Filler-Induced Composition Waves in Phase-Separating Polymer Blends

TL;DR

This study computationally explores how immobile filler particles influence phase separation in polymer blends, revealing early concentration waves and patterns that depend on composition and filler affinity, aligning with experimental observations.

Contribution

It introduces a generalized CHC model to simulate filler effects on phase separation, highlighting the formation of target and encapsulation patterns based on filler properties and blend composition.

Findings

Filler particles induce early concentration waves in near-critical blends.

Target patterns form around fillers but are overtaken by background spinodal patterns.

Encapsulation layers develop instead of target patterns in far-from-critical blends.

Abstract

The influence of immobile filler particles (spheres, fibers, platelets) on polymer blend phase separation is investigated computationally using a generalization of the Cahn-Hilliard-Cook (CHC) model. Simulation shows that the selective affinity of one of the polymers for the filler surface leads to the development of concentration waves about the filler particles at an early stage of phase separation in near critical composition blends. These "target" patterns are overtaken in late stage phase separation by a growing "background" spinodal pattern characteristic of blends without filler particles. The linearized CHC model is used to estimate the number of composition oscillations emanating from isolated filler particles. In far-off-critical composition blends, an "encapsulation layer" grows at the surface of the filler rather than a target pattern. The results of these simulations compare favorably with experiments on filled phase separating blend films.