Fig. 1.

Schematic illustration and morphological information of supercoiled fibres. a Schematic illustration of highly twisted spandex@carbon nanotube (CNT) fibre, consisting of first-coils and supercoils. Inset shows a schematic of microscale buckled surface. Scanning electron microscopy (SEM) images for b microscopic scaled buckles formed on the surface of spandex@CNT fibre relaxed from pre-strain (scale bar = 15 μm), and c its magnification showing uniaxially aligned CNT bundles (scale bar = 5 μm). SEM images for d noncoiled, e first coiled, and f supercoiled spandex@CNT fibres, showing subsequent structure transformations as the number of twists increases (scale bars for d, e, and f are 200 μm). Inset images from e and f show fibre transformations from noncoiled fibre into first coil, and from first coil into supercoil, respectively. The arrows indicate the propagation direction of coil formation. g Measured length-normalised resistance changes and fibre length contraction versus number of inserted twists until full supercoiling (R(ε) is the resistance of fibre at the stretched state and L₀ is the length of fibre at the initial state). Photograph of h free-standing state, double-helix structured, supercoiled fibre, and optical images of i its magnification (scale bar = 1 mm), j 3.5-cm-long, six-woven supercoiled spandex@CNT fibres into a commercial mock rib-structured textile, and k 20 mm-long, 7 mm-wide supercoil textile consisting of 27 spandex@CNT fibres