A Comparative Study of the Electrical and Electromechanical Responses of Carbon Nanotube/Polypropylene Composites in Alternating and Direct Current

The electrical and electromechanical responses of ~200 mu m thick extruded nanocomposite films comprising of 4 wt.% and 5 wt.% multiwall carbon nanotubes mixed with polypropylene are investigated under an alternating current (AC) and compared to their direct current (DC) response. The AC electrical response to frequency (f) and strain (piezoimpedance) is characterized using two configurations, namely one that promotes resistive dominance (resistive configuration) and the other that promotes the permittivity/capacitive contribution (dielectric configuration). For the resistive configuration, the frequency response indicated a resistive-capacitive (RC) behavior (negative phase angle, theta), with a significant contribution of capacitance for frequencies of 10(4) Hz and above, depending on the nanotube content. The piezoimpedance characterization in the resistive configuration yielded an increasing impedance modulus (|Z|) and an increasing (negative) value of theta as the strain increased. The piezoimpedance sensitivity at f = 10 kHz was ~30% higher than the corresponding DC piezoresistive sensitivity, yielding a sensitivity factor of 9.9 for |Z| and a higher sensitivity factor (~12.7) for theta. The dielectric configuration enhanced the permittivity contribution to impedance, but it was the least sensitive to strain.

Automated summary

The electrical and electromechanical responses of nanocomposite films consisting of carbon nanotubes and polypropylene were studied. The effects of alternating current and direct current on the electrical response were investigated. The results showed that the contribution of capacitance to the electrical response was significant at certain frequencies. The sensitivity of the piezoresistive response was higher for alternating current compared to direct current, and the sensitivity to strain was lower in the dielectric configuration.