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Author(s):
M. Tanaka and A. Yu Grosberg
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Title:
Giant Charge Inversion of a Macroion Due to Multivalent Counterions and Monovalent Coions: Molecular Dynamics Study
Date of publication:
Jan. 2001
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Key words:
Nonlinear Debye screening, Coulomb coupling parameter, multivalent ions, condensation.
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Abstract:
We report molecular dynamics simulation of the (overall neutral) system consisting of an immobile macroion surrounded by the electrolyte of multivalent counterions and monovalent coions. As expected theoretically, counterions adsorb on the macroion surface in the amount much exceeding neutralization requirement, thus effectively inverting the sign of the macroion charge. We find two conditions necessary for charge inversion, namely, counterions must be multivalently charged and Coulomb interactions must be strong enough compared to thermal energy. On the other hand, coion condensation on the macroion suppresses the amount of charge inversion.Depending on parameters, we observe inverted charge up to about 200% the original charge of the macroion in absolute value. The inverted charge scales as ~xi^{1/2} when xi < 1 and crosses over to ~ xi for xi > 1, where xi = (R/gamma_s )^2, R and gamma_s being the distance between the macroion and adsorbed counterions and the Debye screening length in the electrolyte under neutralizing conditions, respectively. These findings are highly consistent with the theory of "giant charge inversion" [Phys.Rev.Lett.,85, 1568 (2000)].
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