Page 290 - Carbon Nanotube Fibres and Yarns

Carbon nanotube yarn-based actuators 279

Fig. 11.7 SEM images of (A) woven fabric actuator made from coiled CNT yarns (scale
bar 500 μm) [46] and (B) CNT/SPX knitted textile (scale bar 100 μm) [47]. (Source of (A): P.
Chen, Y. Xu, S. He, X. Sun, S. Pan, J. Deng, D. Chen, H. Peng, Hierarchically arranged helical fibre
actuators driven by solvents and vapours, Nat. Nanotechnol. 10 (2015) 1077–1084. Source
of (B): J. Foroughi, G.M. Spinks, S. Aziz, A. Mirabedini, A. Jeiranikhameneh, G.G. Wallace, M.E.
Kozlov, R.H. Baughman, Knitted carbon-nanotube-sheath/spandex-core elastomeric yarns
for artificial muscles and strain sensing, ACS Nano 10 (10) (2016) 9129–9135.)
et al. [46] constructed hierarchically arranged helical fibers (HHFs) that re-
spond to solvent and vapor through the hierarchical and helical assembly of
aligned CNTs. The HHFs were then woven into a smart textile (Fig. 11.7A).
A copper ball with a mass of 240 mg, more than 100 times that of the smart
textile, was lifted 4.5 mm within milliseconds of spraying with ethanol.
In knitting, the yarns are kept together by loops that give a latent
potential for being easily deformable. In one example, CP polypyrrole
(PPy) was used as the active material that deforms in response to elec-
trical stimulation [48]. Foroughi et al. [47] fabricated knitted textiles
(Fig. 11.7B) based on Spandex/CNT composite yarns. Spandex fila-
ments were continuously wrapped with CNT aerogel sheets, resulting in
a highly stretchable and electrically conductive textile actuator. The ac-
tuator utilizes the thermoelasticity of the rubber copolymer segments of
the Spandex to generate contractile displacements and associated tensile
forces. Electrothermal heating of the textile actuator generates large ten-
sile contractions (up to 33%) and caused a gravimetric mechanical work
capacity up to 0.64 kJ/kg during contraction, which far exceeds that of
mammalian skeletal muscle.

11.4 Energy conversion mechanisms

Any stimulus (e.g., electricity, solvent, heating, electrochemistry, etc.) that
can create a volumetric change may be used to drive actuators. The energy
conversion mechanisms used to drive CNT yarn-based actuators are sum-
marized below.