Myroslav Holovko

On the influence of ionic association on the capacitance of an electrical double layer

The concept of ionic association is applied to give an explanation of the anomalous temperature dependence of the capacitance of the electrical double layer. It is shown that, except in the intermediate region where the temperature derivative of the capacitance changes sign, a Bjerrum-like correction of the mean spherical approximation, with Ebelings expression for the association constant, satisfactorily reproduces the computer simulation data at high and low temperatures. Including polarization effects that arise from ionic pairs improves the description in this region.

A comparison of density functional and integral equation theories vs Monte Carlo simulations for hard sphere associating fluids near a hard wall

We make a comparison of a perturbation density functional (DF) theory and an integral equation (IE) theory with the results from Monte Carlo simulations for nonuniform fluids of hard spheres with one or two association sites. The DF used applies the weighting from Tarazona’s hard sphere density functional theory to Wertheim’s bulk first order perturbation theory. The IE theory is the associative form of the Henderson–Abraham–Barker (HAB) equation. We compare results from the theories with simulation results for density profiles and adsorption of one- and two-sited associating fluids against a hard, smooth wall over a range of temperatures and molecular densities. We also report fraction of monomers profiles for the DF theory and compare these against simulation results. For dimerizing fluids, the DF theory is more accurate very close to the wall, especially at higher densities, while the IE theory has more accurate peak heights and positions away from the wall, also especially at higher densities. Accurac...

Ionic Soft Matter: Modern Trends in Theory and Applications

Dedication.- Preface.- Field theoretical approach for ionic systems D. di Caprio, J. Stafiej.- Induced charge computation method D. Boda et al.- Concept of ion association in the theory of electrolyte solutions M. Holovko.- Towards the role of the range of intermolecular interactions I. Nezbeda , J. Kolafa.- Collective dynamics in ionic fluids I. Mryglod et al.- Criticality of ionic liquids in solution W. Schroer.- Liquid/vapor criticality in Coulombic and related fluids P.J. Camp et al.- Macroions in solution V. Vlachy et al.- Anomalous small-angle X-ray scattering in rod-like polyelectrolytes M. Ballauff.- Macroions under confinement A.D. Trokhymchuk.- Grain interaction and ordering in a dusty plasmas O. Bystrenko.- Dipolar fluid inclusions in charged matrices M.J. Fernaud, E. Lomba .- Solute ions at ice/water interface A.D.J. Haymet et al.- Proton transport in polymer electrolyte fuel cell membranes E. Spohr.- DNA saline solutions near surfaces B.M. Pettit.- Charge transport in highly-radioactive substance O. Zhydkov.- Participants.- Index.-

Network forming fluids: Integral equations and Monte Carlo simulations

A network forming four-site model associative fluid (with freely located sites) is investigated by means of associative Ornstein–Zernike integral equation theory supplemented by a Percus–Yevick-like closure relation. Since the model exhibits critical behavior, the structure relevant to the gaseous and to the liquid phases are discussed. The properties of network forming systems with different strengths of the site-site attraction are analyzed. This allows us to describe topologically asymmetrical network clusters and branching polymers. It is determined that the critical temperature as well as the critical density become lower with an increasing degree of asymmetry. NVT Monte Carlo simulations for the same model, but with a fixed location of sites, are presented. Theoretical predictions are compared to the simulation results. It is shown that the theory agrees well with the simulations, except for low densities and temperatures, where the simulations predict a well developed waterlike structure with a tet...

ASSOCIATIVE REPLICA ORNSTEIN-ZERNIKE EQUATIONS AND THE STRUCTURE OF CHEMICALLY REACTING FLUIDS IN POROUS MEDIA

A model for a chemically associating fluid, adsorbed in a disordered porous media, is proposed. The formation of the associates occurs through the directional bonding between the fluid particles. For simplicity, we restrict our attention to the dimerization of particles. In the absence of association, this model reduces to that of Kaminsky and Monson (KM) for the adsorption of methane in a xerosilica gel. This model is studied by means of the replica Ornstein–Zernike ROZ equations, with the hypernetted chain approximation, extended for associating fluids. It follows from a comparison with the computer simulation data that this theory yields a very good description of the structural properties of the KM model. The influence of the fluid density, the matrix packing fraction, and the association energy on the dimerization in the disordered matrix is studied. The fluid compressibility for the KM model and for the dimerizing fluid in a disordered matrix is obtained via the compressibility equation.

The role of ion-aggregate formation in the calculation of physical properties of electrolyte solutions

Abstract The use of chemical models is shown based on pair distribution functions (pdf) taking into account long and short-range interaction forces on the McMillan–Mayer (MM) level for the calculation of thermodynamic properties (association constant, activity coefficient, osmotic coefficient) and transport properties (conductivity) of electrolyte solutions from dilute to concentrated solutions. Extensions of the Debye–Huckel theory including ion association and solvation are used at low concentrations. High concentrations are treated by the use of the mean spherical approximation (MSA), the MSA–mass action law (MAL), and the associative MSA (AMSA) permitting one the access to systems with ion aggregation to trimers and tetramers. Comparison is made with experimental data.

Static dielectric properties of a flexible water model

The linear response theory is applied to the interaction site model for the evaluation of static dielectric properties of a flexible water model. The atom–atom radial distribution functions derived from hybridization of the computer simulations and optimized cluster theory [A. D. Trokhymchuk, M. F. Holovko, E. Spohr, and K. Heinzinger, Mol. Phys. 77, 903 (1992)] are employed for the calculation of the polarization structure factor and the moments of the polarization correlation function. The color charge version of the dipolar hard sphere model [F. O. Raineri, H. Resat, and H. L. Friedman, J. Chem. Phys. 96, 3068 (1992)] proved to be helpful for the understanding of the effects of intramolecular charge distribution and flexibility on the dielectric properties of the interaction site model. The dielectric constant for the flexible BJH water model is calculated and the region of negative values of the static dielectric function is obtained. The possibility of a subdivision of this region into two parts at k...

Contact conditions for the charge in the theory of the electrical double layer

In this paper, from the Born-Green-Yvon equations of the liquid-state theory, we derive a general expression for the charge-density contact value at charged interfaces. This relation is discussed, in particular, for symmetrical electrolytes. We emphasize an essential coupling between the electric properties and the density profile. Limiting behavior at small and large charges at the interface is discussed.

A solution of the multiple-binding mean spherical approximation for ionic mixtures

The mean spherical approximation (MSA) for an arbitrary mixture of charged hard spheres with saturating bonds is solved in the Wertheim formalism. Any number of bonds is allowed. It is shown that the general solution is given in terms of a screening MSA-like parameterΓT, a cross-interaction parameterηβ that will depend on the binding association equations, the set of binding association fractions, and an additional algebraic equation. The equation forΓT is given for the general case. The equation forηβ, however, depends strongly on the particular closure that is used to compute the contact pair correlation function. The full solution requires, as in the dimer case recently solved by Blum and Bernard, solvingm+2 equations and additionally the inversion of a matrix of size [(ν−1)m] for a system withm components and ν bonds. We recall that when ν=1, only dimers are allowed; for ν=2, only linear chains are formed: and when ν≥3, branching of the polymers occurs. It can be shown that the excess entropy for the polymer case is as before,ΔSMSA=(ΓT)3/3π + sticky terms, where the sticky terms depend on the model and will be given in future work.

Continuum Percolation of the Four-Bonding-Site Associating Fluids

Wertheim’s integral equation theory for associating fluids is reformulated for the study of the connectedness properties of associating hard spheres with four bonding sites. The association interaction is described as a square-well saturable attraction between these sites. The connectedness version of the Ornstein-Zernike (OZ) integral equation is supplemented by the PY-like closure relation and solved analytically within an ideal network approximation in which the network is represented as resulting from the crossing of ideal polymer chains. The pair connectedness functions and the mean cluster size are calculated and discussed. The condition for the percolation transition and the analytical form of the percolation threshold are derived. The connection of the percolation with the gas-liquid phase transition is discussed.