Triboelectric nanogenerators (TENGs) have demonstrated their promising potential in biomotion energy harvesting. A combination of the TENG and textile materials presents an effective approach toward smart fabric. However, most traditional fabric TENGs with an alternating current (AC) have to use a stiff, uncomfortable, and unfriendly rectifier bridge to obtain direct current (DC) to store and supply power for electronic devices. Here, a DC fabric TENG (DC F-TENG) with the most common plain structure is designed to harvest biomotion energy by tactfully taking advantage of the harmful and annoying electrostatic breakdown phenomenon of clothes. A small DC F-TENG (1.5 cm × 3.5 cm) can easily light up 416 serially connected light-emitting diodes. Furthermore, some yarn supercapacitors are fabricated and woven into the DC F-TENG to harvest and store energy and to power electronic devices, such as a hygrothermograph or a calculator, which shows great convenience and high efficiency in practice. This low-cost and efficient DC F-TENG which can directly generate DC energy without using the rectifier bridge by harvesting energy from unhealthy electrostatic breakdown has great potential as a lightweight, flexible, wearable, and comfortable energy-harvesting device in the future.

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As a wearable device, highly sensitive and stretchable strain sensors should be integrated to monitor various daily actions, which include large- and small-scale strains, such as jumping, running, heartbeat, and pulse. At present, the method of preparing strain sensors is mainly to impregnate or load materials like graphene, carbon nanotube, and their union products on elastic substrates to obtain highly sensitive characteristics. Both well-known carbon-based and other single-dimensional nanomaterials do not have high flexibility and conductivity, which limits the improvement of sensitivity. However, a novel material MXene Ti3C2T x has a two-dimensional (2D) sheet structure, which allows for higher electron and ion transmission rates. In addition, it is easier to be combined with other nanomaterials as a nanosubstrate, greatly improving malleability. Hence, we creatively prepared zero-dimensional (0D)–one-dimensional (1D)–2D multi-dimensional nanomaterials, which designed 0D silver nanoparticles (AgNPs) loaded on 2D MXene nanosheets and compounded with 1D silver nanowires (AgNWs). The method improves the elasticity and conductivity of traditional single-dimensional materials, wherein AgNPs built a bridge between AgNWs and MXene, which ensures continuity and a high gauge factor even at a large strain (200%) of yarn. The composite yarn strain sensor has a remarkably high strain and sensitivity, effectively monitoring the large and small deformations of various parts of the human body, whose fabric can be an electrothermal device. It has vital inspiration for the development of intelligent textiles, which would be used in medical devices, artificial skin, and other wearable fields.

The main content dealt with in the paper is to make a theoretical analysis of the contour diameter of auxetic yarn under tension, which expands transversely under axial tension. The auxetic yarn is designed by two components, that is, a core filament and a wrap filament. Compared with the wrap filament, the core filament is thicker, softer and much more extensible. In the initial status, the core filament is straight in the center of the auxetic yarn and the wrap filament wraps the core filament helically in a certain helical angle. Based on theoretical analysis, the formula of negative Poisson's ratio of stretched auxetic yarn is obtained. It is found that the value of Poisson's ratio is related to axial strain, helical angle and the diameter ratio of the core filament to the wrap filament. An applied example is presented to verify the Poisson's ratio value-strain curve of auxetic yarn. In order to better investigate effects on negative Poisson's ratio, the effect of different parameters of yarn, including mesh size, diameter ratio, tensile modulus and helical angle of the wrap filament, is investigated using finite element analysis based on ABAQUS software to analyze the negative Poisson's ratio of auxetic yarn when stretched. It verified that yarn spun by two different components produced a negative Poisson's ratio effect under tension and structure parameters of auxetic yarn significantly affected negative Poisson's ratio values. It is expected that this study could help us understanding the deformation mechanism of auxetic yarn under axial tension load.

Auxetic yarn was successfully produced by a wrap filament and a core filament based on a ring-spinning system, which showed an auxetic effect when stretched, that is, expanding transversely under tension. Yarns were spun by different structural parameters of the core filament and the wrap filament, including diameter ratio, helical angle and tensile modulus of the wrap filament. Corresponding tensile tests were utilized to analyze the effects of structural parameters and performance on outer contour deformation of auxetic yarn. Experimental results showed that the outer contour of auxetic yarn expanded transversely under tension and there existed significant negative Poisson's ratio values in the Poisson's ratio-strain curve, and it was found that the auxetic effect became more observable with a higher diameter ratio of the core filament to the wrap filament, and lower helical angle and larger tensile modulus of the wrap filament. Moreover, compared with theoretical results by theoretical modeling in Part I, good relations of Poisson's ratio-strain curves were obtained between experimental and theoretical results. This proves the effectiveness of spinning auxetic yarn by selecting reasonable components of yarn and it is feasible to design yarn with a negative Poisson's ratio effect.