Glass transition and molecular dynamics in poly(dimethylsiloxane)/silica nanocomposites

The molecular dynamics of a series of poly(dimethylsiloxane) networks filled with silica nanoparticles synthesized in situ was investigated using thermally stimulated depolarization currents, broadband dielectric relaxation spectroscopy and differential scanning calorimetry. The techniques used cover together a broad frequency range (10−3–109 Hz), thus allowing to gain a more complete understanding of the effects of the nanoparticles on the chain dynamics. In addition to the α relaxation associated with the glass transition of the polymer matrix, we observe in dielectric measurements a slower α relaxation which is assigned to polymer chains close to the polymer/filler interface whose mobility is restricted due to interactions with the filler surface. The thickness of the interfacial layer is estimated to be about 2.1–2.4 nm. Differential scanning calorimetry shows a change in the shape of the glass transition step, as well as a decrease in both the degree of crystallinity and the crystallization rate by the addition of silica.