Synergistic effect of CB and MWCNT on the strain-induced DC and AC electrical properties of PVDF-HFP composites

Abstract In this study, carbon black (CB)/multi-walled carbon nanotube (MWCNT)/polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) composite films were fabricated as strain sensors. The sensing characteristics of the composite films both in the direct current (DC) and alternating current (AC) circuits were systematically tested. It was found that the hybrid nanofiller could effectively improve both the electrical conductivity and the sensitivity of the nanocomposites at a given loading far below the percolation threshold of a single filler. At 3.0% tensile strain, the highest DC and AC gauge factors for the nanocomposites with 1.0 wt.% CB and 0.1 wt.% MWCNT were 10.67 and 10.38, respectively, which were 1992.2% and 75.9% higher than those of the composites filled with 2.0 wt.% CB only. In addition, both the relationship of the strain-resistance change rate in the DC condition and the strain-DLT (the dielectric loss tangent) change rate in the AC condition of the nanocomposites with the hybrid nanofiller showed an approximatively linear characteristic, which demonstrated that the linearity of the nanocomposite sensor could be controlled by properly adjusting the content of CB and MWCNT. Finally, the mechanism of the synergistic effect was investigated by inspecting the microstructure of the nanocomposites and an equivalent RLC circuit model.