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We consider application to the hard sphere (HS) model of the mapped-averaging framework for generating alternative ensemble averages for thermodynamic properties. Specifically, we develop a...

We present the results of molecular dynamic studies of collective dynamics in a system of hard disks confined to a narrow quasi-one-dimensional (quasi-1D) channel. The computer simulations have been performed for the specific channel width of 3/2 of disk diameter in which the disk arrangement at close packing resembles zigzag ordering characteristic of a vertically oriented two-dimensional (2D) triangular lattice. In such a quasi-1D system, which is intermediate between 1D and 2D arrays of hard disks, the transverse excitations obey very specific dispersion law typical of the usual optical transverse modes. This is in a sharp contrast both to the 1D case, where transverse excitations are not possible, and to the 2D case, where the regular shear waves with a propagation gap were observed. Other peculiarities of the dispersion of collective excitations as well as some results of disk structuring and thermodynamics of the quasi-1D hard disk system are presented and discussed for a range of hard disk densities typical for fluid and distorted crystal states.

This article based on the archival documents and scientific periodicals, for the first time reveals a discoverer of so called transitional phase of the substance from the solid state to liquid – the liquid crystals. This fundamental discovery has been made by the Austrian scientist Julius Planer at the Lviv University in 1861.

Microscopic equations for the coefficients of the effective Landau-Ginzburg-Wilson (LGW) fluid Hamiltonian are presented in the case of the reference system that consists of hard spheres with a short-range Yukawa attraction. The mean-field level analysis of the critical parameters of the Sutherland fluid, based on the effective LGW fluid Hamiltonian with two different reference systems, namely, widely used pure hard spheres and hard spheres with the short-range Yukawa attraction, is performed. From the comparison with computer simulation data, the superiority of the reference system that incorporates the short-range attraction is shown.

Analytical solution of the first-order Ornstein–Zernike equation known as the first-order mean spherical approximation (FMSA) theory due to Tang and Lu [J. Chem. Phys. 99, 9828 (1993)] is used to write down a closed equation for the static structure factor of the hard-sphere fluid with a short-range Yukawa attraction. Calculations are performed for a Yukawa decay exponent that corresponds to a range of attraction that does not exceed the first coordination shell of Lennard-Jones-like simple fluids. By comparison with Monte Carlo simulation data it is shown that the analytical FMSA equation for the static structure factor is of the same or even of superior accuracy as that within the seminumerical mean spherical approximation theory.

This article summarizes recent theoretical research concerned understanding depletion forces. These forces appear when small colloidal particles, polymers or other entities, usually called depletants, are driven out from the gap or film between two macroparticles. Applying the modern tools of statistical mechanics and in agreement with experimental measurements it is shown that depletion attraction is only a part of more general medium-mediated interaction forces in colloidal dispersions known as structural forces. Finally, it highlights the important role that long-range structural forces could play in various applications relying on effecting particle dispersion, foam and emulsion stability, as well as wetting behavior of colloidal fluids on solid.

Collective excitations in hard-sphere fluids were studied in a wide range of wave numbers and packing fractions η by means of molecular dynamics simulations. We report the observation of non-hydrodynamic transverse excitations for packing fractions η≥0.395 in the shape of transverse current spectral functions. Dispersion of longitudinal excitations in the whole range of packing fractions shows a negative deviation from the linear hydrodynamic law with increasing wave numbers even for dense hard-sphere fluids where the transverse excitations were observed. These results do not support a recent proposal within the "Frenkel line" approach that the positive sound dispersion in liquids is defined by transverse excitations. We report calculations of the cutoff "Frenkel frequencies" for transverse excitations in hard-sphere fluids and discuss their consistency with the estimated dispersions of shear waves.

Performance of the SAFT-VR equation of state developed for the hard sphere based simple fluids, namely the square-well, Sutherland and Yukawa fluids, is examined by comparing its results with simulation data and an augmented van der Waals (vdW) equation based on a Yukawa (Y) reference. Its shown that both for the equilibrium vapor–liquid data and data along selected isotherms in the liquid and supercritical fluid phases the vdW(Y) equation provides better results, particularly when going to lower temperatures.

The vapour–liquid phase diagram of long-range Yukawa fluids with the decay parameter zσ ≤ 1 is calculated by means of an augmented van der Waals theory based on the reference system that includes both the repulsive and short-range attractive interaction. Comparison with Monte Carlo simulation data, as well as with the traditional van der Waals approach based on a purely repulsive hard-sphere reference system and other semi-analytical theoretical approaches, is made.

A novel approach to perturbed equations of state for simple fluids is presented and its advantages over the traditional perturbed hard sphere equations are demonstrated by its application to several model fluids. The approach is based on a short range Yukawa reference which incorporates, in addition to repulsive interactions, also attractive interactions at short separations. The considered models of common interest are the Sutherland, Lennard-Jones, and EXP6 fluids. It is shown that using the proposed approach the reference system captures a good deal of properties of the studied fluids and that an accurate equation of state can be obtained using only the crude mean field (augmented van der Waals) approach.

In this study, we show that the inclusion of a short-range part of the total attractive interaction into a reference system allows a natural extension of the traditional first-order perturbation theory of simple fluids to practically all thermodynamic states. This theory is applied to the thermodynamic functions and the liquid–vapor coexistence curve of the Lennard-Jones-like medium range Yukawa fluid and to the Sutherland fluid. Comparison with computer simulation data and the second-order Barker–Henderson perturbation theory is discussed.

A product−reactant Ornstein−Zernike (PROZA) extension of the Wertheim's multidensity integral equation theory techniques is applied to evaluate the structuring of the PDMS polymer melt in the bulk and in the presence of a single and a pair of silica surfaces. By comparing with simulation data, we find that the PROZA theory is not very accurate in reproducing the details of the total (the sum of intramolecular and intermolecular correlations) atom−atom radial distribution function of the united atom PDMS model. At the same time, the inhomogeneous calculations based on the PROZA theory are qualitatively correct in describing the local density distribution of the silicon atoms and a single methyl group near silica surfaces. Relating the flat surface geometry to the spherical geometry by means of the Derjaguin approximation, the results obtained for the two-surface system are used to discuss the two-particle aggregation tendency as well as some general aspects of the origin of the reinforcement phenomenon in ...

The Henderson and Chan (HC) formulae for the contact values of the radial distribution functions (RDFs) of a highly asymmetric hard sphere mixture are reconsidered in light of a recent formula of Roth, Evans and Dietrich for the RDF of a pair of exceedingly large spheres at zero concentration in a solvent of small hard spheres. Two modifications of the HC formulae using this result give a large sphere–large sphere contact value that is considerably smaller than that of the original formulation. These new HC results are compared with the molecular dynamics simulations of Lue and Woodcock, for a diameter ratio of 1:10, supplemented by a few new results that are reported here. The new HC formulae are in much better agreement with the MD results than is the popular Boublik–Mansoori–Carnahan–Starling–Leland formula. Also, some simulation results for the RDFs as functions of separation are reported.

Analytic expressions for the Laplace transform of the interaction energy and force between two exceedingly large hard spheres at infinite dilution in a polydisperse hard-sphere suspending fluid are presented. The equations are based on the Percus–Yevick approximation for the many-component suspending fluid, supplemented by the hypernetted chain approximation for the correlation function of the suspended spheres. By applying the Derjaguin approximation, the energy and force results for two spheres are related to the energy per unit area and the disjoining pressure between two flat walls suspended in a polydisperse fluid. Numerical results for the representative Schultz distributions of the diameters of the species comprising the suspending fluid are presented and discussed.

A convenient approximation is proposed for the correlation function of a pair of large hard-sphere particles in a bidisperse or binary hard-sphere mixture. This approximation is based on the solution of the Ornstein–Zernike/Percus–Yevick integral equations for a hard-sphere mixture. From this result, we obtain the potential of mean force and interaction force for a pair of colloidal spheres in a bidisperse hard-sphere fluid.

The analytic solution of the Poisson equation for a system of two identical charges near a uniformly charged plane is used to understand the phenomenon of an attraction between a pair of charged particles next to an oppositely charged surface that has been observed recently. We found that there is no direct attractive interaction between like charges. We have shown that what is observed experimentally could be interpreted as the ‘apparent attraction’ resulting from the extra force experienced by each charge being in the non-zero plane parallel electric field due to the charged surface. This surface-induced electric field and force are directed to the center of the surface and can oppose the direct Coulomb repulsion between like charges. Both the field and force can be obtained naturally within the framework of classical electrodynamics if the effects of the finite size of a charged surface are taken into account.

The approach to treat the strong attractive interaction between fluid particles adsorbed into porous media is reported. Results are illustrated by the calculations of liquid/vapor phase diagrams for Lennard-Jones fluid in the presence of quenched disorder. Perspectives of the approach from the comparison with computer simulation data available from the literature are discussed.

The phenomenon of layering of like-charged particles (ionic surfactant micelles or other colloidal particles) between two plane-parallel film surfaces and the evolution of in-film particle structuring are studied using the canonical Monte Carlo method combined with a simulation cell containing both the bulk solution and the film region. The simulations are performed using an effective one-component fluid potential model that incorporates micelle hard-core repulsion and both the screened Coulomb electrostatic interaction and the entropic contribution due to the discrete nature of the solvent and finite size of electrolyte ions. The proposed potential model is applied to mimic the properties of surfactant micelle solutions in the bulk and under film confinement. The effects of surfactant concentration and film thickness on the in-film micellar structuring phenomenon are analyzed. The relation of obtained results to experiments on stratifying sodium dodecyl sulfate micellar films is discussed.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 141, 114903 (2014) and may be found at https://doi.org/10.1063/1.4894438. We consider the applicability of coarse-grained molecular dynamics for the simulation of defects in a nematic liquid crystal around a colloidal particle. Two types of colloids are considered, a soft colloid resembling a liquid crystal dendrimer or a similar macromolecule. In addition, a decorated colloid is used which could represent a gold nanoparticle with mesogen-modified surface. For both models we consider homeotropic and tangential anchoring. Precise control of the easy axis on the colloid's surface enables us to focus on specific planar arrangements in the case of a decorated colloid. The nematic phase is modelled explicitly via soft spherocylinders interacting through a potential, suggested by Lintuvuori and Wilson [J. Chem. Phys. 128, 044906 (2008)]. Properties of the nematic phase are studied by computing the Frank elastic constants. In addition, estimates for the nematic-isotropic transition and the coherence length allow us to establish a relation between energy and length scales with respect to experimental systems. Both models exhibit similar defect topologies, namely, that of a Saturn ring and a boojum-type of defect for homeotropic and tangential surface anchoring, respectively. In the decorated colloid model we tune the anchoring strength through the density of the mesogenic shell on the surface. We also found the biaxial boojum defect for the special case of longitudinal planar anchoring. The study demonstrates the potential of coarse-grained simulation methods for studying defects in liquid crystals.

Canonical ensemble molecular dynamics and Monte Carlo simulations have been performed to study the vapor/liquid coexistence in a hard-core fluid with an attractive Yukawa interaction. Coexisting densities and pressure along the vapor/liquid coexistence line for different ranges of attractive interaction have been evaluated and found to agree well with the Gibbs ensemble Monte Carlo data reported in the literature. To obtain surface tension, the normal and tangential components of the pressure tensor have been calculated during simulations by using a hybrid molecular dynamics algorithm (which combines the hard-core and continuous forces) and by using an original numerical algorithm for the hard-core contribution to the virial in Monte Carlo simulations. We found that surface tension is strongly dependent on the range of attractive interaction, i.e., it drops when the attraction becomes short-ranged. The relation of the attractive hard-core Yukawa potential to the spherically-truncated Lennard-Jones potenti...

The molecular dynamics (MD) simulations and replica integral equation theory are employed for the study of the structure and dynamical properties of Kaminsky-Monson molecular model of Lennard-Jones fluid in contact with an adsorbing porous medium. Both theory and MD simulations predict quite similar results for the radial distributions of the fluid-fluid and fluid-matrix correlations which agree well with the Monte Carlo data already reported in the papers. The mean-square displacement and the velocity autocorrelation functions of fluid particles are calculated from the MD simulations and are used to analyze their self-diffusion coefficients. It is shown that the presence of porous media reduces the mobility of fluid particles and hence decreases the self-difussion coefficient.

The structure of a starlike molecule (SLM) fluid with four arms of different length is studied by applying the associative Percus–Yevick integral equation (IE) theory and canonical Monte Carlo (MC) simulations. In the IE study the SLM fluid is modelled by a fluid of hard spheres with four associative sites on each sphere while the MC has been performed for a freely-joined tangent hard sphere fluid. The total radial distribution functions have been calculated in both approaches for different volume fraction regimes and different arm lengths. It is shown that the associative IE theory predicts the structure of SLM fluid best for relatively long arms and at high densities. Additionally, the dependence of the SLM centre–centre correlations on the functionality and fluid particle density has been analysed using the MC results.

Canonical molecular dynamics (MD) and Monte Carlo (MC) simulations for liquid/vapor equilibrium in truncated Lennard-Jones fluid have been carried out. Different results for coexistence properties (orthobaric densities, normal and tangential pressure profiles, and surface tension) have been reported in each method. These differences are attributed in literature to different set up conditions, e.g., size of simulation cell, number of particles, cut-off radius, time of simulations, etc., applied by different authors. In the present study we show that observed disagreement between simulation results is due to the fact that different authors inadvertently simulated different model fluids. The origin of the problem lies in details of truncation procedure used in simulation studies. Care has to be exercised in doing the comparison between both methods because in MC calculations one deals with the truncated potential, while in MD calculations one uses the truncated forces, i.e., derivative of the potential. The truncated force does not uniquely define the primordial potential. It results in MD and MC simulations being performed for different potential models. No differences in the coexistence properties obtained from MD and MC simulations are found when the same potential model is used. An additional force due to the discontinuity of the truncated potential at cut-off distance becomes crucial for inhomogeneous fluids and has to be included into the virial calculations in MC and MD, and into the computation of trajectories in MD simulations. The normal pressure profile for the truncated potential is constant through the interface and both vapor and liquid regions only when this contribution is taken into account, and ignoring it results in incorrect value of surface tension.

We have studied the structure and adsorption of a hard sphere fluid in a rigidly fixed array of permeable matrix species. The surface of each matrix particle is represented by a barrier of finite height and width, such that the entire model describes partitioning of a fluid in a set of permeable membranes. We have applied the grand canonical Monte Carlo (GCMC) simulations and replica Ornstein—Zernike (ROZ) equations for partly quenched systems complemented by the Percus—Yevick (PY) closure as our theoretical tools. The pair distribution functions of species and the adsorption isotherms are discussed dependent on the parameters of the model. It is shown that the theory provides adequate description of the behaviour of fluid species in the interior of the matrix particles, inside the barriers, and close to the interface. On the other hand, the coordination numbers for a fluid in the matrix interior and the adsorption isotherms from the ROZ-PY theory are in excellent agreement with computer simulation data.

The adsorption isotherms for diatomic fluids in disordered porous media have been obtained from grand canonical Monte Carlo computer simulation. A disordered porous medium, or matrix, is prepared by quenching an equilibrium configuration of spherical hard core molecules. In addition, canonical Monte Carlo simulations have been performed for equilibrium binary mixtures that represent counterparts of quenched-annealed systems in question. For the same chemical potential of diatomic molecules at a fixed density of matrix species, the structure and the density of the diatomic fluid in the binary mixture and in the quenched medium are very similar. This behaviour holds also for systems with attractive interactions in the region of high temperatures. Observed similarity of the structural and thermodynamic properties of the mixture and the corresponding annealed fluid-quenched matrix system permits the use of the thermodynamics of the mixture to evaluate some properties of quenched-annealed fluids. Calculations ...

The Born–Green–Yvon (BGY) equation with Fischer–Methfessel (FM) approximation is used to calculate the density profiles of the planar liquid–vapor interface of Lennard-Jones fluid in a hard-sphere disordered rigid matrix. The density profiles are compared with the results of canonical ensemble Monte Carlo simulations. Both theory and simulation show that the thickness of the interface increases in the presence of disordered media. The phase diagrams for two different matrix densities have been evaluated and compared with the predictions of mean field and optimized cluster theories. Comparison with Monte Carlo data for low matrix densities indicates that the BGY-FM theory works reasonably well. Possible extensions of the theory are also discussed.

The replica Ornstein–Zernike (ROZ) equations, supplemented by the hypernetted chain and mean spherical closures, were solved for an ionic fluid adsorbed in a disordered charged matrix. To obtain the numerical solution of the ROZ equations we performed renormalization of the initial equations. Both the matrix and adsorbed fluid were modeled as charged hard spheres in a dielectric continuum, i.e., in the so-called restricted primitive model. As a result, the pair distribution functions between fluid ions and for fluid-matrix correlations were obtained. Structural properties were studied as a function of the matrix density, the concentration of adsorbed electrolyte and for different prequenching conditions. The isothermal compressibility, excess internal energy, and the chemical potential were calculated and discussed with respect to of the model parameters. Comparison with the Monte Carlo computer simulations of Bratko and Chakraborty [J. Chem. Phys. 104, 7700 (1996)] indicates that the theory yields qualitatively correct results for the model system.

A two-dimensional model for a chemically associating fluid adsorbed in a disordered porous media has been investigated. The model is studied by means of the associative Replica Ornstein-Zernike equations, with Perens-Yevick and hypernetted chain approximations, extended for associating fluids. The effects of disordered media density and strength of association interaction on the adsorption isotherms and structural properties of adsorbed fluid are explored. To investigate the effect of association interaction on the liquid-gas phase transition, the additional out-core interparticle interaction in the form of square-well attraction is included. This term is considered in the mean field approximation. It permits us to analyze qualitative trends of the behavior of the critical density and temperature dependence on the combined effect of association and of quenched disorder in the model of dimerizing discs with square-well attraction. Our preliminary conclusion concerning this unexplored problem is that the presence of disorder and of association have opposite effect on the critical temperature. Manipulating the matrix density and bonding between particles may keep almost unaltered the critical temperature.

The pair distribution functions and the adsorption isotherms for a hard-core dimerizing fluid in disordered hard-sphere matrices have been determined using the associative extension of replica Ornstein-Zernike equations. Some grand canonical Monte Carlo simulation results for tangent hard-sphere dumbbells adsorbed in hard-sphere matrices are presented. Theoretical predictions for the structure from the solutions of integral equations with the associative hypernetted chain (HNC) and Percus-Yevick (PY) approximation agree with those from the simulations. However, the HNC closure has been found to work better than the PY one.

The replica Ornstein–Zernike (ROZ) equations for an ionic fluid adsorbed in an electroneutral, disordered matrix of ions were applied to a model where both ionic subsystems were presented as point charges interacting only via Coulomb forces. The effects of fluid (electrolyte) and matrix concentration on the screening of the ion–ion interactions in the fluid phase were investigated. The effects of the prequenching conditions were also examined. It was shown that augmenting the matrix concentration promotes attraction between equally charged ions and repulsion between ions of opposite sign. This peculiar behavior, observed first in the simulation study of Bratko and Chakraborty [J. Chem. Phys. 104, 7700 (1996)], follows straightforwardly from the ROZ equations. Moreover, we generalized the expression for the disorder averaged ion–ion potential for an arbitrary fluid concentration and prequenching conditions. In addition to these results, which are consistent with computer studies, we present some new results that have not been observed in simulations. For example, alternating ionic ordering, generated by the influence of the charged matrix was observed. This contribution can be considered as a first step toward a study of primitive model electrolytes adsorbed in disordered matrices of hard-sphere ions. The solution of this problem will be presented elsewhere.

Canonical ensemble Monte Carlo simulations and the non-uniform Percus–Yevick (NPY) equation for the local density are used to study the influence of surface mediated thirdorder interactions on the adsorption of associating hard spheres on a hard wall. A comparison of the NPY density profiles with the computer simulations data indicates that this approximation predicts the fluid structure reasonably well.

The associative replica Ornstein-Zernike equations, supplemented by the associative hypernetted chain approximation are used to describe the Smith-Nezbeda model for an associating fluid adsorbed in a disordered hard sphere matrix. These equations have been developed by combining the replica Ornstein-Zernike equations with the Wertheim theory of association in fluids. The pair distribution functions and fraction of unbonded species are calculated. Also investigated is the influence of the association on the equation of state and the chemical potential of the absorbed fluid.

Monte Carlo simulations are reported for the distribution functions, the fraction of unbonded and bonded particles, and the pressure of a chemically associating fluid of hard discs of a circularly symmetric attractive square well. Depending on the choice of the bonding length, dimers or chain molecules of different length can be formed. The dependence of the structural properties of the model on the fluid density and association energy is discussed.

The density profiles of a dimerizing fluid near a crystalline surface are investigated. The model of the bulk fluid is that proposed by Stell and Zhou, which is a generalization of Wertheim's model for dimerization. The formation of dimers results from the interaction between the intracore attractive sites. The fluid–solid interaction consists of two terms. The non-associative term is that proposed by Steele. The directional associative fluid–solid atom interaction is chosen to have a Gaussian form. This provides bonding of the bulk fluid particles with the solid atoms. The solid substrate is assumed to be the graphite basal plane. The density profiles are studied by using the associative singlet Percus–Yevick approximation. When the distance from the surface is greater than the dimer length, the effect of crystalline symmetry is not apparent. The second adlayer tends to disappear when association is present. The relative importance of various positions in the surface unit cell tends to be less when the s...

The inhomogeneous OZ equation, together with the LMBW equation for the density profile, with the bulk associating fluid taken as a reference system, is solved. Wertheim's description of the reference fluid, which provides an adequate description of chemical association far from the surface, is used. In the vicinity of the surface, the reference inhomogeneous PY closure is formulated and applied. The theory of Wertheim for bulk association is combined, for what we believe is the first time, with a pair level theory for inhomogeneous fluids. A few preliminary results for this reference approach are reported.

The charge susceptibility function of a flexible water model is investigated using the theory of the dynamical dielectric function of interaction-site model solvent developed by H. L. Friedman and his colaborators. The atom−atom pair correlation functions used as input in this approach were derived from results of molecular dynamic computer simulations. They were extended to larger separations by the use of integral equation theory techniques. It is pointed out that a more careful description of long-ranged correlations can provide new information about the nature of the collective dynamics in water.

The associative analogue of the integral equation theory developed by Madden and Glandt is applied to a model of methane adsorbed in a silica xerogel. The integral equations are solved in the assoc...

A model of localized site adsorption of a dimerizing fluid on a crystalline surface of (100) symmetry is investigated. A heterogeneously dimerizing (A + B ⇌ AB) bulk fluid, with a square well associative interaction, is described using the model of Cummings and Stell and a particle−particle reference interaction site approximation which includes a complete expression of the intramolecular structure factor. The solid atom−fluid particle nonassociative interactions are Lennard-Jones potentials. An associative square well interaction between the fluid particles and the surface atoms is included. The model is studied numerically using singlet level integral equations for density profiles. The adlayer consists of associatively and nonassociatively adsorbed monomers and dimers. Complexes of fluid particles and surfaces atoms, formed at the on-top adsorption site, the 2-fold bridging site, and the 4-fold hollow site positions are studied. The parameters which influence the structure of the adlayer are investigated.

An investigation is begun into the structure of a chemically reacting or associating hard core Yukawa fluid near a hard wall by using Monte Carlo simulations. The model of the interparticle potential is an extension of that introduced by Cummings and Stell for an overlappping hard sphere fluid. This investigation studies the changes in the structure of this chemically reacting fluid at the wall, introduced by the presence of long-range attractive forces acting between atoms. The long-range attractive forces cause a lowering of the total number of particles in the vicinity of the wall and weaken the orientational ordering of the dimers formed by the effect of the chemical interactions. Also the singlet integral equation approach is applied to calculate the density profiles. A comparison of the theoretical predictions with the Monte Carlo data indicates that, in contrast to systems without long-range attractive forces, the singlet theory is insufficient, especially when the chemical interactions increase.

Density profiles of a double square-well model of a chemically associating fluid near a hard wall are studied using integral equations and computer simulation techniques. The model of the bulk fluid is a two-component system of ‘hard’ spheres which, if of different species, are able to overlap and form dimers. This kind of transformation represents a chemical reaction between monomeric units and is generated by an interparticle interaction in the form of an intracore attractive double square well. The dimers which consist of the same species, but differ in the bonding length, are treated as isomers of the product of the reaction of dimerization. Peculiarities in the behaviour of the bulk fluid influence the density profiles and the absorption of particles at a hard wall. The effects of chemical reaction, the bulk density, and energetic characteristics of each of the attractive wells on the density profiles are investigated. The theory is compared with Monte Carlo computer simulation data.

The radial distribution functions for a central force model of water, derived from a combination of computer simulation and integral equation techniques, are used to calculate the density-density and charge-charge structure factors. These quantities are compared with neutron scattering measurements of light and heavy water. From the behaviour of the density-density and charge-charge structure factors in the thermodynamic limit of small wavenumbers, the extent of density and charge fluctuations is estimated. In particular, the density fluctuations in water are found to extend to longer distances than charge fluctuates. The relations between the charge fluctuations and the behaviour of the static dielectric function as well as some dynamical properties are discussed.

The adsorption of associating hard spheres on a hard wall by using the nonuniform Percus–Yevick equation for the local density and the pair correlation functions is studied. A comparison of the density profiles with computer simulation data indicates that this approximation predicts the fluid structure significantly better than the singlet Percus–Yevick and hypernetted chain approximations.

A model of a chemically reacting fluid in a slit-like pore is studied. The density profiles of the fluid particles inside the pore, the adsorption isotherms, and the solvation force acting between the walls of the pore are investigated within the integral equation method. The Percus-Yevick and hypernetted chain approximations for the fluid particle-pore correlations are used. The model for the bulk chemically reacting fluid is that proposed by Cummings and Stell for a mixture of overlapping hard spheres. The investigations are performed for pores of different width, at different densities of the bulk fluid which is in an equilibrium with the confined fluid and for different degrees of bulk fluid association. The bulk fluid is described by using the Percus-Yevick approximation. A wide range of thermodynamic states and different bonding lengths between the reactants are investigated. It is shown that the effect of a chemical reaction in the bulk fluid produces qualitative changes in the behaviour of the den...

The direct correlation function of the complex discrete potential model fluids is obtained as a linear combination of the first-order mean spherical approximation (FMSA) solution for the simple square well model that has been reported recently [Hlushak et al., J. Chem. Phys. 130, 234511 (2009)]. The theory is employed to evaluate the structure and thermodynamics of complex fluids based on the square well-barrier and square well-barrier-well discrete potential models. Obtained results are compared with theoretical predictions of the hybrid mean spherical approximation, already reported in the literature [Guillen-Escamilla et al., J. Phys.: Condens. Matter 19, 086224 (2007)], and with computer simulation data of this study. The compressibility route to thermodynamics is then used to check whether the FMSA theory is able to predict multiple fluid–fluid transitions for the square barrier-well model fluids.

The mean spherical approximation integral equation is solved for a pair of large charged hard spheres in an ion-dipole mixture. In this work, the effect of the molecular nature of the solvent is taken into account approximately. Extra terms, not included in the DLVO theory, are found and are significant. The effect of dipole alignment near the macroions is repulsive at large separation but can be attractive at short separations.

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...