Bulk and Shear Rheology of Silica/Polystyrene Nanocomposite: Reinforcement and Dynamics

Bulk and shear rheological studies were performed on a 10 wt % silica nanoparticle-filled polystyrene nanocomposite. The limiting moduli in glassy and rubbery states are higher for the nanocomposite than for the neat polymer; the increase is consistent with hydrodynamic reinforcement and is slightly higher than the lower bound of the rule of mixtures prediction. All evidence indicates that the presence of nanoparticles does not significantly change the polymer dynamics associated with glass transition, except to increase the T-g by 3 K. Comparison of the bulk and shear retardation spectra suggests that the underlying mechanisms for both responses are similar at short times and that the long-time chain modes available to the shear are not available to the bulk, consistent with Plazek's earlier findings. In addition, T-T-g and TV scaling, along with the findings of thermorheological complexity, are discussed. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 621-632