Asymmetric Salts and Polyelectrolyte on Charge Inversion of a Spherical/Rod Macroion: Electrophoresis by Molecular Dynamics Simulations

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Abstract
The charge inversion phenomenon is studied by molecular dynamics simulations, focusing on size and valence asymmetric salts, polyelectrolyte counterions, and a threshold of surface charge density for charge inversion. The reversed electrophoretic mobility increases with the ratio of coion to counterion radii, while it decreases with the ratio of coion to counterion valences. The monovalent salt enhances charge inversion of a strongly charged macroion at small ionic strength, but it reduces reversed mobility otherwise. The surface charge density threshold becomes less for a cylindrical macroion with polymer (polyelectrolyte) counterions than for a spherical macroion and isolated counterions. The mobility reversal for the DNA may result from the charge inversion combined with the hydrophobic attractions or the mechanical twining of polyelectrolyte around the rod axis.

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