Long-range overcharging and long-range charge reversal in model colloidal dispersions

TL;DR

This paper demonstrates the existence of long-range overcharging and charge reversal phenomena in colloidal dispersions at finite volume fractions, revealing correlations at large distances that differ from classical short-range effects.

Contribution

It introduces the concepts of long-range overcharging and charge reversal in colloidal suspensions at finite volume fractions, supported by integral equation theory, simulations, and experimental consistency.

Findings

Long-range overcharging occurs at finite macroion volume fractions.

Charge reversal effects increase with distance from the macroion.

Results are consistent with experimental and simulation data.

Abstract

Most theoretical and simulation studies on charged particles suspensions are at infinite dilution conditions. Hence these studies have been focused on the electrolyte structure around an isolated central particle (or elctrode), where phenomena as charge reversal, charge inversion and overcharging have been shown to be relevant. However, experimental studiesat finite volume fraction exhibit interesting phenomenology which imply very long-range correlations. Inthis paper we apply an integral equation theory to a simple model for a charged macroions suspension, at finite volume fraction, and find two new effects of long-range overcharging and long-range charge reversal. These new effects are different from the classical overcharging and charge reversal in that they occur at finite macroion's volume fraction, far away from the central macroion, are much more intense, and increase, not decrease, as a function of the distance to the central particle, which is indicative of correlations at large separations. We find our results to be qualitative consistent with existing experimental results, and Monte Carlo simulations.