Monte Carlo simulations of complex fluid mixtures with multibody electrostatic interactions

The molecular simulation of complex fluids is important in research areas such as biology, colloidal science, separation processes, geology, and electrochemistry. Complex fluids consist of polar or ionic species and their mixtures, which interact through long-range intermolecular forces. Simulation studies are advantageous in that they can be performed under conditions that are unattainable in the laboratory, can involve species that are expensive or hazardous, and can probe properties which experiments cannot measure directly.; In this thesis, the effect of implementing phenomenological electrostatic interactions in binary fluid mixtures is investigated. One phenomenon is the multibody interaction between molecules due to electrostatic polarization. The second is di-electric saturation in the vicinity of a solvated ion. First, the effect of polarization on the phase diagrams for a mixture of a dipolar solvent and a polarizable solute was analyzed. Few simulation studies have been performed to determine systematically the effect of polarization on thermodynamic properties. By tuning the polarizability of the solute, the effect of polarization on the coexistence properties of the system was quantified. This approach was also applied to a methanol-methane mixture, producing better agreement with experiment in the vapor phase.; A second study consisted of direct simulation of the critical loci of binary fluid mixtures. The effect of polarization of methane, introduced via fluctuating charges, was investigated for the water-methane mixture near the critical point of water. Quantitative results were obtained for a methane-ethane system, which was used to test the methodology. Qualitative behavior was predicted for the water-methane mixture, but results depend on the intermolecular potentials and combining rules for the interaction between different species.; Finally, implicit-water potentials for the simulation of 1:1 electrolyte solutions of LiCl, NaCl, and KCl at 298 K, the temperature associated with biological function, were developed. Two short-range corrections were made to the interionic potential to account for dielectric saturation in the vicinity of the ion and repulsion due to hydration. With the addition of these corrections, both structural and thermodynamic properties, measured by the radial distribution function and the mean ionic activity coefficients were reproduced more accurately.