Dielectric Characterization of Core-Shell Structured Poly(vinylidene fluoride)-grafted-BaTiO3 Nanocomposites

Dielectric properties of poly(vinylidene fluoride)-grafted-BaTiO3 (PVDF-g-BT) core-shell structured nanocomposites obtained from Reversible Addition Fragmentation chain Transfer (RAFT) polymerization of VDF were investigated by Broadband Dielectric Spectroscopy (BDS). The dielectric constant increased along with the BT content, about +50% by addition of 15 vol% of BT, which was around 40% more than expected from predictions using the usual dielectric modeling methods for composite materials, to be ascribed to the effect of the interfacial core-shell structure. The known dielectric relaxations for PVDF were observed for the neat polymer as well as for its nanocomposites, not affected by the presence of nanoparticles. A relaxation process at higher temperatures was found, due to interfacial polarization at the amorphous-crystalline interface, due to the high crystallinity of materials produced by RAFT. Isochronal BDS spectra were exploited to detect the primary relaxation of the amorphous fraction. Thermal analysis demonstrated a very broad endotherm at temperatures much lower than the usual melting peaks, possibly due to the ungrafted fraction of the polymer that is more easily removable by repeated washing of the pristine material with acetone.

Automated summary

The dielectric properties of PVDF-g-BT core-shell structured nanocomposites obtained by RAFT polymerization were investigated. The dielectric constant increased with the addition of BT, exhibiting a larger increase than predicted by usual modeling methods for composite materials, due to the effect of the interfacial core-shell structure. PVDF's known dielectric relaxations were observed in both the neat polymer and its nanocomposites, unaffected by the presence of nanoparticles. A relaxation process due to interfacial polarization was found at higher temperatures, attributed to the high crystallinity of the materials produced by RAFT.