Dynamics of gold nanoparticles in a polymer melt

Gold nanoparticles are used as a luminescent contrast agent to study size-dependent dynamics in polymer matrix. The experiments measured the diffusion coefficient of particles in poly(butyl methacrylate) melt by tracking their motion within a diffraction-limited focus of a laser with 150 fs pulses at 800 nm. Our results indicate that for unentangled polymers, when the particle radius (R) is greater than the gyration radius (Rg) of the chain, the Stokes–Einstein relation can accurately predict particle dynamics. For longer chains, if the entanglement mesh length is larger than R, the particle diffuses ∼250 times faster than predicted by the Stokes–Einstein relation.