Crowding of Polymer Coils and Demixing in Nanoparticle-Polymer Mixtures

TL;DR

This paper investigates how nanoparticle crowding influences polymer coil sizes and phase stability in mixtures, using adapted models and simulations to reveal stabilization effects due to polymer compression and penetrability.

Contribution

It introduces an adapted AOV model for penetrable, polydisperse polymers and compares simulation results with free-volume theory to understand crowding effects.

Findings

Nanoparticles compress polymer coils, reducing their size.

Polymer compressibility and penetrability stabilize mixtures.

Simulations agree with free-volume theory predictions.

Abstract

The Asakura-Oosawa-Vrij (AOV) model of colloid-polymer mixtures idealizes nonadsorbing polymers as effective spheres that are fixed in size and impenetrable to hard particles. Real polymer coils, however, are intrinsically polydisperse in size (radius of gyration) and may be penetrated by smaller particles. Crowding by nanoparticles can affect the size distribution of polymer coils, thereby modifying effective depletion interactions and thermodynamic stability. To analyse the influence of crowding on polymer conformations and demixing phase behaviour, we adapt the AOV model to mixtures of nanoparticles and ideal, penetrable polymer coils that can vary in size. We perform Gibbs ensemble Monte Carlo simulations, including trial nanoparticle-polymer overlaps and variations in radius of gyration. Results are compared with predictions of free-volume theory. Simulation and theory consistently predict that ideal polymers are compressed by nanoparticles and that compressibility and penetrability stabilise nanoparticle-polymer mixtures.