Piezoimpedance of carbon nanotube yarns coupled with Raman spectroscopy and its implementation for sensing polymerization kinetics

The electrical response of carbon nanotube yarns (CNTYs) under alternating (AC) and direct current (DC) is investigated. Electrical measurements are conducted simultaneously with application of strain and under in situ Raman spectroscopy. In situ Raman spectroscopy is used to better understand the loading mechanisms and the electromechanical response of the CNTY upon axial stretching. The AC electrical response of the CNTYs is dominated by its resistive component, and a capacitive contribution arises at high frequencies (f > 105 Hz). This response obeys the hierarchical structure of the CNTY, where porosity between bundles form microcapacitors. Under AC, the impedance modulus showed a positive electrical sensitivity to strain with a maximum value of 0.33 at 100 kHz. This is slightly higher than the DC one (0.25). The AC phase angle showed very low sensitivity to strain. The small shift of the Raman bands with strain suggests that structural deformations at the bundle level are the dominant deformation mechanism. While the Raman shift is weak to identify unwinding and detaching of bundles, both the AC and DC electrical responses pinpoint such damage mechanisms by a change in trend. The promising application of the impedance response to monitor the curing kinetics of thermosetting polymers is proved.