Complexation of oppositely charged polyelectrolytes: effect of ion pair formation

TL;DR

This paper presents a theoretical study of polyelectrolyte complexation, emphasizing the role of ion pair formation and electrostatic interactions, and analyzes stability conditions with added salt.

Contribution

It introduces a self-consistent model incorporating thermoreversible ion pairing and electrostatics within the Random Phase Approximation for polyelectrolyte complexation.

Findings

Ion pair formation significantly influences complex stability.

Electrostatic and van der Waals forces are key in driving complexation.

Conditions for stable complexes with salt are characterized.

Abstract

Complexation in symmetric solutions of oppositely charged polyelectrolytes is studied theoretically. We include polyion crosslinking due to formation of thermoreversible ionic pairs. The electrostatic free energy is calculated within the Random Phase Approximation taking into account the structure of thermoreversible polyion clusters. The degree of ion association is obtained self-consistently from a modified law of mass action, which includes long-range electrostatic contributions. We analyze the relative importance of the three complexation driving forces: long-range electrostatics, ion association and van der Waals attraction. The conditions on the parameters of the system that ensure stability of the complex with addition of salt are determined.