Hierarchically buckled sheath-core fibers for superelastic electronics, sensors, and muscles

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.

Advanced carbon materials for flexible and wearable sensors

“…Generally, flexible polymers, such as polydimethylsiloxane (PDMS) [50,[90][91][92][93][94][95], ecoflex [28,96,97], polyurethane (PU) [98,99], polyethylene terephthalate (PET) [84,100,101], polyimide (PI) [102,103] and rubber [104,105], are commonly used as the substrates/matrix for the fabrication of sensors due to their excellent flexibility, good thermal and chemical stability. Active materials, such as CNTs [28,[106][107][108][109][110], graphene (including rGO) [83,84,90,100,[111][112][113], metal nanoparticles and nanowires [50,53], semiconductors [114,115], conductive polymers [46,48], and their hybrid structures [116,117], have been intensively investigated. Typically, the sensors based on nanoparticles can achieve high GFs [58].…”

Ultrastretchable Fiber Sensor with High Sensitivity in Whole Workable Range for Wearable Electronics and Implantable Medicine

“…Buckled structures are usually used to fabricate stretchable conductors with stable conductance during deformation, in which conducting thin layers are deposited on the surface of a prestretched substrate followed by stretch‐release 18, 19, 20. Here, we report a novel buckled sheath–core fiber‐based ultrastretchable strain sensor and demonstrate its outstanding sensing performance in whole workable range.…”

“…Here, we report a novel buckled sheath–core fiber‐based ultrastretchable strain sensor and demonstrate its outstanding sensing performance in whole workable range. The ultrastretchable fiber sensor with a buckled sheath was designed and fabricated by wrapping an ultralight multiwalled carbon nanotubes/thermal plastic elastomer (MWCNT/TPE) composite film (NTTF) around a prestretched TPE elastic rubber fiber and then releasing the stretching force,18, 21, 22which is denoted as NTTF n @fiber, where n indicates the number of NTTF layers of the sheath. The 1D fiber strain sensor has a large workable strain range (>1135%), compatible elastic modulus with human skin (≈140 kPa), fast response time (≈16 ms), high sensitivity in whole workable range (GF of 21.3 over a 0–150% strain range and 34.22 over a 200–1135% strain range), and repeatability and stability (20 000 cycles load/unload test).…”

Double‐Twisted Conductive Smart Threads Comprising a Homogeneously and a Gradient‐Coated Thread for Multidimensional Flexible Pressure‐Sensing Devices

“…[29,30] Their excellent flexibility, high sustainability, light weight, and comfort have favored their use in flexible circuits, [31] textile-like batteries or supercapacitors, [32] fiber-based solar cells or nanogenerators, [33] woven organic light-emitting diodes, [34] and strain sensors.…”