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S. Lamperski - One of the best experts on this subject based on the ideXlab platform.
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The planar electric double layer capacitance for the solvent Primitive Model electrolyte
Physical Chemistry Chemical Physics, 2015Co-Authors: S. Lamperski, Monika Pluciennik, Christopher W. OuthwaiteAbstract:The planar electric double layer capacitance of the solvent Primitive Model electrolyte is studied using simulation and two versions of the modified Poisson–Boltzmann theory. At small values of the surface charge and varying electrolyte concentration, the capacitance has a behaviour analogous to that of the restricted Primitive Model electrolyte. As the electrolyte concentration is increased at a fixed total packing fraction, the minimum at zero surface charge changes to a maximum. This qualitative change is predicted by both simulation and the modified Poisson–Boltzmann theories. The transition envelope, separating the change in the capacitance from a minimum to a maximum at zero surface charge, is shifted from the restricted Primitive Model value to higher ion densities at fixed total packing fractions.
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The electric double-layer differential capacitance at and near zero surface charge for a restricted Primitive Model electrolyte.
The journal of physical chemistry. B, 2009Co-Authors: S. Lamperski, Christopher W. Outhwaite, Lutful Bari BhuiyanAbstract:The behavior of the differential capacitance of a planar electric double layer containing a restricted Primitive Model electrolyte in the neighborhood of zero surface charge is investigated by theo...
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the electric double layer differential capacitance at and near zero surface charge for a restricted Primitive Model electrolyte
Journal of Physical Chemistry B, 2009Co-Authors: S. Lamperski, Christopher W. Outhwaite, L B BhuiyanAbstract:The behavior of the differential capacitance of a planar electric double layer containing a restricted Primitive Model electrolyte in the neighborhood of zero surface charge is investigated by theory and simulation. Previous work has demonstrated that at zero surface charge the differential capacitance has a minimum for aqueous electrolytes at room temperature but can have a maximum for molten salts and ionic liquids. The transition envelope separating the two situations is found for a modified Poisson-Boltzmann theory and a Poisson-Boltzmann equation corrected for the exclusion volume term. Good agreement is found between simulation and the modified Poisson-Boltzmann theory in the neighborhood of the envelope at the reduced temperature of 0.8, while the exclusion volume corrected Poisson-Boltzmann theory shows correct qualitative trends.
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differential capacitance of the solvent Primitive Model diffuse layer using the inhomogeneous poisson boltzmann theory with an exclusion volume term
Journal of Electroanalytical Chemistry, 2004Co-Authors: S. Lamperski, Christopher W. OuthwaiteAbstract:Abstract The solvent Primitive Model diffuse double layer capacitance is analysed using a Poisson–Boltzmann theory which incorporates the exclusion volume term in the Boltzmann distribution. Unequal ion and solvent sizes are considered and the differential capacitance calculated for 1:1 electrolytes at different electrolyte and solvent concentrations. The unequal ion sizes cause an asymmetry in the capacity curves while the solvent can radically influence its overall shape. At low electrolyte concentrations and small surface charge, the capacitance has a minimum which changes to a maximum as the electrolyte concentration increases. At the higher surface charge densities the capacity curve approaches limiting values, these values depending on the relative counterion size.
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exclusion volume term in the inhomogeneous poisson boltzmann theory for high surface charge
Langmuir, 2002Co-Authors: S. Lamperski, C. W. OuthwaiteAbstract:A restricted Primitive Model electrolyte in the neighborhood of a uniformly charged plane electrode is investigated at high surface charge using an improved Poisson−Boltzmann theory. A layering of counterions is found in agreement with Monte Carlo simulations.
Christopher W. Outhwaite - One of the best experts on this subject based on the ideXlab platform.
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The planar electric double layer capacitance for the solvent Primitive Model electrolyte
Physical Chemistry Chemical Physics, 2015Co-Authors: S. Lamperski, Monika Pluciennik, Christopher W. OuthwaiteAbstract:The planar electric double layer capacitance of the solvent Primitive Model electrolyte is studied using simulation and two versions of the modified Poisson–Boltzmann theory. At small values of the surface charge and varying electrolyte concentration, the capacitance has a behaviour analogous to that of the restricted Primitive Model electrolyte. As the electrolyte concentration is increased at a fixed total packing fraction, the minimum at zero surface charge changes to a maximum. This qualitative change is predicted by both simulation and the modified Poisson–Boltzmann theories. The transition envelope, separating the change in the capacitance from a minimum to a maximum at zero surface charge, is shifted from the restricted Primitive Model value to higher ion densities at fixed total packing fractions.
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The electric double-layer differential capacitance at and near zero surface charge for a restricted Primitive Model electrolyte.
The journal of physical chemistry. B, 2009Co-Authors: S. Lamperski, Christopher W. Outhwaite, Lutful Bari BhuiyanAbstract:The behavior of the differential capacitance of a planar electric double layer containing a restricted Primitive Model electrolyte in the neighborhood of zero surface charge is investigated by theo...
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the electric double layer differential capacitance at and near zero surface charge for a restricted Primitive Model electrolyte
Journal of Physical Chemistry B, 2009Co-Authors: S. Lamperski, Christopher W. Outhwaite, L B BhuiyanAbstract:The behavior of the differential capacitance of a planar electric double layer containing a restricted Primitive Model electrolyte in the neighborhood of zero surface charge is investigated by theory and simulation. Previous work has demonstrated that at zero surface charge the differential capacitance has a minimum for aqueous electrolytes at room temperature but can have a maximum for molten salts and ionic liquids. The transition envelope separating the two situations is found for a modified Poisson-Boltzmann theory and a Poisson-Boltzmann equation corrected for the exclusion volume term. Good agreement is found between simulation and the modified Poisson-Boltzmann theory in the neighborhood of the envelope at the reduced temperature of 0.8, while the exclusion volume corrected Poisson-Boltzmann theory shows correct qualitative trends.
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differential capacitance of the solvent Primitive Model diffuse layer using the inhomogeneous poisson boltzmann theory with an exclusion volume term
Journal of Electroanalytical Chemistry, 2004Co-Authors: S. Lamperski, Christopher W. OuthwaiteAbstract:Abstract The solvent Primitive Model diffuse double layer capacitance is analysed using a Poisson–Boltzmann theory which incorporates the exclusion volume term in the Boltzmann distribution. Unequal ion and solvent sizes are considered and the differential capacitance calculated for 1:1 electrolytes at different electrolyte and solvent concentrations. The unequal ion sizes cause an asymmetry in the capacity curves while the solvent can radically influence its overall shape. At low electrolyte concentrations and small surface charge, the capacitance has a minimum which changes to a maximum as the electrolyte concentration increases. At the higher surface charge densities the capacity curve approaches limiting values, these values depending on the relative counterion size.
Hartmut Löwen - One of the best experts on this subject based on the ideXlab platform.
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Highly asymmetric electrolytes in the Primitive Model: hypernetted chain solution in arbitrary spatial dimensions.
Journal of Computational Chemistry, 2013Co-Authors: Marco Heinen, Elshad Allahyarov, Hartmut LöwenAbstract:The pair-correlation functions for fluid ionic mixtures in arbitrary spatial dimensions are computed in hypernetted chain (HNC) approximation. In the Primitive Model (PM), all ions are approximated as nonoverlapping hyperspheres with Coulomb interactions. Our spectral HNC solver is based on a Fourier-Bessel transform introduced by Talman (J. Comput. Phys. 1978, 29, 35), with logarithmically spaced computational grids. Numeric efficiency for arbitrary spatial dimensions is a commonly exploited virtue of this transform method. Here, we highlight another advantage of logarithmic grids, consisting in efficient sampling of pair-correlation functions for highly asymmetric ionic mixtures. For three-dimensional fluids, ion size and charge-ratios larger than 1000 can be treated, corresponding to hitherto computationally not accessed micrometer-sized colloidal spheres in 1-1 electrolyte. Effective colloidal charge numbers are extracted from our PM results. For moderately large ion size and charge-asymmetries, we present molecular dynamics simulation results that agree well with the approximate HNC pair correlations. © 2013 Wiley Periodicals, Inc.
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highly asymmetric electrolytes in the Primitive Model hypernetted chain solution in arbitrary spatial dimensions
arXiv: Soft Condensed Matter, 2013Co-Authors: Marco Heinen, Elshad Allahyarov, Hartmut LöwenAbstract:The pair-correlation functions for fluid ionic mixtures in arbitrary spatial dimensions are computed in hypernetted chain (HNC) approximation. In the Primitive Model, all ions are approximated as non-overlapping hyperspheres with Coulomb interactions. Our spectral HNC solver is based on a Fourier-Bessel transform introduced by Talman [J. Comput. Phys., 29, 35 (1978)], with logarithmically spaced computational grids. Numeric efficiency for arbitrary spatial dimensions is a commonly exploited virtue of this transform method. Here, we highlight another advantage of logarithmic grids, consisting in efficient sampling of pair-correlation functions for highly asymmetric ionic mixtures. For three-dimensional fluids, ion size- and charge-ratios larger than one thousand can be treated, corresponding to hitherto computationally not accessed micrometer-sized colloidal spheres in 1-1 electrolyte. Effective colloidal charge numbers are extracted from our Primitive Model results. For moderately large ion size- and charge-asymmetries, we present Molecular Dynamics simulation results that agree well with the approximate HNC pair correlations.
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nonmonotonic variation with salt concentration of the second virial coefficient in protein solutions
Physical Review E, 2003Co-Authors: Elshad Allahyarov, Hartmut Löwen, Jeanpierre Hansen, Ard A LouisAbstract:The osmotic virial coefficient B 2 of globular protein solutions is calculated as a function of added salt concentration at fixed pH by computer simulations of the "Primitive Model." The salt and counterions as well as a discrete charge pattern on the protein surface are explicitly incorporated. For parameters roughly corresponding to lysozyme, we find that B 2 first decreases with added salt concentration up to a threshold concentration, then increases to a maximum, and then decreases again upon further raising the ionic strength. Our studies demonstrate that the existence of a discrete charge pattern on the protein surface profoundly influences the effective interactions and that linear and nonlinear Poisson Boltzmann theories fail for large ionic strength. The observed nonmonotonicity of B 2 is compared with experiments. Implications for protein crystallization are discussed.
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attraction between like charged macroions by coulomb depletion
Physical Review Letters, 1998Co-Authors: Elshad Allahyarov, Hartmut Löwen, Irene DamicoAbstract:A novel mechanism for counterion-mediated attraction between like-charged spherical macroions is proposed, which originates from a depletion zone of counterions between nearly touching macroions that is induced by Coulomb interactions. Using computer simulations of the Primitive Model, we show that this depletion effect dominates over the electrostatic contribution in the case of strong Coulomb coupling when all the counterions form a quasi-two-dimensional layer on the spherical macroionic surface. Its range is given by the typical spacing of counterions on the macroion surface.
S Sokolowski - One of the best experts on this subject based on the ideXlab platform.
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restricted Primitive Model for electrolyte solutions in slit like pores with grafted chains microscopic structure thermodynamics of adsorption and electric properties from a density functional approach
Journal of Chemical Physics, 2013Co-Authors: Orest Pizio, S SokolowskiAbstract: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.
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electric double layer capacitance of restricted Primitive Model for an ionic fluid in slit like nanopores a density functional approach
Journal of Chemical Physics, 2012Co-Authors: Orest Pizio, S Sokolowski, Z SokolowskaAbstract:We apply recently developed version of a density functional theory [Z. Wang, L. Liu, and I. Neretnieks, J. Phys.: Condens. Matter 23, 175002 (2011)]10.1088/0953-8984/23/17/175002 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 maxi...
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temperature dependence of the double layer capacitance for the restricted Primitive Model of an electrolyte solution from a density functional approach
Journal of Chemical Physics, 2005Co-Authors: Joanna Reszkozygmunt, Douglas Henderson, S Sokolowski, Dezső BodaAbstract:We apply a different version of the density functional theory, given by Pizio, Patrykiejew, and Sokolowski [J. Chem. Phys. 121, 11957 (2004)], for a nonuniform restricted Primitive Model of an electrolyte solution to evaluate the temperature dependence of the capacitance of an electric double layer. We show that this theory is capable of reproducing the computer simulation data at a quantitative level. In particular, the reversal of the temperature dependence of the capacitance at low temperatures is predicted. This phenomenon has been difficult to predict from theory. Further, this theory also leads to an accurate description of the double layer structure.
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phase behavior of ionic fluids in slitlike pores a density functional approach for the restricted Primitive Model
Journal of Chemical Physics, 2004Co-Authors: Orest Pizio, A Patrykiejew, S SokolowskiAbstract:We present a density functional theory of nonuniform ionic fluids. This theory is based on the application of the electrostatic contribution to the free energy functional arising from mean spherical approximation for a bulk restricted Primitive Model and from the energy route bulk equation of state. In order to employ this functional we define a reference fluid and additional averaged densities, according to the approach introduced by Gillespie, Nonner and Eisenberg [J. Phys.: Condens. Matter 14, 12129 (2002)]. In the case of bulk systems the proposed theory reduces to the mean spherical approximation equation of state, arising from the energy route and thus it predicts the first-order phase transition. We use this theory to investigate the effects of confinement on the liquid–vapor equilibria. Two cases are considered, namely an electrolyte confined to the pore with uncharged walls and with charged walls. The dependence of the capillary evaporation diagrams on the pore width and on the electrostatic pote...
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simulation and density functional study of a simple membrane separating two restricted Primitive Model electrolytes
Journal of Chemical Physics, 1999Co-Authors: Dezső Boda, Douglas Henderson, Richard L Rowley, S SokolowskiAbstract:A simple membrane, supporting charge densities σ1 and σ2=−σ1 on its inner and outer surfaces, is considered. In addition to the electrostatic potential, the membrane interacts with the surrounding fluid by a short range van der Waals-like potential. The fluid beyond the outer surface is a three-component restricted Primitive electrolyte consisting of two cations and one anion. The membrane is impermeable to one of the cations so that the fluid in the membrane and beyond the inner surface is a two-component restricted Primitive electrolyte. We use Monte Carlo simulations and density functional theory to study the density profiles of the electrolyte and the charge-electrostatic potential relationship for the membrane surfaces. Even though σ2=−σ1, the potentials on the membrane surfaces are not equal and opposite. We also study a membrane consisting of a single charged plane. For both Models, the density functional results are in good agreement with the simulations.
L B Bhuiyan - One of the best experts on this subject based on the ideXlab platform.
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the point ion modified poisson boltzmann theory for a planar electric double layer with different permittivities for the electrode inner layer and diffuse layer
Molecular Physics, 2014Co-Authors: C. W. Outhwaite, L B BhuiyanAbstract:The planar electric double layer is Modelled by an electrode, inner layer and diffuse layer whose constant permittivities differ. A point ion modified Poisson–Boltzmann analysis is made of the Model with the ions in the diffuse layer having a distance of closest approach to the electrode, which is greater than the inner layer thickness and mimics the ion radius of a Primitive Model electrolyte. Comparisons are made with existing Monte Carlo simulations for uncharged and charged electrodes. For 1:1 and 2:1 electrolytes with a charged electrode, the modified Poisson–Boltzmann theory successfully predicts the singlet ion normalised density functions and the mean electrostatic potential. With the uncharged electrode, the neglect of ion size is more critical and the theoretical predictions are now poor at the higher concentrations.
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the electric double layer differential capacitance at and near zero surface charge for a restricted Primitive Model electrolyte
Journal of Physical Chemistry B, 2009Co-Authors: S. Lamperski, Christopher W. Outhwaite, L B BhuiyanAbstract:The behavior of the differential capacitance of a planar electric double layer containing a restricted Primitive Model electrolyte in the neighborhood of zero surface charge is investigated by theory and simulation. Previous work has demonstrated that at zero surface charge the differential capacitance has a minimum for aqueous electrolytes at room temperature but can have a maximum for molten salts and ionic liquids. The transition envelope separating the two situations is found for a modified Poisson-Boltzmann theory and a Poisson-Boltzmann equation corrected for the exclusion volume term. Good agreement is found between simulation and the modified Poisson-Boltzmann theory in the neighborhood of the envelope at the reduced temperature of 0.8, while the exclusion volume corrected Poisson-Boltzmann theory shows correct qualitative trends.
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some simulation and modified poisson boltzmann theory results for the contact values of an electrolyte near a charged electrode
Journal of Electroanalytical Chemistry, 2007Co-Authors: L B Bhuiyan, C. W. OuthwaiteAbstract:Abstract Since the development of a contact value theorem by Henderson et al. it has been known that the prediction of the venerable Gouy–Chapman (GC) theory for the contact value of the density profile of an electrolyte near an electrode is incorrect. The more recent semi-empirical work of Fawcett and Henderson and the simulations of Boda and Henderson have shown that the contact value of the charge profile at low electrode charge is also given incorrectly by the GC theory, at least for a binary symmetric restricted Primitive Model electrolyte. In the present study we examine the contact values of the profiles of the double layer formed by the electrolyte species in a binary symmetric restricted Primitive Model electrolyte as a function of the electrode charge by means of simulation. It is difficult to extract detailed information from simulation values of the density and charge profiles at large electrode charge because the contact values of these profiles are dominated by the large quadratic term in the electrode charge. However, we find from our simulations for a fairly wide range of concentrations and electrode charges, that the product of the counterion and coion profiles is a sensitive probe with which to study the double layer because it is a direct test of the basis of the GC approximation that the counterion and coion profiles are exponentials of ± zeψ ( x )/ kT and so have a product that is identically one. We find that this product is not one or even a constant as the electrode charge is varied and, thus, the GC contact values do not agree even qualitatively with the simulation results. In contrast, the modified Poisson–Boltzmann theory is quite successful in accounting for the behavior of this product.