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

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 electrode), where phenomena as charge reversal, charge inversion and overcharging have been shown to be relevant. However, experimental studies at finite volume fraction exhibit interesting phenomenology which imply very long-range correlations. In this paper we apply an integral equation theory to a simple model for a charged macroions suspensions, 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

Very long-range attractive and repulsive forces in model colloidal dispersions

“…While our r ca results confirm the existence of a long-range macroions attraction, and have a good qualitative agreement with some experimental data, we wish to emphasize the relevance of the truly very long range of the oscillatory macroionmacroion radial distribution function and force, which may have relevant consequences in several soft condensed matter and biological systems [56,57].…”

“…A number of sequential charge inversions is observed, indicating the change of direction of the electrical field, E M (r). The locations of the maxima and minima of the charge density in the fluid are closely related to the macroions' size, volume fraction, surface charge, and location, and show interesting new surface phenomena [56,57]. However, in this article we addresses only to the foundations, nature and range of the forces among charged macroions.…”