  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.
