Dispersion, Glass Transition and Dynamics in Nanocomposites with Non-linear Polymers

We prepared nanocomposites of spherical nanoparticles and polymer matrices with various architectures (from linear to stars and hyper-branched) to understand the effect of polymer topology on the composite microstructure, thermal and rheological behavior. Two different sizes of nanoparticles and wide range of concentrations from a few percent up to fifty percent (by volume) were systematically investigated using DSC, rheology, static and dynamic light scattering, x-ray scattering, and neutron scattering. The results show that chain compactness is the key factor for determining the glass transition and the rheological behavior of these nonlinear polymer nanocomposites. Compact polymers induce less reinforcement compared to the loose linear chains due to less penetrability and weaker inter-chain entanglements of compact architectures. In all cases, the differences in mechanical reinforcement are amplified in the confined regime where the dynamics is controlled primarily by the surface bound polymers. These results are corroborated with the polymer segmental dynamics measured using quasielastic neutron backscattering.