Abstract
Twist-spun carbon nanotube (CNT) yarns exhibit a large and reversible rotational behavior under specific boundary conditions. In situ polarized Raman spectroscopy revealed that a tension-induced twist provides reversibility to this rotation. The orientation changes of individual CNTs were followed when twist-spun CNT yarns were untwisted and subsequently retwisted. Twist-spun CNT yarn, when untwisted and subsequently retwisted under the one-ended tethered boundary condition, showed irreversible orientation changes of the individual CNTs due to snarls formed during the untwisting operation, which resulted in macroscopic irreversible rotational behavior of the CNT yarns. In contrast, the orientation changes of the individual CNTs in twist-spun CNT yarn, when operated under the two-ended tethered boundary condition, were hysteretically reversible due to a tension-induced twist, which has not been reported previously. Indeed, the tension-induced twist was observed by following the orientation change of individual CNTs in elongated CNT yarns, which simulated the deformational behavior of the CNT yarn rotated under the two-ended tethered boundary condition.
Highlights
Twist-spun carbon nanotube (CNT) yarns have been suggested as an efficient route to transport the outstanding electrical, thermal, and mechanical properties of CNTs at the nanoscale to the micro/macro scales[1]
Polarized Raman spectroscopy has been used to characterize the orientation of CNTs because the intensity of the G band depends on the orientation of the CNT, i.e., as the orientation angle of the nanotube axis increases with respect to the polarizer direction, the intensity decreases monotonously[19,20]
What initiates such reversible or irreversible rotational behavior of CNT yarn? We investigated this obtaining in situ Raman spectra during torsional testing of CNT yarns as follows
Summary
Twist-spun carbon nanotube (CNT) yarns have been suggested as an efficient route to transport the outstanding electrical, thermal, and mechanical properties of CNTs at the nanoscale to the micro/macro scales[1]. Few analytical studies have been carried out to investigate the orientation change of individual CNTs within a CNT yarn or its effect on the actuation properties, even though the orientation of CNTs is the most important factor in determining the actuation behavior of CNT yarns[16]. Actuation mechanism of a CNT yarn, including large and reversible rotation, has not been explained well because only the change in the orientation angle of CNTs on the surface of the yarns was examined[11,17,18]. Few studies were carried out to quantitatively characterize the average orientation change of individual CNTs while CNT yarns are actuated. The average orientation of individual CNTs were quantitatively determined, from which the actuation mechanism of twist-spun CNT yarns was revealed
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