Dynamics in polymer and polymer-grafted nanocomposites: it's the interfacial zone after all

Polymers exhibit deviations from their bulk physical properties in the vicinity of solid substrates due to changes in various properties arising in the interfacial regions. Broadband dielectric spectroscopy and differential scanning calorimetry are used to study molecular dynamics in poly(methyl methacrylate)/silica nanoparticle composites. By systematically examining nanocomposites based on non-functionalized Si NPs dispersed in PMMA matrices and on PMMA-grafted Si NPs in PMMA matrices, we investigate the effects of interfacial interactions and confinement in each of these cases on Tg and the time-scales as well as breadth of the corresponding dielectric relaxations. We show that in addition to slower mobility, which is commonly reported in literature and assigned to interfacial relaxations, faster modes also arise due to confinement effects, and that these faster modes are more pronounced in nanocomposites with polymer-grafted nanoparticles. These faster relaxation modes are attributed to the increasing importance of chain wetting and packing in the interfacial zones around nanofillers.