M. Borówko

Density functional approach to the adsorption of spherical molecules on a surface modified with attached short chains

A density functional and Monte Carlo simulation study of end-grafted polymers immersed by simple fluids is presented. The polymer molecules are modeled as freely jointed tangent hard spheres with the end segments linked to the surface. The authors analyze an influence of the chain length, the grafting density, and a nature of solvent on the brush structure. Adsorption of hard-sphere mixtures on the modified surface is also discussed. The theory precisely approximates simulation data.

Gradient optimization in elution liquid chromatography : I. Theoretical considerations connected with evaluation of the concentration-time function for stepwise elution

Abstract Using the theoretical treatment of Jandera and Churacek, problems connected with evaluation of the concentration-time function are discussed. It is shown that the linear relationships of the type capacity factor versus concentration of the more efficient eluting component in the binary-solvent mobile phase, measured for different chromatographed compounds, can be used to predict the concentration-time function for stepwise elution with a mobile phase of constant composition in each step.

Gradient optimization in elution liquid chromatography : II. Theory of multi-step elution with a mobile phase of constant composition in each step

Abstract Equations describing multi-step elution with a mobile phase of constant composition in each step have been derived. These equations are very useful for calculating the concentration-time function if the experimental relationships between the capacity factors and the concentration of the more efficient eluting component in the binary-solvent mobile phase are known for different sample compounds.

Dependence of the capacity ratio on the composition of the binary mobile phase in liquid—solid adsorption chromatography

Abstract The dependence of the capacity ratio on the composition of the binary mobile phase is discussed in terms of Snyders treatment. The relationships obtained for the capacity ratio have been tested on experimental data. The derivation of the relationship for the capacity ratio discussed by Jandera and Churacek has been examined.

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.

Fractal dimension of peat soils from adsorption and from water retention experiments

Samples of peat soils characterized by different degree of the secondary transformation are studied by means of nitrogen and water vapor sorption. Moreover, we have also determined the water retention curves and the dependence of the hydraulic conductivity on water potential. The experimental data are interpreted in terms of fractal theories of adsorption and retention, yielding the values of the corresponding fractal dimensions. We discuss the relation between surface fractal dimensions obtained from nitrogen and water sorption data, as well as between the mass fractal dimension resulting from retention data. We have also tried to correlate the fractal dimensions to other physico-chemical properties of investigated soils.

Adsorption of ions on surfaces modified with brushes of polyampholytes

We apply density functional theory to study adsorption of ions, treated in the framework of the restricted primitive model (RPM), on surfaces modified by tethered polyampholytes. The residual electrostatic contribution to the free energy functional is approximated by using the approach proposed by Wang et al. [J. Phys.: Condens. Matter 23, 175002 (2011)] for simple nonuniform RPMs systems. Our research concentrates on the problems how the distribution of the charges within chains of polyampholytes changes the selectivity of adsorption of ions species, the structure of the surface layer, and its electric properties.

Adsorption of oligomers on the polymer-tethered surfaces

A density functional study of adsorption of oligomers on weakly attractive surfaces modified with grafted chains is presented. The chain molecules are modeled as freely jointed tangent spheres. The segments interact via Lennard-Jones (12-6) potentials. Two types of substrates are considered - a neutral surface and the Lennard-Jones (9,3) surface. The mechanism of adsorption is discussed. Depending on the system characteristics, the primary, secondary and ternary adsorption is found. The effects of selected factors on adsorption and separation of mixtures are analyzed.

A density functional approach to retention in chromatography with chemically bonded phases

A density functional approach to the retention in a chromatography with chemically bonded phases is developed. The bonded phase is treated as brush built of grafted polymers. The chain molecules are modelled as freely jointed spheres. Segments of all components interact with the surface via the hard wall potential whereas interactions between the segments are described by Lennard-Jones (12-6) potential. The structure of the bonded phase is investigated. The distribution of different solutes in the stationary phases is determined. An influence of the following parameters on the retention is analyzed: the grafting density, the grafted chains length, the strength of molecular interactions, the solute sizes, temperature. The theoretical predictions are consisted with numerous experimental results.

CHEMICAL REACTIONS AT SURFACES: APPLICATION OF THE REACTION ENSAMBLE MONTE CARLO METHOD

The Monte Carlo simulation method introduced by Smith and Triska [J. Chem. Phys.100 (1994) 3019] is extended to the case of a reacting fluid in contact with a hard wall. The fluid structure for both spherical and nonspherical reaction products is discussed for simple models of reacting hard spheres near a hard wall and near a wall interacting via Lennard-Jones (9,3) potential. In the latter case the investigated model assumes that the probability of a chemical reaction changes with a distance from the surface. It is shown that the applied technique is suitable for the study of reacting nonuniform fluids.