Nanoparticle motion within glassy polymer melts.

X-ray photon correlation spectroscopy is employed to investigate the motion of dilute suspensions of gold nanoparticles in low-molecular-weight polystyrene melts. At high temperatures, the observed motion is diffusive, with a rate that follows a Vogel-Fulcher temperature dependence. Closer to the glass transition temperature Tg, diffusion is superseded by a hyperdiffusive process that first becomes observable near a crossover temperature Tc approximately 1.1Tg and is identified with heterogeneous strain in the melts. Following rapid cooling to temperatures sufficiently below Tc, but still above Tg, the hyperdiffusive dynamics displays a time dependence similar to aging in polymer glasses.