Polyelectrolytes Adsorption: Chemical and Electrostatic Interactions

TL;DR

This study uses mean-field theory to analyze polyelectrolyte adsorption on charged surfaces, revealing how salt concentration and surface chemistry influence overcharging and charge inversion, with implications for multilayer assembly.

Contribution

It provides new scaling laws and detailed analysis of overcharging behavior for different surface types, enhancing understanding of polyelectrolyte-surface interactions.

Findings

Overcharging is significant on chemically attractive surfaces at high salt.

Full charge inversion is not achieved at thermodynamic equilibrium.

Overcharging scales linearly with surface charge but remains small.

Abstract

Mean-field theory is used to model polyelectrolyte adsorption and the possibility of overcompensation of charged surfaces. For charged surfaces that are also chemically attractive, the overcharging is large in high salt conditions, amounting to 20-40% of the bare surface charge. However, full charge inversion is not obtained in thermodynamical equilibrium for physical values of the parameters. The overcharging increases with addition of salt, but does not have a simple scaling form with the bare surface charge. Our results indicate that more evolved explanation is needed in order to understand polyelectrolyte multilayer built-up. For strong polymer-repulsive surfaces, we derive simple scaling laws for the polyelectrolyte adsorption and overcharging. We show that the overcharging scales linearly with the bare surface charge, but its magnitude is very small in comparison to the surface charge. In contrast with the attractive surface, here the overcharging is found to decrease substantially with addition of salt. In the intermediate range of weak repulsive surfaces, the behavior with addition of salt crosses over from increasing overcharging (at low ionic strength) to decreasing one (at high ionic strength). Our results for all types of surfaces are supported by full numerical solutions of the mean-field equations.