Effects of Polymer-Filler Interactions on Controlling the Conductive Network Formation in Polyamide 6/Multi-Walled Carbon Nanotube Composites

This study reports on the effects of polymer-filler interactions, in particular transcrystallization, on controlling the conductive network formation in polyamide 6 (PA6)/multiwalled carbon nanotube (MWCNT) composites. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results show that MWCNTs act as strong heterogeneous nucleating agents for PA6 crystals. Transmission election microscopy (TEM) confirmed the formation of a thick transcrystalline layer on the surfaces of the MWCNTs in PA6/MWCNT composites. Consequently, electrical conductivity measurements revealed that the formation of heterogeneously nucleated PA6 transcrystalline layers on the MWCNTs’ surfaces disrupt direct contact between adjacent MWCNTs and impeded the insulating-to-conductive transition in PA6/MWCNT composites. Thus, the electrical percolation threshold was observed at much higher MWCNT content as compared to the rheological percolation threshold. Interestingly, the current-voltage (I–V) characterizations showed that even at a high MWCNT content of 10 wt%, electron tunneling was the dominant electron conduction mechanism, signifying the lack of direct contact between the adjacent MWCNTs in the PA6/MWCNT composites.