S Sokołowski

Maria Curie-Sklodowska University in Lublin, Lyublin, Lublin Voivodeship, Poland

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Publications (189)387.74 Total impact

  • O. Pizio, S. Sokołowski
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    ABSTRACT: We investigate the electric double layer formed between charged walls of a slit-like pore and a solvent primitive model (SPM) for electrolyte solution. The recently developed version of the weighted density functional approach for electrostatic interparticle interaction is applied to the study of the density profiles, adsorption and selectivity of adsorption of ions and solvent species. Our principal focus, however, is in the dependence of differential capacitance on the applied voltage, on the electrode and on the pore width. We discuss the properties of the model with respect to the behavior of a primitive model, i.e., in the absence of a hard-sphere solvent. We observed that the differential capacitance of the SPM on the applied electrostatic potential has the camel-like shape unless the ion fraction is high. Moreover, it is documented that the dependence of differential capacitance of the SPM on the pore width is oscillatory, which is in close similarity to the primitive model.
    07/2014;
  • A. Patrykiejew, S. Sokołowski
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    ABSTRACT: Using a simple one-dimensional Frenkel-Kontorowa type model, we have demonstrated that finite commensurate chains may undergo the commensurate-incommensurate (C-IC) transition when the chain is contaminated by isolated impurities attached to the chain ends. Monte Carlo (MC) simulation has shown that the same phenomenon appears in two-dimensional systems with impurities located at the peripheries of finite commensurate clusters.
    07/2014;
  • M Borówko, S Sokołowski, T Staszewski
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    ABSTRACT: We use density functional theory to study the influence of fluid adsorption on the structure of grafted chain layer. The chains are modeled as freely jointed spheres. The chain segments and spherical molecules of the fluid interact via the Lennard-Jones potential. The fluid molecules are attracted by the substrate. We calculate the excess adsorption isotherms, the average height of tethered chains, and the force acting on selected segments of the chains. The parameters that were varied include the length of grafted chains, the grafting density, the parameters characterizing fluid-chain and fluid-surface interactions, the bulk fluid density, and temperature. We show that depending on the density of the bulk fluid the height of the bonded layer increases, remains constant, or decreases with increasing temperature.
    The Journal of chemical physics. 06/2014; 140(23):234904.
  • O Pizio, S Sokołowski, Z Sokołowska
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    ABSTRACT: We investigate microscopic structure, adsorption, and electric properties of a mixture that consists of amphiphilic molecules and charged hard spheres in contact with uncharged or charged solid surfaces. The amphiphilic molecules are modeled as spheres composed of attractive and repulsive parts. The electrolyte component of the mixture is considered in the framework of the restricted primitive model (RPM). The system is studied using a density functional theory that combines fundamental measure theory for hard sphere mixtures, weighted density approach for inhomogeneous charged hard spheres, and a mean-field approximation to describe anisotropic interactions. Our principal focus is in exploring the effects brought by the presence of ions on the distribution of amphiphilic particles at the wall, as well as the effects of amphiphilic molecules on the electric double layer formed at solid surface. In particular, we have found that under certain thermodynamic conditions a long-range translational and orientational order can develop. The presence of amphiphiles produces changes of the shape of the differential capacitance from symmetric or non-symmetric bell-like to camel-like. Moreover, for some systems the value of the potential of the zero charge is non-zero, in contrast to the RPM at a charged surface.
    The Journal of Chemical Physics 05/2014; 140(17):174706. · 3.12 Impact Factor
  • Source
    S. Sokołowski, J. Ilnytskyi, O. Pizio
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    ABSTRACT: Many objects of nanoscopic dimensions involve fluid-tethered chain interfaces. These systems are of interest for basic science and for several applications, in particular for design of nanodevices for specific purposes. We review recent developments of theoretical methods in this area of research and in particular of density functional (DF) approaches, which provide important insights into microscopic properties of such interfaces. The theories permit to describe the dependence of adsorption, wettability, solvation forces and electric interfacial phenomena on thermodynamic states and on characteristics of tethered chains. Computer simulations for the problems in question are overviewed as well. Theoretical results are discussed in relation to simulation results and to some experimental observations.
    03/2014;
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    ABSTRACT: We apply a density functional theory to calculate the solvation force in the system involving Janus particles confined between two planar walls. Janus particles are modeled as spheres composed of attractive and repulsive parts and their orientation is described by the vectors representing internal degrees of freedom. We consider the cases of pores with identical walls, as well as the pores with competing walls (the so-called Janus-like pores). The density functional approach we employ combines fundamental measure theory with a mean-field approximation for the anisotropic interparticle interaction. We study how the solvation force and the orientational structure of confined particles depend on the competition between the surface field and the interactions between confined molecules and on the parameters of the model such as temperature and density. It is shown that the anisotropic interaction between the confined molecules and the character of the walls significantly influence the solvation force.
    The Journal of Chemical Physics 12/2013; 139(22):224711. · 3.12 Impact Factor
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    ABSTRACT: The structure of grafted chain layers immersed in an explicit solvent consisting of chain molecules is studied using density functional theory. We consider bonded layers built of short grafted chains at a moderate grafting density. We investigate the grafted layers in contact with oligomeric solvents and oligomer-monomer solutions. The chain molecules are freely jointed spherical segments. The substrate is assumed to be inert with respect to the grafted chains. The mobile molecules interact with the surface via Lennard-Jones (9-3) potential. The interactions between mobile chains, monomers, as well as segments of the tethered chains, are described by Lennard-Jones (12-6) potential. We discuss how the structure of the grafted chain layer depends on the length of mobile chains and strengths of grafted chain-oligomer, oligomer-substrate, oligomer-oligomer and oligomer-monomer interactions. We study the impact of mixture composition on the height of the bonded layer for selected model systems. The results are consistent with previous experimental and simulation data.
    The Journal of Physical Chemistry B 08/2013; · 3.61 Impact Factor
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    ABSTRACT: We propose application of density functional theory to calculate the force acting on a selected segment of a tethered polymer chain that leads to stretching the chain. The density functional allows one to determine the effects due to the presence of other chains and solvent molecules. For high and moderate solvent densities the plot of the force versus the distance of the segment from the surface exhibits oscillatory behavior that has not been predicted by other approaches.
    The Journal of Chemical Physics 05/2013; 138(20):204707. · 3.12 Impact Factor
  • Source
    Orest Pizio, Stefan Sokołowski
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    ABSTRACT: We apply a density functional theory to describe properties of a restricted primitive model of an ionic fluid in slit-like pores. The pore walls are modified by grafted chains. The chains are built of uncharged or charged segments. We study the influence of modification of the pore walls on the structure, adsorption, ion selectivity, and the electric double layer capacitance of ionic fluid under confinement. The brush built of uncharged segments acts as a collection of obstacles in the walls vicinity. Consequently, separation of charges requires higher voltages, in comparison to the models without brushes. At high grafting densities the formation of crowding-type structure is inhibited. The double layer structure becomes more complex in various aspects, if the brushes are built of charged segments. In particular, the evolution of the brush height with the bulk fluid density and with the charge on the walls depends on the length of the blocks of charged spheres as well as on the distribution of charged species along chains. We also investigated how the dependence of the double layer capacitance on the electrostatic potential (or on the charge on the walls) changes with grafting density, the chain length, distribution of charges along the chain, the bulk fluid density, and, finally, with the pore width. The shape of the electric double layer capacitance vs. voltage changes from a camel-like to bell-like shape, if the bulk fluid density changes from low to moderate and high. If the bulk density is appropriately chosen, it is possible to alter the shape of this curve from the double hump to single hump by changing the grafting density. Moreover, in narrow pores one can observe the capacitance curve with even three humps for a certain set of parameters describing brush. This behavior illustrates how strong the influence of brushes on the electric double layer properties can be, particularly for ionic fluids in narrow pores.
    The Journal of Chemical Physics 05/2013; 138(20):204715. · 3.12 Impact Factor
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    ABSTRACT: We investigate the structure and adsorption of amphiphilic molecules at planar walls modified by tethered chain molecules using density functional theory. The molecules are modeled as spheres composed of a hydrophilic and hydrophobic part. The pinned chains are treated as tangentially jointed spheres that can interact with fluid molecules via orientation-dependent forces. Our density functional approach involves fundamental measure theory, thermodynamic perturbation theory for chains and a mean-field approximation for describing the anisotropic interactions. We study the adsorption of the particles, focusing on the competition between the external field (due to the surface and due to attached chain molecules) and the interaction-induced ordering phenomena.
    The Journal of Physical Chemistry B 01/2013; · 3.61 Impact Factor
  • O Pizio, S Sokołowski, Z Sokołowska
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    ABSTRACT: We apply recently developed version of a density functional theory [Z. Wang, L. Liu, and I. Neretnieks, J. Phys.: Condens. Matter 23, 175002 (2011)] to study adsorption of a restricted primitive model for an ionic fluid in slit-like pores in the absence of interactions induced by electrostatic images. At present this approach is one of the most accurate theories for such model electric double layers. The dependencies of the differential double layer capacitance on the pore width, on the electrostatic potential at the wall, bulk fluid density, and temperature are obtained. We show that the differential capacitance can oscillate as a function of the pore width dependent on the values of the above parameters. The number of oscillations and their magnitude decrease for high values of the electrostatic potential. For very narrow pores, close to the ion diameter, the differential capacitance tends to a minimum. The dependence of differential capacitance on temperature exhibits maximum at different values of bulk fluid density and applied electrostatic potential.
    The Journal of Chemical Physics 12/2012; 137(23):234705. · 3.12 Impact Factor
  • Source
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    ABSTRACT: We use a version of the density functional theory to study the solvation force between two plates modified with a tethered layer of chains. The chains are built of tangentially jointed charged spherical segments. The plates are immersed in an electrolyte solution that involves cations, anions and solvent molecules. The latter molecules are modelled as hard spheres. We study the dependence of the solvation force and the structure of chains and of solute molecules on the grafting density, length of chains, architecture of the chains and on concentration of the solute.
    Condensed Matter Physics 10/2012; 15(3):33801:1-14. · 0.76 Impact Factor
  • M Borówko, S Sokołowski, T Staszewski
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    ABSTRACT: A density functional theory has been applied to study adsorption from oligomer-monomer solutions on solid surfaces modified with end-grafted polymers. Chains are modeled as freely jointed tangent spheres. All spherical species interact via Lennard-Jones (12-6) potential. The grafted chains are not attracted by the surface. Fluid molecules interact with the substrate via Lennard-Jones (9-3) potential. It is shown how a shape of the relative excess adsorption isotherms depends on such parameters as the oligomer length, the grafting density, oligomer-substrate interactions, oligomer-grafted chains interactions, and oligomer-monomer interactions in the bulk solution. As attractive interactions between free and grafted chains strengthen, the relative excess adsorption isotherm can change from negative, through S-shaped with an adsorption azeotropic point, to positive in the whole concentration region. A change of oligomer-monomer interactions causes the opposite effects. For low grafting densities of attractive bonds, the relative excess of oligomers increases, reaches a maximum, and decreases. The structure of surface layers is also analyzed.
    The Journal of Physical Chemistry B 10/2012; 116(42):12842-9. · 3.61 Impact Factor
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    ABSTRACT: 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.
    The Journal of Chemical Physics 08/2012; 137(7):074707. · 3.12 Impact Factor
  • Source
    L. B. Bhuiyan, D. Henderson, S. Sokołowski
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    ABSTRACT: A recently proposed local second contact value theorem [Henderson D., Boda D., J. Electroanal. Chem., 2005, 582, 16] for the charge profile of an electric double layer is used in conjunction with the existing Monte Carlo data from the literature to assess the contact behavior of the electrode-ion distributions predicted by the density functional theory. The results for the contact values of the co- and counterion distributions and their product are obtained for the symmetric valency, restricted primitive model planar double layer for a range of electrolyte concentrations and temperatures. Overall, the theoretical results satisfy the second contact value theorem reasonably well, the agreement with the simulations being semi-quantitative or better. The product of the co- and counterion contact values as a function of the electrode surface charge density is qualitative with the simulations with increasing deviations at higher concentrations.
    07/2012;
  • W.rŻysko, O.pizio, S.sokoŁowski
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    ABSTRACT: We study the capillary condensation of a lattice gas with nearest neighbor attraction confined to a slit-like pore filled with frozen obstacles (matrix). First, the lattice Monte Carlo simulations were performed for a slit-like pore without obstacles. Next, the pore filled with obstacles, i.e., confined microporous medium, is prepared by adsorbing and then by quenching a hard sphere fluid in the pore of the width H. The model includes fluid-wall attraction; however, the fluid-matrix interaction is entirely repulsive. We have investigated how concentration of obstacles and the pore width H influence the capillary phase diagrams. Our numerical experiments reveal essential changes in the critical temperature and in the shape of the coexistence line with the amount of quenched obstacles.
    International Journal of Modern Physics C 04/2012; 10(05). · 0.62 Impact Factor
  • A Patrykiejew, S Sokołowski
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    ABSTRACT: Using the results of extensive Monte Carlo simulations in the canonical and grand canonical ensembles, we discuss the phase behavior of mixed submonolayer films of krypton and xenon adsorbed on the graphite basal plane. The calculations have been performed using two- and three-dimensional models of the systems studied. It has been demonstrated that out-of-plane motion does not affect the properties of the films as long as the total density is well below the monolayer completion and at moderate temperatures. For the total densities close to the monolayer completion, the promotion of particles to the second layer considerably affects the film properties. Our results are in a reasonable agreement with the available experimental data. The melting point of submonolayer films has been shown to exhibit non-monotonous changes with the film composition, and reaches minimum for the xenon concentration of about 50%. At the temperatures below the melting point, the structure of solid phases depends upon the film composition and the temperature; one can also distinguish commensurate and incommensurate phases. Two-dimensional calculations have demonstrated that for the xenon concentration between about 15% and 65% the adsorbed film exhibits the formation of a superstructure, in which each Xe atom is surrounded by six Kr atoms. This superstructure is stable only at very low temperatures and transforms into the mixed commensurate (√3×√3)R30° phase upon the increase of temperature. Such a superstructure does not appear when a three-dimensional model is used. Grand canonical ensemble calculations allowed us to show that for the xenon concentration of about 3% the phase diagram topology of monolayer films changes from the krypton-like (with incipient triple point) to the xenon-like (with ordinary triple point).
    The Journal of Chemical Physics 04/2012; 136(14):144702. · 3.12 Impact Factor
  • M Borówko, S Sokołowski, T Staszewski
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    ABSTRACT: A density functional study of adsorption from binary solutions on surfaces modified with tethered chains is presented. The tethered chains are modeled as freely jointed tangent spheres. The fluid molecules are spherical. All species interact via the Lennard-Jones (12-6) potential. The substrate is neutral with respect to all chain segments but the surface-binding segment, and it interacts with the fluid molecules via a Lennard-Jones (9-3) potential. Depending on the parameters of the model, different shapes of the relative excess adsorption isotherms are found. The density profiles of all components are analyzed. It is shown that the surface region is highly inhomogeneous. An influence of the grafting density, the length of grafted chains, the nature of the solution, and its composition on the adsorption mechanism and the structure of the bonded-phase is investigated. The theoretical predictions are consistent with the results of computer simulations and experimental data.
    The Journal of Physical Chemistry B 03/2012; 116(10):3115-24. · 3.61 Impact Factor
  • Source
    M. Borówko, A. Patrykiejew, O. Pizio, S. Sokołowski
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    ABSTRACT: We use a version of the density functional theory to study the changes in the height of the tethered layer of chains built of jointed spherical segments with the change of the length and surface density of chains. For the model in which the interactions between segments and solvent molecules are the same as between solvent molecules we have discovered two effects that have not been observed in previous studies. Under certain conditions and for low surface concentrations of the chains, the height of the pinned layer may attain a minimum. Moreover, for some systems we observe that when the temperature increases, the height of the layer of chains may decrease.
    02/2012;
  • A. Patrykiejew, W. Rżysko, S. Sokołowski
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    ABSTRACT: Using Monte Carlo simulation methods in the canonical and grand canonical ensembles, we study the melting and the structure of low-temperature phases of mixed Ar–Kr submonolayer films on graphite. It is shown that such films exhibit a complete mixing in the liquid phase and freeze into a mixed solid phase, independently of the composition. The structure of the solid phase, however, depends upon the film composition, its total density, and the temperature. For submonolayer coverages, when the mole fraction of Kr is lower than about 0.1, the mixture freezes into the incommensurate, argon-like phase. For the higher mole fractions of Kr, the freezing leads to the formation of a mixed commensurate (√3 × √3)R30° phase. The lowering of temperature leads to structural phase transitions in the solid. When the krypton mole fraction is lower than about 0.88, the transition leads to the formation of domain-wall structures, in which the commensurate domains are made of krypton atoms, while the composition of walls depends upon the Kr mole fraction. It is shown that even rather small concentrations of argon atoms can trigger the commensurate–incommensurate transition. For still higher Kr mole fractions, exceeding about 0.88, the commensurate, krypton-like, solid phase is stable at any temperatures below the melting point. At sufficiently low temperatures, the phase separation takes place and argon atoms are removed from the film interior to the peripheries of submonolayer. In the case of films with the total density close to the monolayer completion, the commensurate structure shows much higher stability. It is demonstrated, however, that it is an artifact of the simulation methods used and, in particular, of the periodic boundary conditions applied, rather than a real phenomenon. It is also demonstrated that the phase diagram topology of monolayer films changes with the film composition. In particular, the vapor–liquid critical point appears only when krypton concentration is lower than about 0.45.
    The Journal of Physical Chemistry C. 12/2011; 116(1):753–763.

Publication Stats

767 Citations
387.74 Total Impact Points

Institutions

  • 1978–2014
    • Maria Curie-Sklodowska University in Lublin
      • • Department for The Modelling of Physicochemical Processes
      • • Faculty of Chemistry
      • • Institute of Biology and Biochemistry
      • • Department of Theoretical Chemistry
      Lyublin, Lublin Voivodeship, Poland
  • 2005–2013
    • Universidad Nacional Autónoma de México
      • Institute of Chemistry
      Mexico City, The Federal District, Mexico
    • Charles University in Prague
      • Ústav teoretické fyziky
      Praha, Hlavni mesto Praha, Czech Republic
  • 2012
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      Erlangen, Bavaria, Germany
  • 2011
    • National Academy of Sciences of Ukraine
      • Institute for Condensed Matter Physics
      Kharkiv, Kharkivs'ka Oblast', Ukraine
  • 1994–2011
    • Medical University of Lublin
      • Department of Physical Chemistry
      Lublin, Lublin Voivodeship, Poland
  • 1999–2009
    • Polish Academy of Sciences
      • Instytut Fizyki
      Warsaw, Masovian Voivodeship, Poland
    • Institute of Physics of the National Academy of Science of Ukraine
      Kievo, Kyiv City, Ukraine
  • 1995–2009
    • Metropolitan Autonomous University
      • Departamento de Física
      Ciudad de México, The Federal District, Mexico
  • 2006
    • University of Natural Resources and Life Science Vienna
      • Institut für Verfahrens- und Energietechnik (IVET)
      Vienna, Vienna, Austria
    • Centrum Onkologii-Instytut im. Marii Skłodowskiej-Curie
      Warszawa, Masovian Voivodeship, Poland
  • 1981–2004
    • Maria Skłodowska-Curie Institute of Oncology
      Cracovia, Lesser Poland Voivodeship, Poland
  • 1996–1999
    • Brigham Young University - Idaho
      • Department of Chemistry
      Mesa, Arizona, United States
  • 1998
    • Brigham Young University - Provo Main Campus
      • Department of Chemistry and Biochemistry
      Provo, UT, United States
  • 1992
    • Ruhr-Universität Bochum
      • Institut Thermo- und Fluiddynamik
      Bochum, North Rhine-Westphalia, Germany