Phase Separation of Polyelectrolytes: The Effect of Charge Regulation

TL;DR

This paper investigates how charge regulation mechanisms influence the phase separation behavior of oppositely charged polyelectrolytes, revealing that charge differences between phases are affected by CR parameters and secondary effects.

Contribution

It introduces and analyzes two charge regulation models (HCR and ACR) and their impact on phase diagrams and charge distribution in polyelectrolyte coacervation.

Findings

Polymers in the condensed phase are more charged than in the dilute phase.

Secondary CR effects influence phase volume fractions.

Charge differences can change nonmonotonically with CR parameters.

Abstract

Complex coacervation, known as the liquid-liquid phase separation of solutions with oppositely charged polyelectrolytes, has attracted substantial interest in recent years. We study the effect of the charge regulation (CR) mechanism on the complex coacervation by including short-range interactions between the charged sites on the polymer chains as well as an association-dissociation energy parameter in the CR mechanism. We investigate the phase diagrams of two CR models: (i) the hopping CR model (HCR) and (ii) the asymmetric CR model (ACR). It is shown that during the phase separation that the polymers in the condensed phase are more charged than those in the dilute phase, in accordance with Le Chatelier's principle. In addition, secondary CR effects also influence the change in the volume fraction of the two phases. The latter can cause the charge difference between the two phases to change nonmonotonically as a function of the CR parameters.