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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1480-1486 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of a model colloidal suspension in the vicinity of a charged wall is studied in the framework of the Derjaguin–Landau–Verwey–Overbeek interaction potential and the hypernetted-chain approximation. Here we consider the case of dilute suspension of highly charged macroparticles interacting with weakly repulsive, neutral, and attractive walls. As the wall–particle electrostatic interactions become successively less repulsive, the formation of a monolayer of colloidal particles, strongly adsorbed onto the surface, is predicted by our results. This monolayer of electrostatically confined particles mimic the effect of an effective surface charge distribution adjacent to the wall which, together with the bare wall surface charge, induces on the other, nonconfined, colloidal particles the same local-concentration profile as that in front of a highly charged and repulsive wall.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2109-2115 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The idea of the rescaled mean spherical approximation (RMSA) is extended to describe the local concentration profile of a suspension of highly charged particles near a charged wall. The predictions of this essentially analytic approximation for the wall–particle correlations, under conditions that the "rescaling'' is needed, are in excellent quantitative agreement with those of the HNC approximation. It is found that the structure of the inhomogeneous suspension (the magnitude and relative spacing of the oscillations in the local macroparticle concentration, as a function of the distance from the wall) only depends on the bulk properties of the suspension. The charge density of the wall only contributes to determine the displacement of this local structure away from the wall.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2344-2350 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the Ornstein–Zernike equations together with the extended Zerah–Hansen approach, described in a previous paper [J. Chem. Phys. 109, 11074 (1998)], to determine the microstructure of a colloidal suspension at finite concentrations. Using these results as an input, the effective pair potential between two colloidal particles is also calculated following the general approach described in that paper. It is found that, for sufficiently large concentrations, this effective potential develops an attractive well with a minimum located at a distance of almost four macroparticle diameters. It is also shown that this attraction is generated by the inversion of the sign of the effective charged distribution surrounding each macroparticle involved in the electrostatic component of the effective pair potential. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 507-517 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study binary polyelectrolytes in the melt state and in concentrated solutions using the random phase approximation (RPA). We compute the thermodynamics and electrostatics of chemically linked polyelectrolytes chains into block copolymer molecules (copolyelectrolytes). Polyelectrolytes blends and copolyelectrolytes in the presence of free ions have Debye–Hückel-type effective monomer–monomer interactions, even when the polymer chains are not charged. Copolyelectrolyte of chemically linked chains of opposite charge in the absence of counterions, have ion–ion effective interactions characteristic of a dielectric medium, contrary to the case of polyelectrolyte blends where these effective interactions are Debye–Hückel type, even on the absence of free ions. The dielectric constant in such a diblock copolymer melt is proportional to the square of the degree of polymerization Np. In the reference state (without interactions) RPA assumes random walk statistics, which are nearly unperturbed in the dielectric; we find the scaling of the end-to-end vector square of a chain in the dielectric. We also discuss the physics of other copolyelectrolytes (polyampholytes).
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2006-2011 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of a model two-component colloidal mixture in the vicinity of a charged wall is studied in the framework of the Derjaguin–Landau–Verweg–Overbeek potential and the hypernetted-chain approximation for the particle–particle and wall–particle direct correlation functions as the closure for the bulk and wall–particle Ornstein–Zernike equations. It is found that for strongly repulsive walls the structure of the inhomogeneous mixture near the wall only depends on the bulk parameters. For neutral and attractive walls, a monolayer of colloidal particles adjacent to the wall is formed. Depending on the charge asymmetry between the two colloidal species, the composition of this monolayer indicates a preferential electrostatic adsorption of the more highly charged species. For large charge asymmetry between the two species, a distinct segregation effect is predicted.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8337-8345 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present a simple theoretical scheme to calculate the inhomogeneous structure of an aqueous monodisperse suspension of highly charged spherical particles confined between two parallel charged walls. The theoretical model is based on the Derjaguin–Landau–Verwey–Overbeek level of description for the particle–particle and wall–particle interactions. The main features of the theoretically predicted local-concentration profile are found to be in good agreement with our Monte Carlo simulations for the same model. In particular, in the limiting case of large wall-to-wall separation, the predictions of previous work, concerning the structure of a suspension in the neighborhood of a highly repulsive wall, are found to agree with our simulation results.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5949-5955 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work we present an extension of the Rogers–Young approximation to the determination of the concentration profile of a colloidal suspension of charged particles in front of a flat highly repulsive wall. The thermodynamic consistency condition used here is the matching of the force per unit area exerted by the macroparticles over the wall, with the corresponding osmotic pressure in the bulk determined from the virial equation. The suspension is described as a one-component fluid, constituted by the macroparticles, with all the relevant interactions modeled by the Derjaguin–Landau–Verwey–Overbeek effective potentials. The predictions of this new scheme are compared with Monte Carlo computer simulation data. The main conclusion is that the Rogers–Young approximation is in closer agreement with the simulation data than the hypernetted chain and rescaled mean approximations presented in previous works. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 11074-11084 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general formalism for ionic fluids is presented. We report general and exact expressions for the distribution functions which directly satisfy the Stillinger–Lovett moment conditions. General and exact expressions are also provided for the effective pair potentials among charged colloidal particles. These general expressions are a direct consequence of the multicomponent Ornstein–Zernike (OZ) equations and the asymptotic behavior of the direct correlation functions in charged systems. The effective pair potentials show two distinct parts: short-ranged and electrostatic. For the primitive model (PM) with pointlike small ions the electrostatic component is reduced, for sufficiently large distances, to a screened Coulomb potential with renormalized charges. The general expression of the effective electrostatic interaction gives a clear insight of the specific conditions of validity of the Derjaguin–Landau–Verwey–Overbeek (DLVO) model and of the possible directions in which this model may be improved. We also present results for the PM with pointlike small ions obtained from an implementation of the Zerah–Hansen (ZH) approximation complemented with a new minimization criterion. These results are compared with experimental data to test the accuracy of the predictions of the ZH scheme against those obtained from the DLVO model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3145-3157 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study ion condensation in salt-free dilute solutions of polyelectrolyte chains of different fractal geometries, from random walks to rigid rods. In finite size chains with a discrete charge distribution, ion condensation is only observed in multiple chain systems. A thermodynamic analysis of ion condensation with linearized interactions among the condensed counterions and the monomers leads to rigid rod lowest free energy conformations, regardless of the values of the valency of the monomers (zm), the negative value of the ratio of the valency of the counterions to the valency of the monomers (Pz), and the ratio of the Bjerrum length (lB) to the distance between charges along the polyion (b). As z2mPzlB/b increases, however, the fraction of condensed counterions increases and the polyion concentration at which ion condensation appears decreases. Above this critical polyion concentration, ion condensation is observed even when lB/b〈1/z2mPz. When correlations are included, representing the tendency of the condensed counterions to be surrounded by opposite sign charges, the chain conformation is strongly dependent on the valency of the counterions and lB/b. For large valency counterions and/or lB/b values, collapsed finite chains have lower free energies than rigid rods. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5747-5755 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper an extension of the rescaled mean spherical approximation is presented, which describes the local concentration profile of a colloidal suspension of charged particles confined between two parallel highly repulsive walls. The predictions of this scheme are in good quantitative agreement with those of the hypernetted-chain approximation. It is found that, for a given set of values of the bulk parameters, the structure of the concentration profile only depends on the value of the minimum of the external potential.
    Type of Medium: Electronic Resource
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