Physical aging and structural relaxation in polymer nanocomposites

Molecular dynamics simulations of a coarse‐grained polymer nanocomposite model are used to study the impact of nanoparticles on physical aging. The physical aging rate of the composites is obtained from measurements of the per‐particle pair energy, while the (segmental) mean‐squared displacement and creep compliance are used to probe simultaneously the dependence of structural relaxation times on waiting time elapsed since the glass was formed. Although bulk regions behave similarly to a neat polymer glass, interfacial regions exhibit a reduction in the physical aging rate for attractive polymer–nanoparticle interactions. Repulsive interactions lead instead to a significant increase. This change in physical aging rate is found to be proportional to the local mobility of the polymer atoms. By contrast, aging exponents obtained from time‐waiting time superposition of mean‐squared displacements or compliance curves are much less affected by the nanoinclusions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1789–1798, 2009