AC electrical conductivity in polyethylene/carbon black composites

It is well known that AC electrical conductivity /spl sigma/*(f) has similar behavior in a large variety of disordered materials. Semiconductors, amorphous and glassy solids, organic systems, ceramics and polymers exhibit a plateau in the real conductivity curve, /spl sigma/'(S) vs. f, one at low frequencies and another at higher frequencies values. For intermediate frequency values the conductivity increases obeying the relation /spl sigma/'(f)/spl prop/f/sup n/ (0/spl les/n/spl les/1). In this paper, AC electrical conductivity measurements, at different temperatures, were carried out in films aging and unaging of LDPE charged with different carbon-black concentrations. We intend to give a contribution how the dispersed carbon black molecule contributes in the electrical conduction. Both the real /spl sigma/'(f) and the imaginary /spl sigma/''(f) components of the conductivity are analyzed with the help of the random free energy barrier model to fit the experimental results. This model is based on carrier conduction via hopping mechanism-or phonon assisted tunneling process-among localized sites, whose transition rate depends on the spatial distance and on the energy difference between two involved sites.