Effective macroion charge and stability of highly asymmetric electrolytes at various salt conditions

TL;DR

This study investigates how salt concentration affects macroion charge and stability in asymmetric electrolytes, revealing charge inversion and aggregation phenomena through Monte Carlo simulations.

Contribution

It provides new insights into the electrostatic mechanisms behind macroion charge inversion and aggregation at various salt levels using primitive model simulations.

Findings

Macroion effective charge decreases at low salt due to counterion adsorption.

Overcharging occurs at high salt, reversing macroion charge.

Aggregation happens near the macroion isoelectric point.

Abstract

We study electrostatic mechanisms of destabilization of highly asymmetric electrolytes. For this purpose, we perform primitive model Monte Carlo simulations of charged macroions immersed in multivalent salt solution. At low salt concentration, the macroion effective charge is reduced due to multivalent counterion adsorption. At high salt concentrations, the macroions become overcharged so that their apparent charge has the opposite sign to the stoichiometric one. The inverted charge is growing up to a saturation value upon further increasing the salinity. The system remains stable at low as well as at very high salt concentrations. In the intermediate region, close to the macroion isoelectric point, we observe macroion aggregation. The obtained phase behaviour closely resembles polyelectrolyte-induced instability of colloidal dispersions.