Electrical properties of epoxy composites with carbon nanotubes, mixed with TiO2 or Fe particles

The electrical properties of ternary epoxy composite materials (CMs) with carbon nanotubes (CNT) and additional inorganic fillers such as carbonyl iron (Fe) and titanium dioxide (TiO2) particles have been investigated The study of electrical conductivity at direct current (DC) showed the increase of percolation threshold in ternary composites compared with two-phase CNT/epoxy CMs. On the other hand, sufficient enhancement of DC conductivity was observed for ternary CNT-based CMs at CNT content higher than 4 wt%. The impedance spectroscopy study at frequency range 10 Hz–2 MHz revealed the increase of conductivity with frequency for most CMs and each CM has a frequency, below which the conductivity stays constant. The equivalent circuit model has been used to model the complex impedances of the CMs and good matching of modeled and measured impedance diagrams was achieved, allowing it to determine the equivalent electrical parameters of the CMs. The impedance spectra show a transition from pure dielectrics at 0 wt% CNT to conductive material for 3–5 wt% CNT in three-phase epoxy composites. The sufficient higher values of permittivity were found for three-phase epoxy composites compared with two-phase CNT/epoxy CMs. The observed negative value of permittivity for 5%CNT/Fe/epoxy CM at higher frequencies is related to metal-like behavior of composite and described within the Drude model. The developed multi-phase epoxy composites may be promising for applications in electronics such as capacitors and electric field grading materials, electromagnetic interference shielding and microwave absorptive materials.