Broadband electrical conductivity of metal/carbon nanotubes polyamide 6 composites fabricated by reactive encapsulation

This is the first broadband dielectric spectroscopy study on the temperature- and frequency-dependent electrical conductivity of polyamide 6 (PA6) composites containing both metal microparticles (Al, Fe, or Cu) and carbon nanotubes (CNT). The dually reinforced PA6 hybrids are prepared through compression molding of metal- and CNT-loaded microparticles (MP). These MP are synthesized by activated anionic ring-opening polymerization (AAROP) of ε-caprolactam in suspension, carried out in the presence of the micron-sized metal powders and the nanosized CNT fillers, with a combined load of up to 10 wt%. The good dispersion of the two loads by the AAROP strategy results in a notable increase in the electrical conductivity by up to 11 orders of magnitude. Moreover, the frequency-dependent behavior of the measured conductivity obeys the so-called universal dynamic response. This response involves a direct current (d.c.) electrical conductivity ( \({\sigma }_{{\text{dc}}}\) ${\sigma }_{\text{dc}}$ ) observed beyond a critical frequency, \({F}_{{\text{c}}}\) $F_{\text{c}}$ , followed by a power-law response characterized by an exponent s, which fluctuates between 0.11 and 0.43. The \({\sigma }_{{\text{dc}}}\) ${\sigma }_{\text{dc}}$ of the binary composites spans from 1.42 \(\times\) $\times$ 10⁻⁵ to 1.63 \(\times\) $\times$ 10⁻² S/cm, this increase being attributed to the synergetic effect between CNT and the metal particles that contribute to the carrier mobility within the conductive network.