  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.

Soft Condensed Matter;Materials Science