Volume Phase Transition of Polyelectrolyte Gels: Effects of Ionic Size

TL;DR

This paper extends classical theory of polyelectrolyte gels to include finite ionic size, revealing how ionic volume influences volume transition behavior, phase diagrams, and salt-induced collapse, offering insights for tuning gel swelling.

Contribution

It introduces a theoretical extension accounting for ionic size effects on polyelectrolyte gel volume transitions and phase behavior.

Findings

Discontinuous volume transition becomes continuous with larger ions.

Salt concentration and ionic size affect gel collapse and phase diagrams.

Swelling behavior can be tuned by ionic size of added salts.

Abstract

Although the volume transition of the polyelectrolyte gel has been studied for decades, little research on the effects of size of the mobile ions has been conducted. In the present paper, Tanaka classical theory of polyelectrolyte gel is extended to the cases of mobile ions of finite volume. In the salt free limit, the theoretical results show that the discontinuous volume transition of the polyelectrolyte gel will become a continuous one with an increase of the counter-ionic size. An increase in salt concentration can also make the polyelectrolyte gel in poor solvent collapse. Poorer solvent is needed to trigger the salt-induced collapse in polyelectrolyte gel with larger mobile ions than that with smaller ones. The effects of ionic size on the critical points and phase diagram of the volume transition are also discussed. The theoretical results suggest that the swelling behavior of polyelectrolyte gel might be tuned with salt of different volumes.