Interplay between self-assembly and phase separation in a polymer-complex model

TL;DR

This paper introduces a theoretical model that predicts complex phase behaviors in polymer solutions where self-assembly into complexes influences phase separation, revealing phenomena like re-entrance and distinct phase diagram features.

Contribution

The study combines statistical associating fluid theory with a two-state self-assembly model to explore phase behavior in polymer solutions, highlighting the interplay between assembly and phase separation.

Findings

Re-entrant phase behavior observed in the model.

Graphical derivation of system-specific phase diagrams.

Phase diagrams can resemble but differ from lower critical solution temperature systems.

Abstract

We present a theoretical model for predicting the phase behavior of polymer solutions in which phase separation competes with oligomerization. Specifically, we consider scenarios in which the assembly of polymer chains into stoichiometric complexes prevents the chains from phase-separating via attractive polymer-polymer interactions. Combining statistical associating fluid theory with a two-state description of self-assembly, we find that this model exhibits rich phase behavior, including re-entrance, and we show how system-specific phase diagrams can be derived graphically. Importantly, we discuss why these phase diagrams can resemble -- and yet are qualitatively distinct from -- phase diagrams of polymer solutions with lower critical solution temperatures.