Static properties of a dendrimer with generation g = 5 with positively charged terminal groups in an athermal solvent are studied by lattice Monte Carlo simulations using the cooperative motion algorithm as the tossing scheme. The calculations are performed both for a salt-free system with neutralizing counterions and for a small amount of added monovalent and divalent salt. The full Coulomb potential and the excluded volume interactions between ions and beads are taken explicitly into account with the reduced temperature tau, the number of salt cations (anions) n(s), and salt valence z(s) as the simulation parameters. The bahaviour of the systems is analyzed by the mean effective charge per end-bead , Coulomb mean energy , mean-square radius of gyration , pair correlation functions g(alphabeta), and charge density rho(ch). The simulations show that for n(s)> or = 0 and decreasing tau: (a) there is encapsulation in the dendrimer and condensation onto the terminal groups of anions accompanied by a monotonic decrease in and and by subsequent swelling and shrinking of the molecule; (b) encapsulation, condensation and shrinking are the most significant and swelling weaker for |z(s)| = 2; (c) penetration of salt cations into the dendrimer is minor when compared to that of anions; (d) rho(ch) is reduced and becomes negative close to the center of mass of the dendrimer and on its periphery; (e) for the considered n(s) > 0, unlike divalent salt ions the monovalent ones cause slight effects when compared to the salt-free case.

Results of the Monte Carlo simulation of the electrode/molten salt interface are reported. The system investigated was modeled by the restricted primitive model of electrolyte being in contact with the charged hard wall (hard spheres of diameter d=400 pm and relative permittivity epsilon(r)=10). The temperature analysis of the mean activity coefficient gamma(+/-), heat capacity C(v) and radial distribution function, g, indicated the range of temperatures of the study. Calculations for the electrode/electrolyte interface were carried out for temperatures 1300, 1400, and 1500 K and in the range of the electrode charge densities sigma from 0.025 to 0.5 C m(-2). Singlet distribution functions showed a multilayer structure of the electrolyte in the vicinity of the electrode surface. The structure depended on the electrode charge, but not much on temperature. The capacitance curves had a parabolalike shape with the maximum located at sigma=0. This result is not consistent with the Gouy-Chapman theory, but has been confirmed by the modified Poisson-Boltzmann theory, which includes the correlation and exclusion volume effects.

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Results of the Monte Carlo simulation of the electrode | molten salt interface are reported. The system investigated is represented by a primitive model of electrolyte in contact with a planar charged hard wall. The density of an electrolyte is comparable with the density of real molten salts. The calculations are performed for T = 1500 K, which is above the phase transition temperature determined from Monte Carlo analysis of the heat capacity C V and the radial distribution function. The density and charge profiles reveal a multilayer structure of the electrolyte in the vicinity of the electrode surface. The differential capacitance has a distorted camel-shape similar to that predicted by theory and observed for some ionic liquids.

The spatial extension of the ionic cloud neutralizing a charged colloid or an electrode is usually characterized by the Debye length associated with the supporting charged fluid in the bulk. This spatial length arises naturally in the linear Poisson-Boltzmann theory of point charges, which is the cornerstone of the widely used Derjaguin-Landau-Verwey-Overbeek formalism describing the colloidal stability of electrified macroparticles. By definition, the Debye length is independent of important physical features of charged solutions such as the colloidal charge, electrostatic ion correlations, ionic excluded volume effects, or specific short-range interactions, just to mention a few. In order to include consistently these features to describe more accurately the thickness of the electrical double layer of an inhomogeneous charged fluid in planar geometry, we propose here the use of the capacitive compactness concept as a generalization of the compactness of the spherical electrical double layer around a small macroion (González-Tovar et al., J. Chem. Phys. 2004, 120, 9782). To exemplify the usefulness of the capacitive compactness to characterize strongly coupled charged fluids in external electric fields, we use integral equations theory and Monte Carlo simulations to analyze the electrical properties of a model molten salt near a planar electrode. In particular, we study the electrode's charge neutralization, and the maximum inversion of the net charge per unit area of the electrode-molten salt system as a function of the ionic concentration, and the electrode's charge. The behaviour of the associated capacitive compactness is interpreted in terms of the charge neutralization capacity of the highly correlated charged fluid, which evidences a shrinking/expansion of the electrical double layer at a microscopic level. The capacitive compactness and its first two derivatives are expressed in terms of experimentally measurable macroscopic properties such as the differential and integral capacity, the electrode's surface charge density, and the mean electrostatic potential at the electrode's surface.