MONTE-CARLO SIMULATION STUDIES OF ELECTROLYTE IN MIXTURE WITH A NEUTRAL COMPONENT

Monte Carlo simulations are obtained for a multicomponent primitive mo del mixture consisting of a symmetric 1:1 electrolyte and a neutral pa rticle. The equilibrium structure and thermodynamics are studied as a function of the concentration of the electrolyte and concentration of the neutral species. For the unequal-sized mixture the simulations cle arly indicate a transformation in the nature of interaction between tw o like ions from being repulsive at low concentrations of the neutral component to being attractive at higher concentrations of the neutral component. The computer results are used to assess the accuracy of the corresponding predictions from the symmetric Poisson-Boltzmann, the m odified Poisson-Boltzmann, and the hypernetted chain theories. Compari son of the pair distribution functions and thermodynamics shows that t he theoretical results are in semiquantitative or better agreement wit h the simulation results. While the good agreement of the modified Poi sson-Boltzmann and the hypernetted chain results with the Monte Carlo data is expected, the results from the relatively simple symmetric Poi sson-Boltzmann theory shows a surprisingly good overall consistency wi th the simulations. (C) 1997 American Institute of Physics.