Chemically functionalized multi-walled CNTs induced phase behaviors of poly(vinylidene fluoride) nanocomposites and its dielectric properties

Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were selected as the carrier and polypyrrole (PPy) as functional agent to synthesize PPy/MWCNTs dielectric nanofillers via FeCl3 oxidative polymerization of pyrrole (Py) on the surface of MWCNTs-COOHs, and then poly(vinylidene fluoride) based dielectric nanocomposites (PPy/MWCNTs/PVDF) were fabricated by direct melting blending. The effects of the PPy/MWCNTs dielectric nanofillers on the changes of phase behaviors and the mechanical, thermal and dielectric properties of the PPy/MWCNTs/PVDF dielectric nanocomposites were investigated. The results indicated that PPy/MWCNTs/PVDF dielectric nanocomposites showed higher mechanical strength within a certain range of PPy/MWCNTs nanofillers content. When the PPy/MWCNTs content was 10 wt.%, the tensile strength and elastic modulus of the nanocomposites reached 60.2 MPa and 610 MPa respectively, which increased by 24 % and 75 %, in contrast to those of MWCNT-COOH/PVDF dielectric nanocomposites. Dielectric properties tests revealed that the introduction of PPy induced the formation conductive networks and beta-type PVDF, and thus enhancing the dielectric constant. the resultant PPy/MWCNTs/PVDF dielectric nanocomposites reached the percolation threshold at the PPy/MWCNTs content of 12 wt.%. The corresponding dielectric constant reached 83, which was 10 times of pure PVDF. Meanwhile, the dielectric constant was also much higher than MWCNTs-COOH/PVDF. Differential scanning calorimeter (DSC) found that the melting and crystallization temperatures of the two nanocomposites were greatly improved compared with pure PVDF, indicating that the addition of dielectric nanofiller improved the thermal property of the nanocomposites.