active materials utilized in energy storage suffer from poor elasticity or relatively low electrochemical performance. In previous studies, three major stretchable structures have been proposed: coiled fiber structure, [6][7][8] wavy structure, [5,9,10] and islandbridge structure. [11][12][13] The active materials applied in these structures should be easily handled and tough. For use in wavy and island-bridge structures soft materials are required. Coating, transferring, in situ deposition, or polymerization of active materials onto a stretchable substrate such as fabric, polymer, and paper have been devised for the electrodes of energy storage and conversion devices; but mostly declaring a low elasticity. [14,15] A fiber-based or wire-shaped device can be easily integrated into stretchable yarns or fabrics to fulfill a more practical demand of wearable energy storage, conversation, or transition in our daily life. The electrochemical property and stretchability both play a vital role in the fiber-based supercapacitors and batteries. [16][17][18] Carbon nanotubes (CNTs) are widely used electrode materials that possess extraordinary physical and chemical properties, and they have also been verified to assemble into fiber formation by using solid-state spun or wet-spun techniques. [19] Fibers formed by pristine CNT have been demonstrated with high electrical conductivity and superior mechanical properties, although the intrinsic electrochemical performances of CNT fibers are not outstanding enough. [20][21][22][23] A possible explanation of this behavior lies in the strong interaction between carbon nanotubes, which, while increasing the packing density inside fibers, does not allow high ion accessibility. To reduce the dense stacking, CNT/graphene composites have been proposed and fabricated to increase inner porosity. [24,25] On the other hand, coiled structure and elastic polymer fibers have been reported previously as the most popular approach or material to enhance the stretchability of fibers and films, which have been incorporated with various active materials such as carbon nanomaterials (e.g., nanotubes, graphene), metal oxide nanoparticles, and conductive polymers. [6,15,[26][27][28] The reported coiled fiber supercapacitor only afforded up to a strain of 150% to maintain its performance, [6] although the capacitance could be achieved as high as 382 mF cm −2 . [28] Coincidentally, the pseudocapacitance material, deposited carbon nanotube sheets wrapped coaxial elastic fiber, demonstrated a high specific capacitance as well as a strain of 400% without damages to the properties. [27] In this paper, we explore a novel approach to fabricate nanostructured carbon nanotube/graphene/conducting polymer The demands for wearable technologies continue to grow and novel approaches for powering these devices are being enabled by the advent of new electromaterials and novel fabrication strategies. Herein, a novel approach is reported to develop superelastic wet-spun hybrid carbon nanotube graphene fibers followed by e...

Cushioning materials generally absorb kinetic mechanical energy under compression actions at a relatively constant stress over a large range of displacement. However, cushioning materials widely used today are polyurethane (PU) foams with low moisture transmission. As a new class of three-dimensional textile structures, warp-knitted spacer fabrics not only have much better moisture transmission property than PU foams, but also have the similar cushioning performance if appropriate structural parameters are adopted. This paper reports an experimental study on the compression behavior of a series of warp-knitted fabrics made for cushioning applications. These fabrics were produced on a double-needle bar warp knitting machine of gauge 18 by varying different structural parameters including spacer yarn inclination angle and fineness, fabric thickness, and outer layer structure. Both the compression stress-strain curves and energy efficiency diagrams from the testing results were used to analyze the compression behavior of these fabrics and the effect of each structural parameter. The results indicate that warp-knitted spacer fabrics are an ideal class of the energy absorbers for cushioning applications and their energy-absorption capacity can easily be tailored to meet specific end-use requirements by simply varying their structural parameters with the help of efficiency diagrams.

This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics developed for human body protections. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel warp knitting machine by varying their structural parameters, including spacer monofilament inclination and fineness, fabric thickness, and surface layer structure. A drop-weight impact tester was used to test these fabrics with predefined impact energy. The impact process of a typical spacer fabric was analyzed based on its impact contact force-displacement curve, energy absorbed-contact force curve and transmitted force-time curve. The effects of the structural parameters on the impact compressive behavior of the warp-knitted spacer fabrics were also discussed. The relationship between the peak transmitted force and peak contact force was established for these fabrics. The study shows that the warp-knitted spacer fabrics can be used as a type of effective material for human body protection due to their high energy absorption capacity and reduction of the contact peak force. The study also shows that all the structural parameters significantly affect the impact compressive behavior of the warp-knitted spacer fabrics in terms of peak contact force, peak transmitted force, and energy absorbed at different impact compressive stages. According to the results obtained, the warp-knitted spacer fabrics studied can reduce about 33.16% of the peak contact force.

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Wearable energy storage devices are of practical interest, but few have been commercially exploited. Production of electrodes with extended cycle life, as well as high energy and power densities, coupled with flexibility, remains a challenge. Herein, we have demonstrated the development of a high-performance hybrid carbon nanotube (CNT) fiber-based supercapacitor for the first time using conventional wet-spinning processes. Manganese dioxide (MnO) nanoflakes were deposited onto the as-prepared CNT fibers by electrodeposition to form highly flexible nanocomposites fibers. As-prepared fibers were characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It was found that the specific capacitance was over 152 F g (156 F cm), which is about 500% higher than the multi-walled carbon nanotube/MnO yarn-based supercapacitors. The measured energy density was 14.1 Wh kg at a power density of 202 W kg. These values are 232% and 32% higher than the energy density and power density of MWNT/MnO yarn-based supercapacitor, respectively. It was found that the cyclic retention ability was more stable, revealing a 16% increase after 10 000 cycles. Such substantial enhancements of key properties of the hybrid material can be associated with the synergy of CNT and MnO nanoparticles in the fiber structure. The use of wet-spun hybrid CNT for fiber-based supercapacitors has been demonstrated.

This paper reports the development of a hexagon resistance model, based on the loop structure of a plain weft knitted fabric. This model is capable of describing the electromechanical properties of conductive knitted elastic fabrics. Based on the relationship between the resistance and the load on the fabric under biaxial extension, the equivalent resistance of the fabric was obtained by solving the circuit network equations. It was found that the circuit network is a multiple circuit parallel to the wale direction whereas it is in series along the course direction. And Holm's electrical contact theory is used to calculate the relationship between the contact resistance and the contact force in an elastic fabric sensor. The contact load and deformation between two knitting loops are calculated using the classical knitted fabric mechanics model of Kawabata and Popper.

Wearable sensors are increasingly used in smart garments for detecting and transferring vital signals and body posture, movement and respiration. Existing fabric strain sensors made from metallized yarns have low sensitivity, poor comfort and low durability to washing. Here we report a knitted fabric strain sensor made from a cotton/stainless steel (SS) fibre blended yarn which shows much higher sensitivity than sensors knitted from metallized yarns. The fabric feels softer than pure cotton textiles owing to the ultrafine stainless steel fibres and does not lose its electrical property after washing. The reason for the high sensitivity of the cotton/SS knitted fabric sensor was explored by comparing its sensing mechanism with the knitted fabric sensor made from metallized yarns. The results show that the cotton/SS yarn-to-yarn contact resistance is highly sensitive to strain applied to hooked yarn loops.

An optimization design simulating the electro-mechanical property of the conductive elastic knitted fabric is built based on a loops structure under biaxial extensions. A computer program can give the fabric equivalent resistance, which is obtained by solving the circuit network equations. So, it can simplify the computational process immensely. In order to simplify the calculation of the contacting forces on the overlapped yarns, two hooked yarns are used to represent the loop configurations. From the theoretical analysis and experimental investigations, it is found that the resistance changing due to the yarn segment transfer is the key factor for the sensitivity of elastic fabric sensors. This makes the resistance linear increasing with the strain increasing. Analysis of the experimental results show that change in the resistance of a fabric sensor due to the contact resistance has a minor contribution to the sensitivity of the sensor in the large-strain regime. Also, the fabric structure and the yarn elongating affect the characteristics of the fabric sensor.