Improve the dielectric property and breakdown strength of composites by cladding a polymer/BaTiO3 composite layer around carbon nanotubes

This work offers a strategy for combining ceramic and conductive fillers to produce composites with high dielectric properties and breakdown strength through a novel core@shell structure. First, we successfully attached barium titanate (BT) nanoparticles to the surface of multi-walled carbon nanotubes (MWCNTs) by sol-gel method. Hyperbranched aromatic polyamide (HB-Pa) was grafted from the surface of BT-attached MWCNTs via in suit polymerization to obtain HB-Pa/BT composite-coated MWCNTs (H-B@CNTs). After the hybrid powders were compounded with epoxy resin (EP), composites with high dielectric properties were prepared. The H-B@CNTs/EP composite exhibited a dielectric constant of 110, a dielectric loss of 0.28 (1 kHz) and a breakdown strength of 6.7 kV/mm at 20 wt % MWCNTs content. The results indicated that we could tailor the dielectric properties of composites by adjusting the amount of BT nanoparticles on the surface of MWCNTs. In addition, HB-Pa played multiple roles in this system: (i) preventing BT nanoparticles from falling off the surface of MWCNTs; (ii) increasing the dispersibility and interaction of fillers in the polymer matrix ; (iii) preventing MWCNTs from overlapping one another to form a conductive network to effectively improve the breakdown strength of composites.