Stefan Sokołowski

Lennard-Jones mixtures in slit-like pores: a comparison of simulation and density-functional theory

The adsorption of binary Lennard-Jones mixtures in narrow slit-like pores is studied theoretically and by simulation. The model parameters are chosen to correspond to Ar-Kr mixtures in a carbon pore. The theoretical approach is based upon application of the Meister-Kroll-Groot version of density-functional theory, while simulation studies are carried out by using a constant-temperature molecular-dynamics method. In order to determine the state of the bulk fluid in equilibrium with the simulated system, chemical potentials of both components are determined during simulation runs using the particle-insertion method. The investigations are performed at three reduced temperatures T* = 2, 1·5 and 1·0, taking the argon-argon potential depth as reference. At the lowest temperature we concentrated on the gas-liquid transition in the pore. It is found that the theory considered provides a good description of the fluid structure inside the pore and that it also reproduces the phase behaviour of the system observed ...

Temperature dependence of the double layer capacitance for the restricted primitive model of an electrolyte solution from a density functional approach

We apply a different version of the density functional theory, given by Pizio, Patrykiejew, and Sokolowski [J. Chem. Phys. 121, 11957 (2004)], for a nonuniform restricted primitive model of an electrolyte solution to evaluate the temperature dependence of the capacitance of an electric double layer. We show that this theory is capable of reproducing the computer simulation data at a quantitative level. In particular, the reversal of the temperature dependence of the capacitance at low temperatures is predicted. This phenomenon has been difficult to predict from theory. Further, this theory also leads to an accurate description of the double layer structure.

Molecular dynamics simulation of size segregation in three dimensions

We report the first three-dimensional molecular dynamics simulation of particle segregation by shaking. Two different containers are considered: one cylindrical and another with periodic boundary conditions. The dependence of the time evolution of a test particle inside the material is studied as a function of the shaking frequency and amplitude, damping coefficients, and dispersivity.

GRAIN NON-SPHERICITY EFFECTS ON THE ANGLE OF REPOSE OF GRANULAR MATERIAL

We use a site-site model to describe non-sphericity of particles composing a granular media. Specific effects of grain non-sphericity 011 the angle of repose are investigated. We report evidence indicating the possible existence of a shape-roughness threshold for grains: below it angles of repose are essentially the same as those obtained for spherical grains; above it there are pronounced changes 011 the angle of repose and it is possible to find rather large piles of grains.

Evaluation of liquid–vapor density profiles for associating fluids in pores from density-functional theory

Using density-functional theory we calculate density profiles of an associating fluid in slit like pores as functions of two variables: The distance from the pore wall and the distance along the pore axis. Attention is focused on evaluation of the profiles characterizing the coexistence between two confined phases. We also calculate changes in the grand canonical potential connected with the formation of an interface between two coexisting confined phases. Specific calculations have been carried out for the associating, chain forming Lennard-Jones fluid adsorbed in a slitlike pore.

The role of attractive intermolecular forces in the density functional theory of inhomogeneous fluids

The density functional theory of Meister and Kroll for nonuniform simple fluids [Phys. Rev. A 31, 4055, (1985)] is modified in order to take into account pair correlations in the attractive energy term. The theory is applied for the calculation of density profiles of argon in the case of the free liquid surface and in the case of adsorption on ‘‘solid carbon dioxide.’’ For the gas–liquid interface the theory yields dew and bubble densities, which are in good agreement with computer simulations. For the adsorption of argon on solid CO2, the first‐order thin‐film to thick‐film transition is confirmed.

Simulation and density functional study of a simple membrane separating two restricted primitive model electrolytes

A simple membrane, supporting charge densities σ1 and σ2=−σ1 on its inner and outer surfaces, is considered. In addition to the electrostatic potential, the membrane interacts with the surrounding fluid by a short range van der Waals-like potential. The fluid beyond the outer surface is a three-component restricted primitive electrolyte consisting of two cations and one anion. The membrane is impermeable to one of the cations so that the fluid in the membrane and beyond the inner surface is a two-component restricted primitive electrolyte. We use Monte Carlo simulations and density functional theory to study the density profiles of the electrolyte and the charge-electrostatic potential relationship for the membrane surfaces. Even though σ2=−σ1, the potentials on the membrane surfaces are not equal and opposite. We also study a membrane consisting of a single charged plane. For both models, the density functional results are in good agreement with the simulations.

Molecular dynamics simulation of powder fluidization in two dimensions

Abstract We report model calculations of a fluidized state in two-dimensional packing of spherical beads subjected to vertical vibrations as recently experimentally studied by Clement and Rajchenbach. Using molecular dynamics we calculate the density field and the velocity distributions of the beads. We discuss the concept of fluidization and propose new ways to characterize it.

Classical multicomponent fluid structure near solid substrates: Born-Green-Yvon equation versus density-functional theory

We report a study of adsorption of binary mixtures of hard spheres of different sizes on a hard wall by using a version of density-functional theory, the Born-Green-Yvon (BGY) equation and Monte Carlo simulations. Following the BGY approach introduced by Fischer and Methfessel for single-component fluids, the proposed extension uses coarse-grained densities to approximate the contact values of pair distribution function of hard spheres. A procedure for evaluation of the coarse-grained densities, leading to an exact theory in one dimension, is proposed. The density-functional theory employed here, however, uses the Meister-Kroll and Groot approach. Comparisons of theoretical calculations with Monte Carlo simulations, as well as with previous theoretical predictions, have shown that density-functional theory reproduces the pseudo-experimental data accurately, even for extremely large size ratios of molecules of both species. The accuracy of the predictions of the BGY approach is less satisfactory, and for h...

Influence of humic acid on surface fractal dimension of kaolin: analysis of mercury porosimetry and water vapour adsorption data

Abstract Samples of kaolin amended with different amounts of humic acid extracted from a Cambic Areosol under forest are investigated. We measure water vapour adsorption isotherms and mercury intrusion pore size distributions. Experimental adsorption isotherms are analyzed by means of Frenkel–Hill–Halsey (FHH) type equation. This analysis leads to the determination of the surface fractal dimension. The fractal dimensions obtained from adsorption isotherms are next compared with those resulting from the analysis of mercury intrusion data. The calculations performed indicate consistently fractally rough surface structure for all the samples. However, the changes of the surface properties of the samples are not proportional to the amount of humic acid added. The fractal dimension is the highest for untreated kaolin, attains a minimum for samples with a small amount of humic acid added and smoothly increases to a constant value, which is significantly lower than that characteristic for pure humic acid.