperatures that correspond to experiment are very small. This results in a large Boltzmann factor. As a result, we are unable to obtain meaningful results for such low values and report results only for moderately low values of the reduced temperature. Even so, our results should be a useful benchmark. Further, we are able to give a qualitative answer to an interesting question. We find that at low temperatures the capacitance near the point of zero charge increases with increasing temperature. This agrees with experiment for molten salts and disagrees with the behavior of double layer in dissolved salts, which can be modeled with low density and high temperature charged hard spheres near a wall. This also disagrees with the predictions of the Gouy-Chapman theory and the mean spherical approximation. It appears that it is the approximations, and not the charged hard sphere double layer model, that are at fault for describing double layers in molten salts. © 1999 American Institute of Physics.