Viscoelastic Phase Separation Model for Ternary Polymer Solutions

TL;DR

This paper introduces a new model for viscoelastic phase separation in ternary polymer solutions, revealing network formation mechanisms and solvent dynamics crucial for membrane manufacturing.

Contribution

The paper develops a novel viscoelastic phase separation model specifically for ternary polymer solutions, extending understanding beyond binary systems.

Findings

Network-like structures form during phase separation in ternary solutions.

Solvent moves freely between phases despite similar affinity to polymer.

Mechanisms are relevant for manufacturing polymeric separation membranes.

Abstract

When a polymer solution undergoes viscoelastic phase separation, the polymer-rich phase forms a network-like structure even if it is a minor phase. This unique feature is induced by polymer dynamics, which are constrained by the temporal entanglement of polymer chains. The fundamental mechanisms of viscoelastic phase separation have already been elucidated by theory and experiments over the past few decades; however, it is not yet well understood how viscoelastic phase separation occurs in multicomponent polymer solutions. Here, we construct a new viscoelastic phase separation model for ternary polymer solutions that consist of a polymer, solvent, and nonsolvent. Our simulation results reveal that a network-like structure is formed in the ternary bulk system through a phase separation mechanism similar to that observed in binary polymer solutions. A difference in dynamics is also found in that the solvent, whose affinity to the polymer is similar to that to the nonsolvent, moves freely between the polymer-rich and water-rich phases during phase separation. These findings are considered important for understanding the phase separation mechanism of ternary mixtures often used in the manufacturing of polymeric separation membranes.