Most applications that require rotational positioning and high torque generation for mechanical performance are often non-compact with a complex design that is not ideal for nanotechnological applications. Twist-spun carbon nanotube (CNT) yarn can serve as an actuation for high-performance motion systems like artificial muscles that require torsional rotation in addition to bending and contraction and micromechanical devices. Their nanoscale dimension and aspect ratio is attractive for torsional sensing. Torsional acceleration in CNT yarn can be driven in both directions for conversion of mechanical energy to electrical energy. This can find application in sensors that generate electrical signals through applied torsional rotation.
The effect of twist on the elasticity, yarn strength, strain to failure and piezoresistivity is discussed. CNT yarns with low twist angle (10-20o) was produced to compare with a medium to high twisted yarns (37-45o). The lowly twisted CNT yarn had a lower breaking strength and elongation at rupture but higher rigidity while the highly twisted CNT yarn showed higher ultimate breaking strength and higher strain to failure but lower stiffness modulus. The decrease in electrical resistance upon application of torsional loading to the CNT yarns demonstrate that applied twist increases fiber compaction, resulting in increased electrical contact between nanotubes and a negative piezoresistance. The piezoresistive response of highly twisted yarn is however lower than that of the low twisted thread leading to conclusion of twist being of mechanical advantage due to its effect on intertube slippage and less effective in strain sensing applications.