The Impact of an Emergent Hierarchical Filler Network on Nanocomposite Dynamics*

The performance of nanoscale-filled elastomers is related to the structure of the aggregated filler network in addition to interfacial chemical affinity and filler dispersion. This structure emerges due to a competition between the thermodynamically driven filler immiscibility and the kinetically driven mixing process. A hierarchical filler network model evidenced in x-ray scattering is linked to the dynamic response at low strains in the linear viscoelastic regime. The primary nanoscale network that percolates locally at ~5 vol % displays a mesh-size, which is related to the changes in the dynamic spectrum at frequencies below the Einstein-Smallwood enhancement associated with the elastomer within the network pores in the high frequency region. The secondary micron-scale network associated with the Payne effect and bulk electrical conductivity that percolates globally at ~20 vol %, influences the gel-like dynamic response at very low frequencies. The hierarchical filler network is described by two crossover frequencies in the dynamic spectrum and two related structural scaling regimes.