Charged surface in salty water with multivalent ions: Giant inversion of charge

TL;DR

This paper investigates how multivalent ions in salty water can cause a macroion's charge to invert and even surpass its original magnitude, with implications for electrophoresis.

Contribution

It reveals the mechanism of charge inversion due to correlated multivalent ions and demonstrates the possibility of giant charge inversion in salty solutions.

Findings

Charge inversion occurs at moderate multivalent ion concentrations.

High salt concentration can lead to charge inversion exceeding the macroion's bare charge.

Giant charge inversion is observable in electrophoretic experiments.

Abstract

Screening of a strongly charged macroion by oppositely charged colloidal particles, micelles, or short polyelectrolytes is considered. Due to strong lateral repulsion such multivalent counterions form a strongly correlated liquid at the surface of the macroion. This liquid provides correlation induced attraction of multivalent counterions to the macroion surface. As a result even a moderate concentration of multivalent counterions in the solution inverts the sign of the net macroion charge. We show that at high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one. This giant inversion of charge can be observed in electrophoresis.