Resolving Segmental Polymer Dynamics in Nanocomposites\nby Incoherent Neutron Spin–Echo Spectroscopy

Abstract

The\nsegmental dynamics of styrene–butadiene nanocomposites with\nembedded silica nanoparticles (NPs, ca. 20 vol. %) has been studied\nby broadband dielectric (BDS) and neutron spin–echo spectroscopy\n(NSE). It is shown by BDS that overlapping contributions only allow\nus to conclude on a range of distributions of relaxation times in\nsimplified industrial nanocomposites formed with highly polydisperse\nNPs. For comparison, structurally similar but less aggregated colloidal\nnanocomposites have a well-defined distribution of relaxation times\ndue to the reduced influence of interfacial polarization processes.\nThis distribution is widened with respect to the neat polymer, without\nchange in the position of the maximum and at most a small slowing\ndown visible in the average time. We then demonstrate that incoherent\nNSE can be used to resolve small modifications of segmental dynamics\nof the industrial samples. By carefully choosing the q-vector of the\nmeasurement, experiments with fully hydrogenated polymer give access\nto the self-dynamics of the polymer in the presence of silica on the\nscale of approximately 1 nm. Our high-resolution measurements show\nthat the segmental motion is slightly but systematically slowed also\nby the presence of the industrial filler NPs.