Influence of Nanoparticle Additives on the Fragility of Polymer Glass Formation and the Buchenau Relation

We investigate the impact of the addition of nanoparticles (NP) on the fragility of a model glass-forming polymer melt by molecular dynamics simulations. We find significant changes in fragility for nanoparticle volume fractions $\phi$ exceeding $\approx$ 5%, where fragility changes correlate with the inverse variance of the magnitude of the Debye-Waller factor $<u^2>$, a measure of local "stiffness" fluctuations. We also confirm the validity of the Buchenau relationship between $<u^2>$ and the structural relaxation time $\tau$ for all $\phi$ and polymer-NP interaction types.