Electrical permittivity and conductivity of carbon black-polyvinyl chloride composites

Electrical conductivity and permittivity of carbon black-polyvinyl chloride composites were studied over a wide frequency spectrum (dc, 1.3 GHz). Conductivity of the bulk composites increases with higher volume fraction of carbon black as expected. However, the functional dependence of the increasing conductivity with carbon black loading is different below and above the percolation threshold because ofthe different mechanisms involved. Bulk electric permittivity increases until the composite percolation is reached and then decreases to zero after fully connected conductive paths have been established. Such highly loaded composites showed a metal-like electrical behavior. Different electrical percolation threshold of the composites were found for different species ofcarbon black. Carbon blacks with the lowest packing efficiency reach the percolation threshold with the least volume fraction ofcarbon black loading. The percolation behavior ofspherical carbon blacks showed good agreement with Bruggeman's effective-medium theory in terms of both the percolation threshold and frequency dependence of conductivity at percolation.