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Forces between like-charged walls immersed in electrolyte solution Otto, Frank
Abstract
The effects of a molecular solvent on the forces between two infinite like-charged walls immersed in aqueous electrolyte solution are investigated. The solution models are chosen such that the numerical solution of accurate anisotropic integral equation theories is possible, and the anisotropic hypernetted-chain (AHNC) approximation is used in the present calculations. The resulting average particle densities and the pair correlation functions are used to analyze the force acting between the walls in detail. Mixtures of neutral hard-sphere solvent particles and counterions are employed to investigate the influence of the finite size of the solvent molecules. At wall separations of a few solvent diameters, even at relatively high surface charge and moderate solvent density, the ionic contribution to the force tends to be dominated by the hard-core or packing component. If the ions and solvent particles are of equal size, then the net pressure between the walls can be reasonably well approximated by adding the pressures of pure one-component ionic and solvent systems. However, if the ion and solvent diameters are significantly different, the pressure curve is more complex, and the hard-core component must be evaluated for a mixture of neutral hard spheres. The interaction of the walls is also investigated at the McMillan-Mayer (MM) level of description. In these models, the solvent is not represented by discrete particles but exerts its influence through solvent-averaged ion-ion potentials of mean force which serve as effective potentials. The approximations involved in applying MM theory to the inhomogeneous slit system are discussed. The wall-wall interactions obtained can differ dramatically from the primitive model (dielectric continuum solvent) case. Most interestingly, at the MM level, the force between like-charged walls at small separations and with realistic surface charges can be attractive for monovalent counterions, which is due to solvent effects on the effective counterion-counterion interaction. Several ion-ion potentials of mean force for "realistic" models for Na+ and CI- in water are available in the literature. We find that the forces strongly depend on the model employed and different models for the same ion can give qualitatively different results. To construct a self-consistent model, ion-wall potentials of mean force must also be considered. Typical model ion-wall potentials show an additional counterion attraction towards the walls. Incorporation of these wall potentials yields an overall increase of the attraction between the walls. The possible relevance of our observations in the interpretation of experimental force measurements is briefly discussed.
Item Metadata
Title |
Forces between like-charged walls immersed in electrolyte solution
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2000
|
Description |
The effects of a molecular solvent on the forces between two infinite like-charged walls
immersed in aqueous electrolyte solution are investigated. The solution models are chosen
such that the numerical solution of accurate anisotropic integral equation theories
is possible, and the anisotropic hypernetted-chain (AHNC) approximation is used in the
present calculations. The resulting average particle densities and the pair correlation
functions are used to analyze the force acting between the walls in detail. Mixtures of
neutral hard-sphere solvent particles and counterions are employed to investigate the
influence of the finite size of the solvent molecules. At wall separations of a few solvent
diameters, even at relatively high surface charge and moderate solvent density, the ionic
contribution to the force tends to be dominated by the hard-core or packing component.
If the ions and solvent particles are of equal size, then the net pressure between the walls
can be reasonably well approximated by adding the pressures of pure one-component ionic
and solvent systems. However, if the ion and solvent diameters are significantly different,
the pressure curve is more complex, and the hard-core component must be evaluated
for a mixture of neutral hard spheres. The interaction of the walls is also investigated
at the McMillan-Mayer (MM) level of description. In these models, the solvent is not
represented by discrete particles but exerts its influence through solvent-averaged ion-ion
potentials of mean force which serve as effective potentials. The approximations involved
in applying MM theory to the inhomogeneous slit system are discussed. The wall-wall
interactions obtained can differ dramatically from the primitive model (dielectric continuum
solvent) case. Most interestingly, at the MM level, the force between like-charged
walls at small separations and with realistic surface charges can be attractive for monovalent
counterions, which is due to solvent effects on the effective counterion-counterion
interaction. Several ion-ion potentials of mean force for "realistic" models for Na+ and
CI- in water are available in the literature. We find that the forces strongly depend on
the model employed and different models for the same ion can give qualitatively different
results. To construct a self-consistent model, ion-wall potentials of mean force must also
be considered. Typical model ion-wall potentials show an additional counterion attraction
towards the walls. Incorporation of these wall potentials yields an overall increase
of the attraction between the walls. The possible relevance of our observations in the
interpretation of experimental force measurements is briefly discussed.
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Extent |
8653171 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-07-27
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0061490
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2000-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.