Electric double layer for a size-asymmetric electrolyte around a spherical colloid

We have studied the structure of a size-asymmetric electrolyte on charged colloids by a density functional perturbation theory. The hard-sphere contribution has been approximated as the direct pair correlation function with the coupling parameter, whereas the electronic contribution has been approxi...

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Bibliographic Details
Published in:The Journal of chemical physics 2014-04, Vol.140 (15)
Main Authors: Kim, Eun-Young, Kim, Soon-Chul
Format: Article
Language:English
Subjects:
Approximation
APPROXIMATIONS
Asymmetry
Bulk density
CHARGE DENSITY
Charge reversal
COLLOIDS
Computer simulation
COMPUTERIZED SIMULATION
DENSITY
DENSITY FUNCTIONAL METHOD
Electric double layer
ELECTROLYTES
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
Mathematical analysis
PERTURBATION THEORY
Physics
Surface charge
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Summary:We have studied the structure of a size-asymmetric electrolyte on charged colloids by a density functional perturbation theory. The hard-sphere contribution has been approximated as the direct pair correlation function with the coupling parameter, whereas the electronic contribution has been approximated as the mean-spherical approximation in the bulk phase. The calculated results for the ionic density distributions and mean electrostatic potentials are in very good agreement with the computer simulations over a wide range of colloid sizes and electrolyte concentrations. The present theory provides better structural results than the hypernetted-chain equation based on the mean spherical approximation. We have confirmed that the overcharging appears when the counterions are larger than the coions. The overcharging disappears everywhere when the electrostatic repulsion becomes strong enough, while the charge reversal is observed when the coions are larger than the counterions, and the reversal effect appears for a size-asymmetric electrolyte at high surface charge densities. The charge reversal occurs even for the point of zero charge, mainly due to the depletion force between two ions. The present theory is able to provide interesting insights about the charge reversal and overcharging phenomena occurring at the interface.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.4871499