High-performance structure of a coil-shaped soft-actuator consisting of polymer threads and carbon nanotube yarns

We fabricated thermally driven metal-free soft-actuators consisting of poly(ethylene terephthalate) (PET) threads as the actuator and carbon nanotube (CNT) yarns as the heating source. The mechanical force, displacement, and response behavior of various structures of the coil-shaped soft-actuators were characterized. The actuation performance of the soft-actuators containing a homogeneous arrangement of PET threads and CNT yarns in their cross-sectional profile was the highest. The results of the calculations based on the heat diffusion equations indicated that inhomogeneous heat generation in the soft-actuator causes parts of the actuator to remain unheated and this interferes with the mechanical motions. Homogeneous thermal distribution in the soft-actuators, namely, the use of a multifilament structure, yields the highest performance in terms of the mechanical force and displacement.