We present a new and computationally efficient methodology using osmotic ensemble Monte Carlo (OEMC) simulation to calculate chemical potential-concentration curves and the solubility of aqueous electrolytes. The method avoids calculations for the solid phase, incorporating readily available data from thermochemical tables that are based on well-defined reference states. It performs simulations of the aqueous solution at a fixed number of water molecules, pressure, temperature, and specified overall electrolyte chemical potential. Insertion/deletion of ions to/from the system is implemented using fractional ions, which are coupled to the system via a coupling parameter λ that varies between 0 (no interaction between the fractional ions and the other particles in the system) and 1 (full interaction between the fractional ions and the other particles of the system). Transitions between λ-states are accepted with a probability following from the osmotic ensemble partition function. Biasing weights associated with the λ-states are used in order to efficiently realize transitions between them; these are determined by means of the Wang-Landau method. We also propose a novel scaling procedure for λ, which can be used for both nonpolarizable and polarizable models of aqueous electrolyte systems. The approach is readily extended to involve other solvents, multiple electrolytes, and species complexation reactions. The method is illustrated for NaCl, using SPC/E water and several force field models for NaCl from the literature, and the results are compared with experiment at ambient conditions. Good agreement is obtained for the chemical potential-concentration curve and the solubility prediction is reasonable. Future improvements to the predictions will require improved force field models.

A theoretically based closed-form analytical equation for the radial distribution function, g(r), of a fluid of hard spheres is presented and used to obtain an accurate analytic representation. The method makes use of an analytic expression for the short- and long-range behaviors of g(r), both obtained from the Percus-Yevick equation, in combination with the thermodynamic consistency constraint. Physical arguments then leave only three parameters in the equation of g(r) that are to be solved numerically, whereas all remaining ones are taken from the analytical solution of the Percus-Yevick equation.

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Monte Carlo and molecular dynamics simulations on pure water and aqueous electrolyte solutions exposed to a strong external electric field were used to model the electrospinning process from the free liquid surface, with the goal of assessing their potential to gain insight into the molecular-level mechanisms underlying the process. Three regimes involved in the electrospinning processthe free liquid surface, the apex of the Taylor cone, and the erupting jetwere selected for simulation using three different strategies. All simulations provide the same qualitative picture and exhibit scenarios consistent with experimental observations. It is found that ions play only a rather secondary role, in the sense that the process is driven by the water molecules. The strong electric field near the tip of the Taylor cone initially arranges the water molecules, creating an embryo of a jet into which the ions subsequently enter. At high concentrations, the ions can destabilize the jet, leading to electrospraying. At low electrolyte concentration, the embryo grows, leading to a stable jet and potentially to generation of a meso-/macroscopic fiber.