Dafne Musino, Julian Oberdisse, Bela Farago, Angel Alegria, and Anne-Caroline Genix
The structure and dynamic properties of nanocomposites made of hard inorganic filler nanoparticles (NPs) dispersed in a polymeric matrix determine many macroscopic properties (mechanical, optical, electrical…) decisive for applications, like e.g. car tire optimization. In the past, we have contributed to the analysis of the microscopic structure of these disordered systems using small-angle X-ray or neutron scattering combined with appropriate modeling approaches. Here, the segmental dynamics of styrene-butadiene nanocomposites made with silica nanoparticles (ca. 20 vol. %) of industrial relevance has been studied by broadband dielectric (BDS) and neutron spin-echo spectroscopy (NSE). It is shown first by BDS that overlapping contributions only allow concluding on a range of distributions of relaxation times in nanocomposites formed with highly polydisperse NPs. We thus investigate the dynamics by NSE and demonstrate – here for the first time – that incoherent NSE based on fully hydrogenated compounds can be used to resolve small modifications of the segmental dynamics of polymer nanocomposites. By carefully choosing the q-vector of the measurement, experiments with fully hydrogenated polymer give access to the self-dynamics of the polymer in the presence of silica on the scale of approximately 1 nm. Our high-resolution measurements show that the segmental motion is slightly but systematically slowed down by the presence of the industrial filler NPs. This slowing down is possibly caused by the confinement of the polymer within dense zones and thus in contact with the NP interface. It is probably correlated with different rheological properties of the polymer close to the NPs, which is turn may affect macroscopic behavior.