Broadband dielectric characterization of carbon black-reinforced natural rubber

Natural rubber compounds reinforced with two different carbon blacks (N134 and N330) at various concentrations were characterized using very broadband dielectric spectroscopy from around 0.1 Hz to 0.3 THz using four different impedance and network analysis technologies. Percolation behavior was observed when the testing electrical frequency was below a certain range, which can be linked to the presence of percolated carbon black networks. When above a critical frequency level, the real part of AC conductivity or the permittivity tended to have a simple exponential relationship with the volume fraction of carbon black rather than a percolation-like behavior with the carbon black volume fraction and was no longer sensitive to carbon black networks. The AC conductivity derived via complex impedance was also strongly influenced by the choice of calculation model when the material was around or below the percolation threshold.