T. Staszewski

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.

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.

Phase behavior of a fluid confined in slitlike pores with walls modified by preadsorbed chain molecules

We have studied the microscopic structure, thermodynamics of adsorption, and phase behavior of Lennard-Jones fluid in slitlike pores with walls modified due to preadsorption of chain molecules. The chain species are grafted at the walls by terminating segments. Our theoretical considerations are based on a density functional approach in the semigrand canonical ensemble. The applied constraint refers to the constant number of grafted chain molecules in the pore without restriction of the number of chains at each of the walls. We have observed capillary condensation of Lennard-Jones fluid combined with the change of the distribution of chains from nonsymmetric to symmetric with respect to the pore walls. The phase diagrams of the model are analyzed in detail, dependent on the pore width, length of chains, and grafted density.

Phase behavior of decorated soft disks in two dimensions

Molecular dynamics simulations are used to investigate the phase behavior of disks decorated with small ligands in two-dimensional films. We consider disks with four ligands, which are fixed at vertices of a square or slide over the circle delimiting the core. For selected model systems, phase diagrams are evaluated and discussed. We show that ligand mobility can change the topology of phase diagrams. In particular, it can affect fluid-solid transitions, changing the solid phase symmetry. Moreover, the mobility of ligands can either hamper or facilitate crystallization.

Adsorption of short chains in slitlike pores: a quantitative comparison between density functional approach and Monte Carlo simulations

A density-functional and Monte Carlo simulation study of adsorption of short chains confined in slitlike pores is presented. The molecules are modelled as freely jointed tangent hard spheres. Each molecule consists of one surface-binding segment that interacts with the pore wall via Lennard-Jones (9,3) potential and a number of segments, which interact with the surface via hard-wall potentials. We have investigated the effects of a position of the surface-binding segment in the chain, the length of the chain, the width of the pore and the bulk phase density on properties of the fluid. We have found that a position of the adsorbing segment in the chain considerably affected a structure of the fluid. The theoretical results are compared with Monte Carlo simulations. The agreement between theoretical predictions and simulation data is excellent.

Monte Carlo simulations of a model two-dimensional, two-patch colloidal particles.

We carried out Monte Carlo simulations of the two-patch colloids in two-dimensions. Similar model investigated theoretically in three-dimensions exhibited a re-entrant phase transition. Our simulations indicate that no re-entrant transition exists and the phase diagram for the system is of a swan-neck type and corresponds solely to the fluid-solid transition.

Integral equations theory for two-dimensional systems involving nanoparticles*

ABSTRACT We employ integral equation approach to describe the angular-dependent correlation functions of two-dimensional systems of selected model of nanoparticles. The numerical calculations are performed without expanding correlation functions into series of orthogonal functions of angles. We also propose reference-averaged Mayer potential to calculate the angular-independent radial distribution functions between nanoparticles. The results of theoretical calculations are compared with molecular dynamics simulation data.

Adsorption on chemically bonded chain layers with embedded active groups

We use density functional theory to investigate adsorption on the solid surfaces modified with end-grafted chains with embedded attractive groups. The chains are modelled as freely joined spheres. They consist of segments A and a short block of segments B that mimics the functional group. The fluid molecules are spherical. All species interact via the Lennard-Jones (12-6) potential. The substrate is inert with respect to the chain segments and free molecules. We investigate the impact of the position of the B-block on adsorption of pure fluids, adsorption from binary solutions, the selectivity of the adsorption systems as well as on the structure of the bonded phase.