The weakly negative permittivity with low-frequency-dispersion behavior in percolative carbon nanotubes/epoxy nanocomposites at radio-frequency range

As one of the basic component materials of metamaterials, natural negative dielectric constant (permittivity) materials have attracted more and more attentions; however, the frequency-dispersion mechanism of negative permittivity, especially the preferable low-frequency-dispersion behavior, still needs to be further explored. In this work, we fabricated the carbon nanotubes (CNTs)/epoxy composites by mechanical mixing and pressure forming. By gradually controlling the CNT content, a percolation phenomenon occurred and the conductive mechanism was changed from hopping conductivity to metal-like conductivity. The Debye model was used to describe the dielectric relaxation when the CNT content was below the percolation threshold; the negative permittivity comes from the plasma oscillation of free electrons in CNT networks when the CNT content is exceeding the percolation threshold explained by Drude model; the equivalent circuit analysis was used to analyze a capacitive-inductive transition. Most importantly, a low-frequency-dispersion and weakly negative permittivity occurred in the composites when the CNT content was slightly higher than the percolation threshold, a new Debye-Drude model was put forward to explain the novel frequency dispersion phenomenon of negative permittivity. Our work provides a new method to explain the phenomenon of low-frequency dispersion and will facilitate applications of negative permittivity materials.

Automated summary

This study investigates the frequency dispersion mechanism of negative permittivity in carbon nanotubes (CNTs)/epoxy composites. The Debye model is used to describe the dielectric relaxation when the CNT content is below the percolation threshold, while the Drude model explains the negative permittivity resulting from the plasma oscillation of free electrons in CNT networks above the percolation threshold. A novel Debye-Drude model is proposed to explain the low-frequency dispersion and weakly negative permittivity observed when the CNT content is slightly higher than the percolation threshold.