Electrical and dielectric behaviors and their origins in the three-dimensional polyvinyl alcohol/MWCNT composites with low percolation threshold

The electrical conductivity and dielectric behavior of a three-dimensional composite of polyvinyl alcohol (PVA) and multiwalled nanotubes (MWCNTs) were measured and an extremely low percolation threshold was observed. Two established theories were used to investigate the behaviors of the composites near the percolation threshold, and then the results indicated that the intercluster polarization effect is more reasonable to explain the electrical property of our system in the frequency range of measurement. The high value of the dielectric constant of the composites was attributed to interfacial polarization within the bulk sample and DC conductance based on charge injection at electrode-sample interface. Thus an equivalent circuit was established by separating the behavior of the bulk sample from that of the electrode-sample interface. The introduction of the concept of Constant Phase Element into the equivalent circuit model gave a fit in good agreement with the experimental data and implied the influence of a fractal interface on the real capacitance. The interfacial polarization and the relaxation processes were fully studied. As a result, the activation energy associated with those relaxation processes in the composites was thought to be the energy needed for the charges accumulating and bounded on the interfaces between MWCNT and PVA. (C) 2009 Elsevier Ltd. All rights reserved.