Giant charge inversion of a macroion due to multivalent counterions and monovalent coions: Molecular dynamics study

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 multivalent counterions similar to Bjerrum pairing is the major factor restricting 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 ∼ ζ 1/2 when ζ < 1 and crosses over to ∼ ζ for ζ > 1, where ζ = (A0/rs) 2 , rs is the Debye screening length in the electrolyte and A0 is the distance between adsorbed counterions under neutralizing conditions. These findings are consistent with the theory of "giant charge inversion" [Phys. Rev.Lett., 85, 1568].

Mesoscale modelling of polyelectrolyteelectrophoresis

“…The hydrodynamic screening length depends on the ion concentration in the vicinity of the chain. This relation between the ion density and the hydrodynamic screening length was previously suggested by different authors [31,32].…”

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

“…More recently, it also attracted a significant attention of physicists [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Charge inversion is now understood to be the generic phenomenon that occurs in strongly correlated charged systems.…”

“…In our previous papers, we adopted the static [12] and dynamical [13] models to study charge inversion of the spherical macroion by molecular dynamics simulations. In the former study where a macroion was immovable, the static quantities were obtained including the radial distribution profiles of counterions and coions moving in the Langevin thermostat.…”

Size correlations in colloidal suspensions

“…Namely, instead of charge reduction due to the shielding, it is possible to observe a charge reversal due to overscreening. The charge inversion phenomena becomes enhanced with the increasing concentrations of multivalent salt [12] [13]. Unfortunately the actual mechanism of this overcharging is not clear.…”

“…Recent simulations suggest that the attraction between like charges might be related to the mechanism that induces overcharging [11]- [13]. Therefore, understanding the mechanism that leads to overcharging will shed some light in the appearance of attraction between like-charged polyions.…”