Joanna Reszko-Zygmunt

Adsorption of nitrogen and water vapor by alluvial soils

Abstract We report on the results of investigations on the adsorption of nitrogen at 79 K and water vapor at 293 K on several Polish alluvial soils. The experimental adsorption data have been used to evaluate the surface fractal dimension from Frenkel–Halsey–Hill (FHH) equation and to evaluate the adsorption energy distribution function by using a modified numerical method that has been developed by Stanley and Guiochon [J. Phys. Chem. 97 (1993) 8098–8102] for non-fractal adsorbents. We have investigated the correlations between the surface fractal dimensions and the average values of the adsorption energy with several physico-chemical properties of soils. We have found that these quantities correlate with the content of the clay fraction and with the cation exchange capacity. We did not find any correlation between the geometric or energetic heterogeneity parameters and the content of the organic matter.

Phase behaviour of a Lennard-Jones fluid in a pore with permeable walls of a finite thickness: a density functional approach

A confinement of a Lennard-Jones fluid in a system of slitlike pores separated by semipermeable walls of a finite width is studied. The walls are modelled by square-well repulsive potential wells. The structure of the confined fluid is investigated by means of a density functional method. For high potential barriers separating the pores, the phase behaviour of the system is similar to that for a single slitlike pore with impenetrable walls. For intermediate and low potential barriers the system shows different phase behaviour. Within some temperature range the isotherms exhibit two hysteresis loops, which characterize the condensation of the fluid in different parts of the system, namely in the pore and inside the semipermeable walls. The systems characterized by low and intermediate potential barriers exhibit the triple point, such that at temperatures below that triple point the condensation instantaneously takes place in both the pore and inside the permeable wall.

Microscopic structure and properties of an interface between coexisting phases of an associating fluid adsorbed in slitlike pores.

Using density functional theory, we calculate density profiles of an associating fluid in slitlike pores. These profiles characterize an interface between two coexisting, adsorbed phases, e.g., between gaseous and liquid phases formed during capillary condensation. Our study has been carried out for weakly, as well as for strongly, associated fluids confined in pores of different widths. We also investigate the role of the fluid-wall interaction.

Phase coexistence and interface structure of a two-component Lennard-Jones fluid in porous media: application of Born—Green—Yvon equation

The Born-Green-Yvon equation with smoothed density approximation is used to calculate the liquid-liquid density profiles of a symmetric Lennard-Jones fluid in a hard sphere disordered matrix. The phase diagrams are evaluated for model systems characterized by different matrix densities and compared with the results of theoretical predictions and the Monte Carlo simulations of Gordon, P. A., and Glandt, E. D., 1996, J. chem. Phys., 105, 4257. It was found that increasing the matrix packing fraction reduces the magnitude of the miscibility gap and smooths the density profiles between two coexisting phases.

The influence of random changes in the adsorbing potential on phase transitions in a Lennard-Jones fluid confined to energetically heterogeneous slit-like pores

A density functional approach is used to study the adsorption and phase behaviour of a Lennard-Jones (LJ) fluid in slit-like pores with energetically heterogeneous walls, investigating how the randomly varying part of the fluid-solid potential imposed on a periodic ‘back-ground’ potential modifies the phase behaviour of the confined fluid. Non-local density functional theory is employed to describe the system. To study the system with a random external field, the method used is based on investigations of several replicas of the system and on averaging the final thermodynamic results over the replicas.

The phase behaviour of a fluid in a slitlike pore with permeable walls

The confinement of a lattice fluid in a set of slitlike pores separated by semipermeable walls with a finite width has been studied. The walls are modelled by a square-well repulsive potential with a finite height. The thermodynamic properties and the phase behaviour of the system are evaluated by means of Monte Carlo simulations. For some states theoretical calculations have been made using a mean-field-type theory. These investigations confirm previous findings for confined Lennard-Jones fluids, obtained from a density functional approach. For intermediate and low potential barriers that separate the pores, the isotherms exhibit two hysteresis loops and the liquid-vapour coexistence curve divides into two branches describing condensation inside the pore and inside the permeable wall. These two branches are separated by a triple point. At temperatures lower than the triple point temperature, the condensation takes place instantaneously in both the pore and inside the permeable wall. It was found that when the temperature is scaled by the bulk critical temperature, the phase diagram emerging from this simple mean-field treatment is close to the phase diagram obtained from simulation.