A structure evolution mechanism for the modulus loss in electromechanical response of carbon nanotube fiber

Abstract

Electromechanical response (EMR) of carbon nanotube (CNT) fiber is a collective contraction behavior of CNT network, as a consequence of the densification process of assembly structure under electromagnetic force, Ampère force. Load drop at first electric stimulus in EMR test is the manifestation of modulus loss that is opposite to the densification process. The contradiction between modulus loss and collective contraction behavior provides a novel perspective to investigate the microstructure change in EMR. Herein, a structure evolution mechanism was proposed to explain the modulus loss in EMR. Distance between CNTs in some nodes increased under the Ampère force from adjacent CNTs, and the increasing distance weakened the bond effect of van der Waals force, resulting in the appearance of load drop. A mathematical model was applied to fit the experimental stress-strain curves of CNT fiber with different current intensities, and the variation of relevant parameters supported the structure evolution mechanism. Structure densification process driven by Ampère force was also testified as the working principle of EMR by analyzing the thermal expansion in EMR. The relationship between Ampère force, external load, van der Waals force and modulus loss was also discussed.