Effects of strongly selective additives on volume phase transition in gels

TL;DR

This study explores how strongly selective additives influence volume phase transitions in gels, revealing that such additives can suppress or induce transitions by altering internal and external concentrations.

Contribution

It introduces a simplified theoretical model explaining the effects of strongly selective additives on gel volume transitions, including control and suppression of discontinuous transitions.

Findings

Strongly selective additives cause gels to shrink with increasing additive concentration.

Adding poor additives can eliminate discontinuous volume phase transitions.

A second volume phase transition can occur far from the original transition point.

Abstract

We investigate volume phase transition in gels immersed in mixture solvents, on the basis of a three-component Flory-Rehner theory. When the selectivity of the minority solvent component to the polymer network is strong, the gel tends to shrink with an increasing concentration of the additive, regardless of whether it is good or poor. This behavior originates from the difference of the additive concentration between inside and outside the gel. We also found the gap of the gel volume at the transition point can be controlled by adding the strongly selective solutes. By dissolving a strongly poor additive, for instance, the discontinuous volume phase transition can be extinguished. Furthermore, we observed that another volume phase trasition occurs far from the original transition point. These behaviors can be well explained by a simplified theory neglecting the non-linearity of the additive concentration.