Significantly improved dielectric properties of multiwall carbon nanotube-BaTiO/PVDF polymer composites by tuning the particle size of the ceramic filler.

The effects of different BaTiO sizes (≈100 nm (nBT) and 0.5-1.0 μm (μBT)) on the dielectric and electrical properties of multiwall carbon nanotube (CNT)-BT/poly(vinylidene fluoride) (PVDF) composites are investigated. The fabricated three-phase composites using 20 vol% BT with various CNT volume fractions ( ) are systematically characterized. The dielectric permittivity (') of the CNT-nBT/PVDF and CNT-μBT/PVDF composites rapidly increases when > 0.015 and > 0.017, respectively. The former is accompanied by the dramatic increase in the loss tangent (tan ) and conductivity (), but surprisingly, not for the latter. At 10 Hz, the low tan  and values of the CNT-μBT/PVDF composite are about 0.06 and 6.82 × 10 S cm, while its ' value is greatly enhanced (≈154.6). The variation of the dielectric permittivity with for both composite systems follows the percolation model with percolation thresholds of = 0.018 and = 0.02, respectively. With further increasing to 0.02, ' is greatly increased to 253.8, while tan  ≤ 0.1. Without μBT particles, the ' and tan  values of the CNT/PVDF composite with = 0.02 are as high as ≈240 and >10, respectively. Greatly enhanced dielectric properties are described in detail.