Glass Transition and Molecular Dynamics in Core–Shell-Type Nanocomposites Based on Fumed Silica and Polysiloxanes: Comparison between Poly(dimethylsiloxane) and Poly(ethylhydrosiloxane)

Abstract

The interfacial polymer in nanocomposites (PNCs) is widely believed to exhibit modified dynamics and structure, which are considered responsible for the improved PNC properties. Owing to its high resolving power, broadband dielectric spectroscopy (BDS) is one among the most suitable tools for studying polymer dynamics. Here, BDS combined with differential scanning calorimetry (DSC), microscopy, infrared spectroscopy, and thermally stimulated depolarization currents (TSDC) are employed to study low-molecular weight polydimethylsiloxane (PDMS) and a slightly modified siloxane, polyethylhydrosiloxane (PEHS), in bulk and in the form of silica–polymer “core–shell”-type PNCs. The dielectric/calorimetric mapping for the systems based on PEHS is demonstrated for the first time. Bulk-like dynamics (α relaxation, glass transition) is recorded faster and less cooperative in the PNCs, in agreement between the techniques, most probably due to spatial confinement between the neighboring nanoparticles. The constraints a...