The increasing demand for wearable electronic devices has made the development of highly elastic strain sensors that can monitor various physical parameters an essential factor for realizing next generation electronics. Here, we report an ultrahigh stretchable and wearable device fabricated from dry-spun carbon nanotube (CNT) fibers. Stretching the highly oriented CNT fibers grown on a flexible substrate (Ecoflex) induces a constant decrease in the conductive pathways and contact areas between nanotubes depending on the stretching distance; this enables CNT fibers to behave as highly sensitive strain sensors. Owing to its unique structure and mechanism, this device can be stretched by over 900% while retaining high sensitivity, responsiveness, and durability. Furthermore, the device with biaxially oriented CNT fiber arrays shows independent cross-sensitivity, which facilitates simultaneous measurement of strains along multiple axes. We demonstrated potential applications of the proposed device, such as strain gauge, single and multiaxial detecting motion sensors. These devices can be incorporated into various motion detecting systems where their applications are limited to their strain.

Increase in conductivity and mechanical properties of a carbon nanotube (CNT) fiber inspired by mussel-adhesion chemistry is described. Infiltration of polydopamine into an as-drawn CNT fiber followed by pyrolysis results in a direct insulation-to-conduction transformation of poly(dopamine) into pyrolyzed-poly(dopamine) (py-PDA), retaining the intrinsic adhesive function of catecholamine. The py-PDA enhances both the electrical conductivity and the mechanical strength of the CNT fibers.

Carbon nanotubes (CNTs) have received extensive attention due to their extraordinary properties in electronic conduction, [ 1 ] heat transfer, [ 2 ] and mechanical strength. [ 3 ] Materials with unparallel performance, such as super-strong, lightweight e-textiles, can be fabricated from CNTs, suggesting a future revolution in materials science. Thus, the emerging CNT technology will largely depend on the development of effective spinning and post-spinning processes to realize such unprecedented materials. Two widely implemented strategies for fabricating CNT fi bers are in-solution [4][5][6][7] and solid-state spinning techniques. The in-solution spinning of CNTs can produce continuous CNT fi bers; however, homogeneous dispersion of CNTs in the solvent is necessary for proper spinning. Moreover, the properties of the CNT fi bers strongly depend on the methods of CNT dispersion. An alternative strategy is solid-state spinning, [8][9][10][11][12][13][14][15][16][17] which allows avoidance of CNT dispersion in solvents and for various post-spinning processes to be applied with ease. Twisting, [10][11][12][13][14][15][16] densifi cation, [ 9 , 18 ] and infi ltration [ 8 , 19,20 ] are examples of post-spinning processes, and the main purpose of the spinning and post-spinning processes is to enhance the mechanical properties of CNT fi bers. Despite the effort that has been made, however, fabrication of strong CNT fi bers remains a great challenge.The strong protein-based adhesives found in marine mussel Mytilus edulis , provide an important insight into the development of post-spinning processes of CNT fi bers. The mussel secretes special adhesive foot proteins that undergo rapid solidifi cation in seawater. At a molecular level, the unusual amino acid 3,4-dihydroxy-L -phenylalanine (DOPA) found in the adhesive proteins functions as a molecule that is responsible for the solidifi cation by oxidative chemical crosslinking. [21][22][23][24] From a chemical point of view, covalent crosslinking with amines and/or catechol (a side chain of DOPA) or metal coordination are the reactions involved with DOPA, and the reactions are responsible for mechanical reinforcement of the adhesive materials of mussels. [ 25 ] Here, inspired by the molecular mechanics of mussel adhesive formation, we demonstrate a new postspinning process for the fabrication of CNT fi bers ( Figure 1 a,b). By infi ltration of mussel-mimetic adhesive polymers and curing through thermal and metal oxidation, we demonstrate an increase in the tensile strength of CNT fi bers by up to 470%. The study described suggests a general post-spinning approach for enhancement of the mechanical properties of CNT fi bers prepared by various spinning techniques.Vertically well-aligned CNT arrays were grown on Fe-catalystimmobilized (1.7-nm-thick) silicon substrates by plasmaenhanced chemical vapor deposition. Methane (CH 4 ) was used as the carbon source to synthesize CNTs, with argon (Ar), hydrogen (H 2 ), and oxygen (O 2 ) carrier gases. In the presence of Ar gas fl ow...

No abstract