Effects of carbon nanotubes aspect ratio on the qualitative and quantitative aspects of frequency response of electrical conductivity and dielectric permittivity in the carbon nanotube/polymer composites

To study the effect of carbon nanotube aspect ratio (AR) on the frequency response of the electrical properties, the alternating current (AC) electrical conductivity and dielectric permittivity of different AR multi-wall carbon nanotubes (MWCNTs)/thermoplastic elastomer (TPE) composites were studied in the AC frequency range of 100 Hz to 10 MHz. Qualitatively, the effect of frequency on the electrical properties of the composites was the same for all AR MWCNTs and shared many typical features of electrically percolative composites. Quantitatively, the frequency responses of electrical properties were found to be independent of nominal AR, concentration, percolation threshold, and the diameter of the MWCNT. Instead, frequency response of electrical properties was dependent on the MWCNT length and initial electrical conductivity of the composites. With the same initial conductivity of the MWNT composites, frequency-conductivity sensitivity varied inversely with the nominal length of the MWCNTs. Composites with MWCNTs of the same nominal length and similar electrical conductivity values, regardless of whether the MWCNT concentration was below or above the percolation threshold, exhibited quantitatively similar frequency-conductivity sensitivity. The frequency-dielectric sensitivity at the percolation threshold was a reflection of frequency-conductivity sensitivity and was also found to be dependent on the initial conductivity of the composites.