Structure and dynamics of a polymer-nanoparticle composite: Effect of nanoparticle size and volume fraction

TL;DR

This study uses molecular dynamics simulations to explore how nanoparticle size and concentration affect the structure, dynamics, and polymer chain behavior in a polymer-nanoparticle composite, revealing size-dependent swelling and contraction effects.

Contribution

It provides new insights into how nanoparticle size and volume fraction influence polymer chain conformation and particle diffusion in composite materials.

Findings

Polymer chains swell with larger nanoparticles and contract with smaller ones.

Diffusion coefficients decrease with increasing nanoparticle volume fraction.

Beyond a certain volume fraction, nanoparticles aggregate, altering diffusion behavior.

Abstract

We use molecular dynamics simulations to study a semidilute, unentangled polymer solution containing well dispersed, weakly attractive nanoparticles (NP) of size ($\sigma_N$) smaller than the polymer radius of gyration $R_g$. We find that if $\sigma_N$ is larger than the monomer size the polymers swell, while smaller NPs cause chain contraction. The diffusion coefficient of polymer chains ($D_p$) and NPs ($D_N$) decreases if the volume fraction $\phi_N$ is increased. The decrease of $D_p$ can be well described in terms of a confinement parameter, while $D_N$ shows a more complex dependence on $\sigma_N$, which results from an interplay between energetic and entropic effects. When $\phi_N$ exceeds a $\sigma_N$-dependent value, the NPs are no longer well dispersed and $D_N$ and $D_p$ increase if $\phi_N$ is increased.