A Monte Carlo simulation and symmetric Poisson-Boltzmann study of a four-component electrolyte mixture

The structure and thermodynamics of a four-component electrolyte mixture co nsisting of two electrolytes with a common ion, and a neutral species are s tudied using the canonical Metropolis Monte Carlo simulations. The steric e ffects of the neutral species are seen to shape substantially the equilibri um fluid properties, an important result being the existence of an attracti ve force between like-charged ions at sufficiently high concentrations of t he neutral species. Parallel calculations performed utilizing a symmetric P oisson-Boltzmann theory reveal the usefulness of the classical theory; it i s able to predict (a) the simulation profiles and the thermodynamics to a v ery reasonable degree of accuracy up to moderate solution concentrations, a nd (b) the attractive interaction between like-charge ions under the influe nce of high contents of neutral particles. These are useful results since t he generalizations of the more formal statistical mechanical theories to fo ur or more components require very extensive numerical work. (C) 1999 Ameri can Institute of Physics. [S0021-9606(99)50436-4].