Interfacial Entropic Interactions Tunes Fragility and Dynamic Heterogeneity of Glassy Athermal Polymer Nanocomposite films

TL;DR

This study explores how interfacial entropic interactions in polymer nanocomposites influence their fragility and dynamic heterogeneity, revealing that increased entropic compatibility enhances fragility but exhibits an unexpected anti-correlation with dynamical heterogeneity.

Contribution

It demonstrates how altering interfacial layer dynamics through grafted polymer size ratio affects fragility and heterogeneity in athermal glassy polymer nanocomposites, revealing novel anti-correlated behaviors.

Findings

Fragility increases with interfacial entropic compatibility.

An anti-correlation exists between fragility and dynamical heterogeneity.

Interfacial layer dynamics significantly influence glassy polymer nanocomposite properties.

Abstract

Enthalpic interactions at the interface between nanoparticles and matrix polymers is known to influence various properties of the resultant polymer nanocomposites (PNC). For athermal PNCs, consisting of grafted nanoparticles embedded in chemically identical polymers, the role and extent of the interface layer (IL) interactions in determining the properties of the nanocomposites is not very clear. Here, we demonstrate the influence of the interfacial layer dynamics on the fragility and dynamical heterogeneity (DH) of athermal and glassy PNCs. The IL properties are altered by changing the grafted to matrix polymer size ratio, f, which in turn changes the extent of matrix chain penetration into the grafted layer. The fragility of PNCs is found to increase monotonically with increasing entropic compatibility, characterized by increasing penetration depth. Contrary to observations in most polymers and glass formers, we observe an anti-correlation between the dependence on IL dynamics of fragility and DH, quantified by the experimentally estimated Kohlrausch-Watts-Williams parameter and the non-Gaussian parameter obtained from simulations.