Effects of silica and titania nanoparticles of a wide range of size (8 – 80 nm in diameter for primary particles) and specific surface roughness (specific surface area, SBET, 25 – 342 m2/g) on interfacial dynamics of linear polydimethylsiloxane (PDMS) in nanocomposites (NCs) of the core–shell type were studied by employing differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC), and broadband dielectric relaxation spectroscopy (DRS). All techniques revealed an increase of the interfacial polymer fraction with increasing surface roughness and provided some evidence of increased density in the interfacial layer. These effects were accompanied by enhanced dynamics and cooperativity of the corresponding interfacial segmental relaxation (αint relaxation). Results were critically compared with those of conventional NCs based on crosslinked PDMS filled with in situ generated small silica (~5 nm) and titania (~30 nm) nanoparticles. In both core-shell and conventional PDMS based NCs the segmental α relaxation was analyzed in terms of three contributions. In NCS based on a thermoplastic polymer (poly(L–lactic acid), PLLA) filled with nano–inclusions of various sizes and different dimensionality, on the contrary, only a single segmental α relaxation was observed and the dielectric strength was found to systematically decrease in the NCs in correlation to a decrease of the heat capacity change at glass transition.