Microphase separation in neutral homopolymer blends induced by salt-doping

TL;DR

This paper demonstrates that neutral homopolymer blends can undergo microphase separation upon salt-doping due to ion solvation effects, offering a new low-cost method for nanostructure fabrication.

Contribution

It introduces a minimal model showing microphase separation in neutral homopolymers with salt, driven by ion solvation and dielectric contrast, which was previously thought unlikely.

Findings

Microphase separation occurs in neutral homopolymer blends with salt.

Ion solvation and dielectric contrast drive the separation.

Factors like ion size and polymer fraction influence the behavior.

Abstract

Microphase separation in polymeric systems provides a bottom-up strategy to fabricate nanostructures. Polymers that are reported to undergo microphase separation usually include block copolymers or polyelectrolytes. Neutral homopolymers, which are comparatively easy to synthesize, are thought to be incapable of microphase separation. Here, using a minimal model that accounts for ion solvation, we show that microphase separation is possible in neutral homopolymer blends with sufficient dielectric contrast, upon a tiny amount of salt-doping. The driving force for the microphase separation is the competition between selective ion solvation, which places smaller ions in domains with higher dielectric constant, and the propensity for local charge neutrality to decrease the electrostatic energy. The compromise is an emergent length over which microphase separation occurs and ions are selectively solvated. The factors affecting such competitions are explored, including ion solvation radii, dielectric contrast, and polymer fraction, which point to directions for observing this behavior experimentally. These findings suggest a low-cost and facile alternative to produce microphase separation which may be exploited in advanced material design and preparation.