Electrical characterization of carbon-based fibers and their application for sensing relaxation-induced piezoresistivity in polymer composites

Abstract

The direct current (DC) and alternating current (AC) electrical responses of carbon fibers (CFs), carbon nanotube yarns (CNTYs) and glass fibers containing carbon nanotubes (CNTs) on their surface (GF-CNT) are investigated. Under DC, CFs and CNTYs exhibit a nearly Ohmic global response for up to ∼12 μA, although important local variations in the linearity of the current-voltage curves are observed for CNTYs. GF-CNTs, on the other hand, yield a non-Ohmic response. Consistently, under AC, CFs and CNTYs present only a small increase in impedance at high frequencies (∼2 MHz) with larger variations in the phase angle for CNTYs. The discontinuous architecture of the CNT conductive network of GF-CNT yields a rapid and significant decrease of impedance modulus and phase angle as the frequency increases, evidencing microcapacitance effects. Polymeric monofilament composites were manufactured with these three types of fibers, and the piezoresistive behavior induced by viscoelastic relaxation was evaluated. All monofilament composites presented changes in their electrical resistance in response to polymer viscoelastic relaxation, and the sign and magnitude of the electrical resistance change showed a strong dependence on the fiber architecture.