Two-Population Rouse Models for Polymer Segmental Dynamics in Nanocomposites

Polymer Nanocomposites (PNC) can enhance the mechanical properties over the host polymer. Greater understanding of their microstructure and dynamics is needed to effectively design PNC with improved characteristics. Using quasi-elastic neutron scattering, we probed the polymer segmental dynamics in well dispersed attractive PNC comprised of poly(ethylene oxide) and elongated silica Nanoparticles (NP), identifying two populations of segments with different mobility: bulk-like and a slow interfacial layer. While the Rouse model is appropriate for the bulk-like fraction, its modification is required to accurately describe the dynamics of the interfacial layer. Two hypotheses for interfacial dynamics are investigated. The first treats the interfacial layer as having a Rouse parameter from the bulk, attributed to a higher density of interfacial layer. The second considers suppression of the Rouse modes (beyond what is expected in the neat polymer from entanglement) due to the increased topological constraint on adsorbed chains. Quantitative information on the slowing down of the dynamics at the interface, as well as its spatial extent are obtained. These results are relevant for the understanding of the mechanism of reinforcement in polymer nanocomposites.