Wide‐Range Tunable Dynamic Property of Carbon‐Nanotube‐Based Fibers

A carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the nonzero loss tangent (>0.028–0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fiber's tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by a high packing density and the formation of covalent polymer cross‐links within the fiber. The CNT/bismaleimide composite fiber exhibits the smallest loss tangent, nearly the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi‐ply CNT yarn, the interfiber friction and sliding tendency obviously influence the yarn's damping performance, and the loss tangent can be tuned within a wide range, similar to carbon fibers, nylon yarns, or cotton yarns. The wide‐range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems.     

Mechanical Peeling of Free‐Standing Single‐Walled Carbon‐Nanotube Bundles

An in situ electron microscopy study is presented of adhesion interactions between single‐walled carbon nanotubes (SWNTs) by mechanically peeling thin free‐standing SWNT bundles using in situ nanomanipulation techniques inside a high‐resolution scanning electron microscope. The in situ measurements clearly reveal the process of delaminating one SWNT bundle from its originally bound SWNT bundle in a controlled‐displacement manner and capture the deformation curvature of the delaminated SWNT bundle during the peeling process. A theoretical model based on nonlinear elastica theory is employed to interpret the measured deformation curvatures of the SWNTs and to quantitatively evaluate the peeling force and the adhesion strength between bundled SWNTs. The estimated adhesion energy per unit length for each pair of neighboring tubes in the peeling interface based on our peeling experiments agrees reasonably well with the theoretical value. This in situ peeling technique provides a potential new method for separating bundled SWNTs without compromising their material properties. The combined peeling experiments and modeling presented in this paper will be very useful to the study of the adhesion interactions between SWNTs and their nonlinear mechanical behaviors in the large‐displacement regime.     

Magnetization Dynamics of an Individual Single‐Crystalline Fe‐Filled Carbon Nanotube

The magnetization dynamics of individual Fe‐filled multiwall carbon‐nanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single‐crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin‐wave transport seen in BLS indicate, however, that the Fe filling is not a single straight piece along the length. Therefore, a stepwise cutting procedure is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 400 nm long single‐crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting FeCNTs as appealing candidates for spin‐wave transport in magnonic applications.     

Thread‐like Supercapacitors Based on One‐Step Spun Nanocomposite Yarns

Thread‐like electronic devices have attracted great interest because of their potential applications in wearable electronics. To produce high‐performance, thread‐like supercapacitors, a mixture of stable dispersions of single‐walled carbon nanotubes and conducting polyaniline nanowires are prepared. Then, the mixture is spun into flexible yarns with a polyvinyl alcohol outer sheath by a one‐step spinning process. The composite yarns show excellent mechanical properties and high electrical conductivities after sufficient washing to remove surfactants. After applying a further coating layer of gel electrolyte, two flexible yarns are twisted together to form a thread‐like supercapacitor. The supercapacitor based on these two yarns (SWCNTs and PAniNWs) possesses a much higher specific capacitance than that based only on pure SWCNTs yarns, making it an ideal energy‐storage device for wearable electronics.     

Electronic‐Type‐ and Diameter‐Dependent Reduction of Single‐Walled Carbon Nanotubes Induced by Adsorption of Electron‐Donor Molecules

The adsorption of the organic donor molecules tetrakis(dimethylamino)ethylene (TDAE) and cobaltocene (CoCp₂) on high‐pressure CO decomposition (HiPco) single‐walled carbon nanotubes (SWNTs) is investigated using density functional theory (DFT), optical absorption, and Raman spectra methods. The selective reduction of SWNTs according to the electronic type and diameter of SWNTs is revealed. The reduction rate decreases in the order: metallic SWNTs ≥ large‐diameter semiconducting SWNTs > small‐diameter semiconducting SWNTs.