A percolation theory of ionic clustering in electrolytes

Monte Carlo simulation of the nonadditive restricted primitive model of ionic fluids: phase diagram and clustering

We report an accurate Monte Carlo calculation of the phase diagram and clustering properties of the restricted primitive model with nonadditive hard-sphere diameters. At high density the positively nonadditive fluid shows more clustering than in the additive model and the negatively nonadditive fluid shows less clustering than in the additive model; at low density the reverse scenario appears. A negative nonadditivity tends to favor the formation of neutrally charged clusters starting from the dipole. A positive nonadditivity favors the pairing of like ions at high density. The critical point of the gas-liquid phase transition moves at higher temperatures and higher densities for a negative nonadditivity and at lower temperatures and lower densities for a positive nonadditivity. The law of corresponding states does not seem to hold strictly. Our results can be used to interpret recent experimental works on room temperature ionic liquids.

The effects of the physical cluster formation on pair-correlation functions for an ionic fluid

A system of two integral equations, which is equivalent to the Ornstein-Zernike equation, results in two kinds of correlation functions which describe the apparent effects of the physical cluster formation on pair-correlation functions. Each pair-correlation function is equivalent to the sum of the two kinds of correlation functions, and the development of physical clusters, which are formed in an ionic fluid owing to the attractive Coulomb force between positive and negative charged particles, allows the dependence of the sum on the distance r between particular pair particles to develop the deviation from the behavior characterized as r-1. Then, their development makes the dependence of the sum on r have a tendency to approach the behavior characterized as r-3/2, and the two kinds of correlation functions aid in describing fractal structures of nonuniform particle distributions in ionic fluids.

Phase diagram of charged dumbbells: a random phase approximation approach

The phase diagram of the charged hard dumbbell system (hard spheres of opposite unit charge fixed at contact) is obtained with the use of the random phase approximation (RPA). The effect of the impenetrability of charged spheres on charge-charge fluctuations is described by introduction of a modified electrostatic potential. The correlations of ions in a pair are included via a correlation function in the RPA. The coexistence curve is in good agreement with Monte Carlo simulations. The relevance of the theory to the restricted primitive model is discussed.

Percolation in ionic fluids and formation of a fractal structure

The size of a dense region in the nonuniform distribution of particles generated in an ionic fluid can develop under certain conditions, as the charge on each particle increases. To derive this result, it is assumed that such a dense region is an ensemble of particles linked to each other as particle pairs that satisfy the condition E(ij)+u(ij)(r)< or =0, where E(ij) is the relative kinetic energy for i and j particles and u(ij)(r) the Coulomb potential. The percolation of the ensemble can be estimated analytically. The result described above has been derived from this estimation. According to the pair connectedness function derived for analytic estimation of the percolation, the dense region resulting from the contribution of the Coulomb attractive force between positive and negative particles can produce a fractal structure with a fractal dimension of 1.5. Furthermore, a configuration of charged particles, which can be approximately drawn from a characteristic of the pair connectedness function, agrees with that of the Bjerrum theory.