Simulations of Simple Fluids and Surface Forces

Abstract: A considerable part of all chemistry in nature and in industry occurs in solvents. Sol- vents affect both the interactions and the reactions of the particles immersed in them. The work in this thesis concerns the properties of ionic and polar solvents, as well as the interactions between solutes and/or dispersed particles. Molecular simulations and simple approximate theories were used to study these systems. The objective was to rigorously compare theoretical and experimental outcomes. Dielectric properties for various polar fluids have been studied in hyperspherical geome- try, and an excellent agreement was found with other simulation techniques. Classical van der Waals forces between two spherical bodies composed of dipoles have been investigated and simulations and continuum theories are found to agree with each other even at ex- tremely small separations. The charge capacitance of room-temperature ionic liquids has also been investigated. It turns out that dispersion forces are essential to explain the experimentally observed double hump, close to zero charge, in the differential charge capacitance curve. Surface forces mediated via ions and nanoparticles have been studied, using coarse- grained models. Two oppositely charged surfaces are found to repel each other at high concentrations of asymmetric multivalent salt, due to an overcharging at one of the sur- faces. Charged nanoparticles are found to be effective stabilizers for colloidal microparticles. The nanoparticles adsorb on oppositely charged surfaces due to direct Coulombic attrac- tion, but can also adsorb on like-charged microparticles via a charge regulation mechanism. Long-range attractions are found when the microparticles are neutralized with adsorbed nanoparticles, with the strength of the attraction depending on the charge of the nanopar- ticles. All these findings are in excellent agreement with experiments.