Significantly improved dielectric properties of multiwall carbon nanotube-BaTiO3/PVDF polymer composites by tuning the particle size of the ceramic filler

Abstract

The effects of different BaTiO₃ 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 10³ 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 >10³, respectively. Greatly enhanced dielectric properties are described in detail.