Polyelectrolytes in the presence of multivalent ions: gelation versus segregation

TL;DR

This paper investigates how multivalent ions influence the behavior of polyelectrolyte solutions, revealing a balance between gelation and segregation driven by electrostatic interactions and proposing a modified theoretical approach.

Contribution

It introduces a modified Debye-Huckel model to analyze the competition between gelation and segregation in polyelectrolyte solutions with multivalent ions.

Findings

Strong short-range attractions induce gelation, which is suppressed by long-range electrostatic correlations.

Highly dilute solutions tend to undergo macroscopic segregation.

Gels can form in semidilute solutions when specific length scales exceed ion size.

Abstract

We analyze solutions of strongly charged chains bridged by linkers such as multivalent ions. The gelation induced by the strong short range electrostatic attractions is dramatically suppressed by the long range electrostatic correlations due to the charge along the uncrosslinked monomers and ions. A modified Debye-Huckel approach of crosslinked clusters of charged chains is used to determined the mean field gelation transition self-consistently. Highly dilute polyelectrolyte solutions tend to segregate macroscopically. Semidilute solutions can form gels if the Bjerrum length $l_B$ and the distance between neighboring charged monomers along the chain $b$ are both greater than the ion size $a$.