Glassy states and microphase separation in cross-linked homopolymer blends

TL;DR

This paper models the glassy states and microphase separation in cross-linked homopolymer blends using a Landau approach, revealing how gelation influences stability and prevents complete demixing, leading to microphase separation.

Contribution

It introduces a coupled Landau theory to analyze how cross-linking affects phase separation and stability in homopolymer blends, highlighting the role of gelation in microphase formation.

Findings

Gelation enhances blend stability against demixing.

Microphase separation occurs at a finite length scale due to network rigidity.

Complete demixing is prevented by gelation, leading to microphase structures.

Abstract

The physical properties of blends of distinct homopolymers, cross-linked beyond the gelation point, are addressed via a Landau approach involving a pair of coupled order-parameter fields: one describing vulcanisation, the other describing local phase separation. Thermal concentration fluctuations, present at the time of cross-linking, are frozen in by cross-linking, and the structure of the resulting glassy fluctuations is analysed at the Gaussian level in various regimes, determined by the relative values of certain physical length-scales. The enhancement, due to gelation, of the stability of the blend with respect to demixing is also analysed. Beyond the corresponding stability limit, gelation prevents complete demixing, replacing it by microphase separation, which occurs up to a length-scale set by the rigidity of the network, as a simple variational scheme reveals.