The effects of agglomerate on the piezoresistivity of conductive carbon nanotube/polyvinylidene fluoride composites

Conductive polymer composites are prepared with a polyvinylidene fluoride (PVDF) matrix and multiwalled carbon nanotube (MWCNT) as filler. The mechanical properties, electrical conductivity and piezoresistivity of the composites are investigated as a function of MWCNT volume fraction. An optimal combination of ductility and piezoresistivity is found in the composite slightly above the electrical percolation threshold, showing a maximum fracture strain ∼ 4 times higher than the pure PVDF samples, as well as an outstanding sensitivity of piezoresistive response. Increasing further the MWCNT volume fraction leads to deterioration of both ductility and piezoresistivity. The effects of MWCNT content on piezoresistivity and fracture strain can be understood based on the microstructure observations. In particular, by incorporating two characteristic microstructural features identified in the materials, i.e., the filler random distribution and the filler agglomerate, into a simple statistical network model, the experimental measurements of piezoresistivity can be successfully fitted and understood in a semi-quantitative manner.