Slow Linear Viscoelastic Relaxation of Polymer Nanocomposites: Contribution from Confined Diffusion of Nanoparticles

Abstract

In this work, we investigated the linear rheology of polymer nanocomposites with the purpose to find the correlation with the confined diffusion of nanoparticles (NPs), whose diameter (2Rp) is larger than the entanglement mesh size ae of the polymer matrix. The diffusion of NPs is confined by the entanglements of polymer chains at shorter time scale and the particle cages at longer time scale. Diffusion out of entanglement networks is subdiffusive and relies on the retarded relaxation of sticky polymer chains, while the diffusion out of particle cage is a hopping process. Linear viscoelasticity predicted from the generalized Stokes–Einstein relation using the particle diffusion dynamics can describe the experimental data quantitatively. It is found that the characteristic parameters of confined diffusion out of entanglement networks depend solely on the effective surface area of NP clusters. For the diffusion out of the particle cages, the size of the cage equals to the mean interparticle surface distance...