The effect of ionic size on polyion-small ion distributions in a
cylindrical double layer
Authors: C.N.Patra (Theoretical Chemistry Section, RC & CD Division, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085, India; Department of Materials Science and Engineering University of Utah 122 S. Central Campus Drive Salt Lake City, Utah 84112-0560) , L.B.Bhuiyan (Laboratory of Theoretical Physics, Department of Physics, Box 23343, University of Puerto Rico, San Juan, Puerto Rico 00931-3343)
The structure of an electrolyte surrounding an isolated, cylindrical polyion - the cylindrical double layer - is studied using a density functional approach and the modified Poisson Boltzmann theory. The polyion is modelled as an infinitely long, rigid, and impenetrable charged cylinder, while the electrolyte consists of rigid ions moving in a dielectric continuum. The results for the zeta potential, polyion-small ion distribution, and the mean electrostatic potential are obtained for a wide range of physical conditions including three different ionic diameters of 2, 3, and 4·10-10 m. The zeta potentials show a maximum or a minimum with respect to the polyion surface charge density for a divalent counterion. The polyion-ion distributions and the mean electrostatic potential profiles show considerable variations with the concentration of the electrolyte, the valency of the ions constituting the electrolyte, and the ionic size. The theories are seen to be generally consistent with each other overall, and are capable of predicting the charge inversion phenomenon - a feature, which is completely absent in the classical Poisson-Boltzmann theory. Moreover, the theories reproduce well some Monte Carlo results (for ion distributions) from the literature.
cylindrical double layer, structure, density functional
theory, modified Poisson-Boltzmann
PACS: 82.70.Dd; 64.10.+h
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