Complex permittivity of polymer-based composites with carbon nanotubes in microwave band

Abstract

Epoxy composites filled with multiwall carbon nanotubes (MWCNTs) were prepared. Frequency dependencies (in the range 1–67 GHz) of complex dielectric permittivity of the composites were experimentally obtained and the effects of filler (0–0.023 vol. fr.) content on the dielectric properties of composites were investigated. Calculations of the concentration dependence of the dielectric permittivity under the Maxwell-Garnett model were carried out. The analysis showed that the calculations within the Maxwell-Garnett model, which take into account the dielectric characteristics of the components of composite and the aspect ratio of the nanotubes used as filler give coincidence with the experimental data only in the region φ < 0.006 vol. fr. The permittivity of composites was calculated within a power-law relation which considers an aspect ratio of the filler’s particles, value of an interface thickness and its dielectric characteristics. For the thickness of the interface of 40 nm in the investigated MWCNTs/epoxy composites, its permittivity was found to be 21.22 − i × 4.45. Considerations about fitting parameters and the most appropriate model to describe the concentration dependence of dielectric permittivity are given.