Monte Carlo simulations of a mixture of an asymmetric electrolyte and a neutral species

The equilibrium properties of a charge and size asymmetric, multicomponent mixture of macroions, counterions, and neutral particles are characterized through Monte Carlo simulations. Particular emphasis is paid to considering the influence on these properties of macroion concentration, neutral component concentration, macroion charge, and counterion charge. A significant result of the simulations is that sufficient increase in the neutral species concentration leads to a gradual change in the qualitative nature of the interaction between two macro-ions from repulsive to attractive. This occurs for all the counterion charges, macroion charges, and macroion concentrations. Overall, the structure and thermodynamics are shaped by the collective and often competing effects of the species. The simulations are supplemented by theoretical calculations using the symmetric Poisson-Boltzmann, the modified Poisson-Boltzmann, and the hypernetted chain approaches. The theories show reasonable consistency, both among themselves and with the simulations, overall, although the level of agreement with the simulations varies.