Electrical properties of dispersions of graphene in mineral oil

Dispersions of graphene in mineral oil have been prepared and electrical conductivity and permittivity have been measured. The direct current (DC) conductivity of the dispersions depends on the surface characteristics of the graphene platelets and followed a percolation model with a percolation threshold ranging from 0.05 to 0.1 wt. %. The difference in DC conductivities can be attributed to different states of aggregation of the graphene platelets and to the inter-particle electron transfer, which is affected by the surface radicals. The frequency-dependent conductivity (sigma(omega)) and permittivity (epsilon(omega)) were also measured. The conductivity of dispersions with particle contents much greater than the percolation threshold remains constant and equal to the DC conductivity at low frequencies omega with and followed a power-law sigma(omega) proportional to omega(s) dependence at very high frequencies with s approximate to 0.9. For dispersions with graphene concentration near the percolation threshold, a third regime was displayed at intermediate frequencies indicative of interfacial polarization consistent with Maxwell-Wagner effect typically observed in mixtures of two (or more) phases with very distinct electrical and dielectric properties. (C) 2014 AIP Publishing LLC.