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(A) A fiber is stretched; then the fiber is “NTS” wrapped; then the “NTS”-wrapped stretched fiber is released. The shortening of the “NTS”-wrapped fiber causes hierarchical buckling of the formerly smooth “NTS” wrapping. The buckling deformations are shown in B, C and D
FROM:
Z.F. Liu, S. Fang, F.A. Moura, J.N. Ding, N. Jiang, J. Di, M. Zhang, X. Lepro, D.S. Galvao, C.S. Haines, et al,
“Hierarchically buckled sheath-core fibers for superelastic electronics, sensors, and muscles”, Science, Vol. 349, No. 6246, pp 400-404, 24 July 2015, DOI: 10.1126/science.aaa7952
ABSTRACT: Superelastic conducting fibers with improved properties and functionalities are needed for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%) sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in the fiber direction on stretched rubber fiber cores. The resulting structure exhibited distinct short- and long-period sheath buckling that occurred reversibly out of phase in the axial and belt directions, enabling a resistance change of less than 5% for a 1000% stretch. By including other rubber and carbon nanotube sheath layers, we demonstrated strain sensors generating an 860% capacitance change and electrically powered torsional muscles operating reversibly by a coupled tension-to-torsion actuation mechanism. Using theory, we quantitatively explain the complementary effects of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation and electronic properties.
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