Origin of remarkable positive temperature coefficient effect in the modified carbon black and carbon fiber cofillled polymer composites

In order to achieve a desired conductivity and further improvement in positive temperature coefficient (PTC) effect, carbon fibers (CFs) are incorporated into the modified nanoscale carbon black (MNCB) filled polymer composites. The CF with high aspect ratio can easily span across insulating regions and further connect the existing conductive pathways. In this work, the total volume fraction of MNCB and CF is set as 8vol%. When the concentration of CF reaches a certain value, we observe remarkably improved PTC intensity (PTCI). The PTCI is nearly two orders of magnitude larger than that in the MNCB filled polymer (same at 8 vol % loading). When compared to the polymer composites only loaded with MNCB, the negative temperature coefficient effect in the (CF-MNCB)/polymer composites was also weakened to some extent. These results can be explained by considering the change in microstructure of the (CF-MNCB)/polymer composites. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3182818]