Complex ac conductivity of a carbon black composite as a function of frequency, composition, and temperature

Abstract

The complex conductivities between 10 mHz and 1 MHz of a series of disordered carbon-black-polymer composites have been measured. The carbon black volume fractions span the percolation threshold, with dc conductivities ranging from ${10}^{\ensuremath{-}18}$ to ${10}^{\ensuremath{-}6}(\ensuremath{\Omega}\mathrm{cm}{)}^{\ensuremath{-}1}.$ The room temperature results are similar to previous measurements on other percolation systems. Conductivity measurements as a function of temperature on a composite sample, slightly above the room-temperature percolation threshold, are consistent with the percolation threshold increasing with temperature and becoming equal to the actual volume fraction at about 130 \ifmmode^\circ\else\textdegree\fi{}C. The real conductivity at different temperatures is shown to scale onto a single curve. An anomalous peak in the real dielectric constant as a function of composition close to the percolation threshold is also observed.