Decoupling nanoparticle motion from elastic modulus in polymer nanocomposites in confined regime

We investigated slow motion of nanoparticles individually dispersed in entangled polymer melts at particle volume fractions up to 42 %. At such high loadings, the nanoparticles serve as both fillers for the resulting polymer nanocomposites and probes for the network dynamics therein. The results from x-ray photon correlation spectroscopy revealed that the particle relaxation closely follows the mechanical reinforcement in the nanocomposites only at the intermediate concentrations below the critical value for the chain confinement. Interestingly, the particles do not further slowdown at higher volume fractions- when all chains are practically on nanoparticle interface- and their motion decouple from the elastic modulus of the nanocomposites that further increases orders of magnitude.