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In this work, transmission electron microscopy (TEM) was applied to study single-walled carbon nanotube (SWCNT) dispersion states in aqueous solutions at nanoscale, and a method based on selected-area electron diffraction patterns was developed to quantitatively describe the internal SWCNT alignment across a whole fiber. Moreover, the SWCNT bundle size and pore defects were also evaluated by high-resolution TEM. It was found that the SWCNT bundle size increased from approximately 15 to 40 nm as its mass concentration increased from 0.4% to 1.0% in the spinning dope, which then influenced the SWCNT bundle size in the final fibers. Meanwhile, the degree of SWCNT alignment in the fiber increased initially and then decreased monotonically with the increased concentration. The effects of spinning needle size and length on the mechanical performance of the fibers were also discussed. The combination of the nano-structural characterizations of the spinning dopes and the final fibers sheds some light on the development of high-performance CNT fibers.

A new approach for making carbon nanotube (CNT) films that are both strong and tough is detailed in this paper. Aqueous dispersions of long CNTs were first obtained by dispersing CNT arrays with heights of about 200 μm in deionized water with the help of polyvinylpyrrolidones (PVPs) and polydopamines (PDAs). CNT films were then obtained by vacuum-assisted filtration of CNT dispersions. The tensile strength and toughness of the composite films can be as high as 143.5 MPa and 5.0 MJ/m3, respectively, which was 330.7% and 213.8% higher than CNT films made without using PVPs and PDAs. The underlying mechanism of PVPs and PDAs induced CNT film strengthening and toughening was revealed through preliminary molecular dynamics simulations, which indicated that the hydrogen bonds between the PVPs and PDAs enhanced the strength of the film, and these bonds can cyclically break and reform, making CNT films tougher. The strategy proposed here can also be applied to making other nano-materials based strong and tough macro-assemblies.

Stretchable conductive fibers have attracted significant attention due to their ability to be directly woven into or stitched onto fabrics, making them ideal for use in the design of integrated wearable strain sensors. Here, we report on a highly stretchable multi-walled carbon nanotube (MWCNT)/Thermoplastic Polyurethane (TPU) fiber produced via a wet spinning process. The effects of MWCNT content and alignment on the structural, mechanical, electrical and strain-sensing properties of the composite fibers were investigated. The highest conductivity (6.77 S cm−1), tensile strength (28 MPa) and maximum elongation at break (565%) were obtained by controlling the MWCNT content. Gauge factor (GF) values were also affected by the content and MWCNT alignment in the composite fibers, as these parameters determine the change in the effective contact area and number of conductive paths available during stretching. The well-aligned MWCNT/TPU fiber showed a high GF value of 5200. Wearable strain sensors capable of obtaining real-time mechanical feedback for various human motion detections with different GFs and working strain ranges could be realized by controlling the MWCNT concentrations in the TPU matrix.

The tensile mechanical properties of carbon nanotube (CNT) fiber, which is a one-dimensional assembly of ultra-strong CNTs, are still far short of our expectations. This is mainly due to their high porosity and relatively weak intertube load transfer efficiency. Previous studies have demonstrated that the fiber strength can be enhanced by the infiltration of polymer chains into the fiber. In this work, polyvinyl alcohol (PVA) was pre-infiltrated into loosely packed CNT ribbons, and the composite ribbons were then densified into the fiber form. This enabled a homogeneous dispersion of polymer chains within the CNT fibers. To enhance the mechanical properties of the CNT/PVA composite fibers, isothermal crystallization and ultrasonic treatments were implemented to increase the crystallization of PVA in the ribbon, and the composite fibers were hot-stretched to improve the alignment of both CNTs and PVA chains within the fibers. It was found that the tensile strength and modulus of the final composite fiber were 210% and 193.6% higher than those of the pristine CNT fiber. The structural evolution during these treatments and the mechanism of fiber strengthening were systematically investigated.

Easy shapeable highly porous and robust three dimensional (3D) nano-carbon architectures (3D NCA) are crucial for the practical applications of electrochemical energy storage devices. Here, a facile easy shapeable nitrogen-doped graphene coated 3D NCA exhibiting an ultra-high specific surface area, remarkable robustness, and excellent aqueous wettability is reported. A 3D single-walled carbon nanotube (SWCNT) hydrogel composed of isolated SWCNTs is first prepared, and then a thin polydopamine (pDA) layer is uniformly coated onto the fabricated 3D SWCNT hydrogel via an in situ polymerization of dopamine. A nitrogen-doped graphene-coated 3D NCA is obtained via pyrolysis of the pDA-coated 3D NCA. By decorating this highly porous nitrogen-doped 3D NCA onto helical micro carbon fibers, a highly stretchable (∼100% strain) wire-type supercapacitor (WTSC) is fabricated. The areal specific power and energy density of the WTSC are determined to be 2.59 mW cm−2 and 1.1 μWh cm−2, respectively. These values are remarkably larger than those previously reported WTSCs. Moreover, our WTSC maintains more than 91% of its capacitance after 10,000 stretch-release cycles at tensile strains of up to 50%. The combination of the easy shapeable, robust and highly porous nitrogen-doped 3D NCA paves a new way for the development of high-performance wearable textile-based energy devices.

Solution spinning is the most promising approach of fabricating continuous carbon nanotube (CNT) fibers in industrial scale. Understanding the relationship between processing, structures and properties is of great significance for the optimization and application of solution spun CNT fibers. In this study, the influence of dispersion time on the microstructural and mechanical properties of CNT solutions and their spun fibers were systematically investigated. It has been found that with the increasing of dispersion time, CNT bundle size and length decreased, resulting in improved homogeneity of CNT dispersions, while the mechanical properties of CNT fibers increased firstly and then decreased. The orientation of CNTs along the fiber axis was found undesirable when CNTs were either too short or too long in the solution. This study provided a general guidance for fabricating high-performance fibers from one-dimensional nanomaterials .

Here, we report a novel highly sensitive wearable strain sensor based on a highly stretchable multi-walled carbon nanotube (MWCNT)/Thermoplastic Polyurethane (TPU) fiber obtained via a wet spinning process. The MWCNT/TPU fiber showed the highest tensile strength and ultra-high sensitivity with a gauge factor (GF) of approximately 2800 in the strain range of 5–100%. Due to its high strain sensitivity of conductivity, this CNT-reinforced composite fiber was able to be used to monitor the weight and shape of an object based on the 2D mapping of resistance changes. Moreover, the composite fiber was able to be stitched onto a highly stretchable elastic bandage using a sewing machine to produce a wearable strain sensor for the detection of diverse human motions. We also demonstrated the detection of finger motion by fabricating a smart glove at the joints. Due to its scalable production process, high stretchability and ultrasensitivity, the MWCNT/TPU fiber may open a new avenue for the fabrication of next-generation stretchable textile-based strain sensors.

Textile-based humidity sensors can be an important component of smart wearable electronic-textiles and have potential applications in the management of wounds, bed-wetting, and skin pathologies or for microclimate control in clothing. Here, we report a wearable textile-based humidity sensor for the first time using high strength (∼750 MPa) and ultratough (energy-to-break, 4300 J g–1) SWCNT/PVA filaments via a wet-spinning process. The conductive SWCNT networks in the filaments can be modulated by adjusting the intertube distance by swelling the PVA molecular chains via the absorption of water molecules. The diameter of a SWCNT/PVA filament under wet conditions can be as much as 2 times that under dry conditions. The electrical resistance of a fiber sensor stitched onto a hydrophobic textile increases significantly (by more than 220 times) after water sprayed. Textile-based humidity sensors using a 1:5 weight ratio of SWCNT/PVA filaments showed high sensitivity in high relative humidity. The electrical res...

Many stretchable conductive composite fibers exhibit high elongation at break, but most of them do not have a large workable strain range towing to the low conductivity when used as strain sensors. In this paper, we fabricated a highly conductive silver nanowire (Ag NW)/multi-walled carbon nanotube (MWCNT)/thermoplastic polyurethane (TPU) fiber via a wet-spinning process to improve the workable strain range of composite fibers. TPU was used as a matrix material to introduce superior stretchability. MWCNTs act as sensing elements and Ag NWs were used to increase conductivity. We investigated the effect of Ag NW content on the mechanical, electrical, and strain-sensing performance of the fiber-type strain sensors. The optimal content of Ag NWs extended the workable strain range as higher as 254% with an electrical conductivity of 0.803 S/cm. A weight-to-strain cloth sensor was assembled by writing Ag NW/MWCNT/TPU fibers in the coagulation solution. Furthermore, such composite fiber can be free-written into any designed pattern, which can be used to prepare fiber-based devices.

The development of fiber-based smart electronics has provoked increasing demand for high-performance and multifunctional fiber materials. Carbon nanotube (CNT) fibers, the 1D macroassembly of CNTs, have extensively been utilized to construct wearable electronics due to their unique integration of high porosity/surface area, desirable mechanical/physical properties, and extraordinary structural flexibility, as well as their novel corrosion/oxidation resistivity. To take full advantage of CNT fibers, it is essential to understand their mechanical and conductive properties. Herein, the recent progress regarding the intrinsic structure-property relationship of CNT fibers, as well as the strategies of enhancing their mechanical and conductive properties are briefly summarized, providing helpful guidance for scouting ideally structured CNT fibers for specific flexible electronic applications.

Magnetic nanocomposite fibers are a topic of intense research due to their potential breakthrough applications such as smart magnetic-field-response devices and electromagnetic interference (EMI) shielding. However, clustering of nanoparticles in a polymer matrix is a recognized challenge for obtaining a property-controllable nanocomposite fiber. Another challenge is that the strength and ductility of the nanocomposite fiber decrease significantly with increased weight loading of magnetic nanoparticles in the fiber. Here, we report high-strength single-walled carbon nanotube (SWNT)/permalloy nanoparticle (PNP)/poly(vinyl alcohol) multifunctional nanocomposite fibers fabricated by wet spinning. The weight loadings of SWNTs and PNPs in the fiber were as high as 12.0 and 38.0%, respectively. The tensile strength of the fiber was as high as 700 MPa, and electrical conductivity reached 96.7 S m(-1). The saturation magnetization (Ms) was as high as 24.8 emu g(-1). The EMI attenuation of a fabric woven from the prepared fiber approached 100% when tested with electromagnetic waves with a frequency higher than 6 GHz. The present study demonstrates that a magnetic-field-response device can be designed using the fabricated multifunctional nanocomposite fiber.