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S Sokołowski

Publications and source records attributed to S Sokołowski.

26 records · Page 2Linked to original sources
PubMed2004

Bulk and interfacial properties of binary polymer mixtures.

A microscopic density functional theory is used to investigate a binary mixture of polymers, built of freely jointed tangent hard spheres. The difference in the chain length and in the segment diameter of polymers gives rise to a demixing transition. We evaluate the bulk fluid phase equilibria (binodal) and the limit of stability of a mixed state (spinodal) for selected systems, and analyze the decay of the critical packing fraction, critical mole fraction, and critical pressure with an increase of the chain length. The bulk results are subsequently used in the calculations of the density profiles across the fluid-fluid interface. The obtained profiles are smooth and do not exhibit any oscillations on the length scale of the segment diameter. Upon approaching the critical point the interfacial tension vanishes as (Deltarho)3, where Deltarho is the difference between bulk densities of one component in bulk phases rich and poor in that species. This indicates that the microscopic density functional theory applied here is of a mean-field type.

Journal Article↗
PubMed2004

The structure of fluids confined in crystalline slitlike nanoscopic pores: bilayers.

Grand canonical and canonical ensemble Monte Carlo simulation methods are used to study the structure and phase behavior of Lennard-Jones fluids confined between the parallel (100) planes of the face centered cubic crystal. Ultra thin slit pores of the width allowing for the formation of only two adsorbate layers are considered. It is demonstrated that the structure of adsorbed phases is very sensitive to the wall-wall separation and to the strength of the fluid-wall potential. It is also shown that the structure of low temperature (solid) phases strongly depends on the fluid density. In particular, when the surface field is sufficiently strong, then the high density phases may exhibit a domain wall structure, quite the same as found in monolayer films adsorbed at a single substrate wall. On the other hand, the weakening of the surface potential leads to the regime in which only the hexagonally ordered bilayer structure is stable. The phase diagrams for a series of systems are estimated. It is shown that, depending on the pore width and the temperature, the condensation leads to the formation of the commensurate or incommensurate phases. The incommensurate phases may have the domain-wall or the hexagonal structure depending on the pore width and the strength of the fluid-wall potential.

Journal Article↗
PubMed2004

Lennard-Jones fluids confined in nanoscopic slits: evidence for reentrant filling transitions.

By using grand canonical and canonical ensemble Monte Carlo simulations, the structure and phase behavior of a Lennard-Jones (LJ) fluid confined between the parallel (100) planes of a face-centered cubic crystal are studied. Slit pores with a width which allows three adsorbate layers to form are used. It is shown that the filled pore consists of three commensurate layers over a wide range of the surface potential strength, while the pore-filling mechanism and the topology of the phase diagram change when the strength of this fluid-wall potential is varied. Condensation may occur in one step or via two layering-like transitions. The structure of monolayer films depends on the strength and corrugation of the surface potential, and the condensation of the middle layer may induce a reentrant first-order transition.

Journal Article↗
PubMed2003

Wetting behavior of associating binary mixtures at attractive walls: a lattice Monte Carlo study.

The lattice gas model is used to study the effects of molecular association on the wettability of surfaces with attractive walls by binary symmetric associating mixtures. The model assumes that the adsorbate particles occupy a regular cubic lattice of sites and that the interactions between adsorbate particles involve only the first nearest neighbors. The energies of interaction between the pairs of like particles are the same, while the only interaction between a pair of unlike particles is due to association. Only the formation of dimers is allowed and the energy of association is finite. The particles are subject to the surface, van der Waals-like potential, assumed to be the same for both components. The model is studied with the help of the Monte Carlo simulation method in the grand canonical ensemble. Only the ground state properties are treated analytically. It is demonstrated that, in general, molecular association hinders wetting. In particular, in the systems with nonzero wetting temperature, the increase of the association energy leads to the increase of the wetting temperature and for sufficiently high energy of association the mixture does not wet the surface at all. When the system is expected to exhibit complete wetting at the ground state, the film formed by strongly associating mixtures wets the surface only at sufficiently low temperatures, below the dewetting temperature. It is demonstrated that the dewetting temperature increases with the strength of the surface potential as well as with the increase of the association energy.

Journal Article↗
PubMed2003

Phase behavior of lattice associating binary mixtures: a Monte Carlo study.

The lattice gas model is used to study effects of molecular association on the phase behavior of binary symmetric mixtures, in which only dimers consisting of different particles can form. It is demonstrated that the increase of the association energy leads to qualitative changes of the phase diagrams. In particular, the demixing transition is observed only for sufficiently low association energy. That demixing transition can be either first order or continuous. For sufficiently high energy of association the condensed phase shows a very well ordered structure even at high temperatures.

Journal Article↗
PubMed2000

Density-functional theory for an electrolyte confined by thin charged walls.

Results are reported for the primitive model of an electrolyte and for the solvent primitive model of an electrolyte for the case where these fluids are confined by two charged walls. When the walls are thin, the confined electrolyte inside the walls is affected by the charge on both the inside and the outside of the walls. In the case of the primitive model (PM), this system has been studied previously using a singlet integral equation. Our density-functional (DF) study is more general because the fluids inside and outside the walls are constrained to have the same chemical potential and because solvent effects are considered, albeit at a crude level. The singlet integral equation does not consider the chemical potential constraint explicitly. We find that for the low density PM, the DF and integral equation approaches yield, except for a very narrow pore, very similar results. When solvent molecules are considered, the profiles become oscillatory. The co-ion density profiles are particularily interesting because the repulsive electrostatic potential and the effect of the increased pressure in "pushing" the co-ions against the wall compete.

Electrolytes↗