Effects of asymmetric salt and a cylindrical macroion on charge inversion: Electrophoresis by molecular dynamics simulations

Abstract

The charge inversion phenomenon is studied by molecular dynamics simulations, focusing on size and valence asymmetric salts, and a threshold of surface charge density for charge inversion. The charge inversion criteria by the electrophoretic mobility and the radial distribution functions of ions coincide except around the charge inversion threshold. The reversed electrophoretic mobility increases with the ratio of coion to counterion radii a − /a + , while it decreases with the ratio of coion to counterion valences Z − /Z + . The monovalent salt enhances charge inversion of a strongly charged macroion at small salt ionic strength, while it reduces reversed mobility otherwise. A cylindrical macroion is more persistent to monovalent salt than a spherical macroion of the same radius and surface charge density.

Simulation of charge reversal in salty environments: Giant overcharging?

“…Simulations have confirmed the phenomenon of overcharging [16,17,18,19,20], and they are mostly consistent with the OCP theories in the strong-coupling regime, which is close to the Wigner-crystal (T = 0) limit. A notable exception is the work by Messina et al [21], which shows that overcharging is also possible in situations that are very far from the strong coupling limit.…”

“…In the following, we define the effective charge Z eff of the colloid as the maximum of the integrated charge distribution Z int . This definition of the effective charge corresponds to the static model of Tanaka and Grosberg [18,20].…”

“…Not many simulations have been performed of that situation, however, all of them seem to support the ex-perimental finding, that the amount of reversed charge decreases with increasing salt content. Tanaka and Grosberg have performed simulations of the electrophoresis of a colloid in salt solution in a regime of very high surface charge [20]. Martin-Molina [24,25] et al simulate the overcharging at a planar wall in salty environment under more realistic conditions, which should be valid in the limit of large colloids.…”

Multiple-image treatment of induced charges in Monte Carlo simulations of electrolytes near a spherical dielectric interface

“…The traditional PB theory fails to describe it, and thus the explanation of charge inversion has motivated a lot of theoretical and computational investigation as it could be relevant in many physical and biological problems such as the like-charge attraction between DNA rods [9]. A number of theories [10], such as integral equations, field theoretic calculations, and density functional theory, have been developed to describe this phenomenon, as well as molecular dynamics and MC simulations [21,[47][48][49][50] which confirm the theoretical predictions. In the simulations of this paper, we aimed to verify the performance of the method of images through simulating this phenomenon and to study the effect of the image charges of the overcharging by considering discrete interfacial charges in Sec.…”

The mixture effect on ionic selectivity and permeability of nanotubes

“…25 The underlying mechanism of the charge inversion has been studied with various approaches including analytical theories such as one-component plasma (OCP) theory, 27 Monte Carlo (MC) simulations, 28 and molecular dynamics (MD) simulations. 29 The other is the anomalous mole fraction effect (AMFE), i.e., the conductance of the mixture of two salts through the nanopore is less than that of the single salt at the same concentration. This effect was rst discovered in protein ion channels with classic mole fraction experiments 30 and was suggested to originate from multiple-ion single-le transport based on kinetic theory.…”