Biomedical subjects

Stefan Sokolowski

Publications and source records attributed to Stefan Sokolowski.

4 recordsLinked to original sources

PubMed2005

Capillary condensation of short-chain molecules.

A density-functional study of capillary condensation of fluids of short-chain molecules confined to slitlike pores is presented. The molecules are modeled as freely jointed tangent spherical segments with a hard core and with short-range attractive interaction between all the segments. We investigate how the critical parameters of capillary condensation of the fluid change when the pore width decreases and eventually becomes smaller than the nominal linear dimension of the single-chain molecule. We find that the dependence of critical parameters for a fluid of dimers and of tetramers on pore width is similar to that of the monomer fluid. On the other hand, for a fluid of chains consisting of a larger number of segments we observe an inversion effect. Namely, the critical temperature of capillary condensation decreases with increasing pore width for a certain interval of values of the pore width. This anomalous behavior is also influenced by the interaction between molecules and pore walls. We attribute this behavior to the effect of conformational changes of molecules upon confinement.

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PubMed2001

Capillary Condensation in Pores with Energetically Heterogeneous Walls: Density Functional versus Monte Carlo Calculations.

We investigate adsorption of a Lennard-Jones fluid in slit-like pores with energetically heterogeneous walls by using Grand Canonical Monte Carlo simulations and a density functional approach. The model of a fluid-wall potential is qualitatively similar to that invoked by Röcken et al. (J. Chem. Phys. 108, 8089, (1999); i.e., it consists of a homogeneous part that varies in the direction perpendicular to the wall and a periodic part, varying also in one direction parallel to the wall, but in contrast to the above mentioned work, both parts of the fluid-wall potential are modeled by Lennard-Jones (9, 3) type functions. The structure of the adsorbed film is characterized by local densities. We evaluate the phase diagrams for several systems characterized by different corrugation of the adsorbing potential and discuss the discrepancies between theoretical predictions and computer simulations. Copyright 2001 Academic Press.

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PubMed2001

Adsorption and Phase Transitions in Slit-like Pores with Differently Adsorbing Walls.

We study the adsorption of a lattice gas in a slit-like pore with different walls. The density profiles are evaluated in the framework of the mean-field approximation. We show that changes in the potential field exerted by one wall can lead to substantial modifications of the phase behavior of the fluids. Copyright 2001 Academic Press.

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PubMed2001

Density Functional Study of a Simple Membrane Using the Solvent Primitive Model.

The model membrane, whose surfaces are maintained at the differing surface potentials, V(1) and V(2), on its inner and outer surfaces, that has been studied previously is extended to include explicit solvent molecules. The solvent primitive model, where the solvent molecules are treated as hard spheres, is used. In this study, the electrolyte can interact with the membrane both electrostatically and by means of a short-range van der Waals-like potential that can be attractive or repulsive. The bulk fluid beyond the outer surface is a four-component electrolyte consisting of the hard sphere solvent, two species of cations, and one species of anions. The membrane is impermeable to one of the cation species so that the fluid in the membrane and beyond the inner surface is a three-component electrolyte. Previously, we studied this model membrane by computer simulation and density functional theory (DFT) and found this theory to be quite accurate. Here we report further results, obtained using DFT, from which results can be obtained much more easily than from simulations. The density profiles of the electrolyte near the membrane and the charge-potential relationship of the membrane surfaces under a wider variety of conditions than is possible by simulation are studied. The presence of the solvent molecules leads to a greater excluded volume. As a result, the density profiles are oscillatory, whereas they are monotonic when a molecular model for the solvent is not used. The potential versus charge relationship is strongly influenced by the solvent density. In addition to the electrostatic interactions, the effect of a van der Waals interaction on the solvent molecules is considered. Copyright 2001 Academic Press.

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