Significantly improved dielectric properties of multiwall carbon nanotube-BaTiO 3 /PVDF polymer composites by tuning the particle size of the ceramic filler.

The effects of different BaTiO 3 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 ( f CNT ) are systematically characterized. The dielectric permittivity ( ε ') of the CNT-nBT/PVDF and CNT-μBT/PVDF composites rapidly increases when f CNT > 0.015 and f CNT > 0.017, respectively. The former is accompanied by the dramatic increase in the loss tangent (tan  δ ) and conductivity ( σ ), but surprisingly, not for the latter. At 10 3 Hz, the low tan  δ and σ values of the CNT-μBT/PVDF composite are about 0.06 and 6.82 × 10 -9 S cm -1 , while its ε ' value is greatly enhanced (≈154.6). The variation of the dielectric permittivity with f CNT for both composite systems follows the percolation model with percolation thresholds of f c = 0.018 and f c = 0.02, respectively. With further increasing f CNT to 0.02, ε ' is greatly increased to 253.8, while tan  δ ≤ 0.1. Without μBT particles, the ε ' and tan  δ values of the CNT/PVDF composite with f CNT = 0.02 are as high as ≈240 and >10 3 , respectively. Greatly enhanced dielectric properties are described in detail.