A phenomenological description of the anomalous behavior of the electrical double layer at low temperatures

A simple description that accounts for some recent simulations of the electric double layer of a charged hard sphere fluid that show anomalously large negative adsorption of the ions at a surface and an unusual positive temperature derivative for the capacitance at low temperatures is discussed. The treatment is phenomenological since it does not result from any controlled approximation but it is reasonably well founded. The mean spherical approximation expressions for the density profiles of this system, which do not exhibit anomalous behavior, are modified in light of an exact contact value condition, the Ornstein-Zernike theory of the critical point, and some plausible reasoning. The agreement with the simulation results is fairly good. At the moment, there is no theory that accounts for these recent simulation results. (C) 2000 American Institute of Physics. [S0021- 9606(00)51815-7].