A new approach for the interpretation of the dynamic and mechanical properties of polymer nanocomposites above and below the glass transition region

TL;DR

This paper introduces a novel model for analyzing the dynamic and mechanical behavior of polymer nanocomposites across the glass transition, linking thermodynamic heterogeneities to their mechanical reinforcement.

Contribution

The work presents a new temperature-dependent model incorporating a characteristic glass transition temperature and structural heterogeneities for polymer nanocomposites.

Findings

The model accurately describes the temperature and pressure dependence of density.

Mechanical reinforcement correlates with the extent of the glassy region.

The approach links dynamical heterogeneities to structural features.

Abstract

In this work, we present a new model for the interpretation of the local dynamic behavior and the mechanical reinforcement mechanism in polymer nanocomposites. The temperature dependence of the dynamics in the glassy region is described by a new equation which assumes an Arrhenius component in the cooperative diffusion. By doing so, a characteristic temperature which can be identified as the glass transition temperature (Tg) emerges, while an additional parameter for the extension of the super-Arrhenius region is incorporated. Based on thermodynamic arguments, the dynamical heterogeneities are then related to structural heterogeneities in a manner consistent with the idea of a sigmoidal shape in the cohesion energy. Incorporation of this temperature dependence of the cohesion energy to a Sanchez-Lacombe Equation of State, results in a sound description of the experimental temperature and pressure dependence of the density. Moreover, comparison with experimental data shows that the enhancement of mechanical properties in polymer nanocomposites can be associated with the extent of the glassy region.