In spite of the recent successful demonstrations of flexible and transparent film heaters, most heaters with high optical transmittance and low applied direct current （DC） voltage are silver nanowire ...（Ag NW）-based or silver grid-based. In this study, flexible and stretchable copper nanowire （Cu NW）-based transparent film heaters were fabricated through a solution-based process, in which a thin layer of hydrophobic polymers was encapsulated on the Cu NW films. The thin polymer layer protected the films from oxidation under harsh testing conditions, i.e., high temperature, high humidity, and acidic and alkaline environments. The films exhibited remarkable performance, a wide operating temperature range （up to 150 ℃）, and a high heating rate （14 ℃/s）. Defrosting and wearable thermotherapy demonstrations of the Cu NW film heaters were carried out to investigate their practicality. The Cu NW-based film heaters have potential as reliable and low-cost film heaters.
Three etchants are used to synthesize three different Ti3C2Tx (MXene) samples. The difference in chemical components, morphology and surface terminations of Ti3C2Tx and their influences on the ...conductivity, stability and flexibility are comprehensively analyzed. The underlying mechanism is investigated simultaneously. Besides, favorable annealing treatments and storage conditions are also proposed to optimize the properties of Ti3C2Tx.
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•Three typical etchants HF, LiF/HCl, TMAOH are used to synthesize three different Ti3C2Tx (MXene) samples.•The difference in chemical components, morphology and surface terminations of Ti3C2Tx are comprehensively analyzed.•Favorable annealing treatments and storage conditions are also proposed to optimize the properties of Ti3C2Tx.
Two-dimensional transition metal carbides or/and nitrides (MXenes) exhibit great development prospects in energy storage, catalysis, sensing and other fields due to their good properties. However, MXenes obtained from different etching conditions show great discrepancy on their electrical and mechanical properties, which will affect their applications to a certain degree. Unfortunately, few reports have systematically investigated such discrepancy and the underlying mechanism. Herein, three etchants and corresponding subsequent operations were used to synthesize three different Ti3C2Tx (MXene) samples. The difference in chemical components, morphology and surface terminations of Ti3C2Tx and their influences on the conductivity, stability and flexibility were comprehensively analyzed. The underlying mechanism has been investigated simultaneously. Based on this, favorable annealing treatments and storage conditions are also proposed to optimize the properties of Ti3C2Tx, which is believed of great meaning to the practical applications of Ti3C2Tx.
Copper nanowires （Cu NWs） have attracted increasing attention as building blocks for electronics due to their outstanding electrical properties and low cost. However, organic residues and oxide ...layers ubiquitously existing on the surface of Cu NWs impede good inter-wire contact. Commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, hydrogen plasma treatment at room temperature has been demonstrated to be effective for simultaneous surface cleaning and selective welding of Cu NWs at junctions. Transparent electrodes with excellent optical-electrical performance （19 ff）-sq-1 @ 90% T） and enhanced stability have been fabricated and integrated into organic solar cells. Besides, Cu NW conductors with superior stretchability and cycling stability under stretching speeds of up to 400 mm-min-＇ can also be produced by the nanowelding process, and the feasibility of their application in stretchable LED circuits has been demonstrated.
Bioelectric electrodes with low modulus and high adhesion have been intensively pursued, as they afford conformal and strong bonding at skin‐electrode interface to improve the fidelity and stability ...of electrophysiological signals. However, during detachment, tough adhesion can cause pain or skin allergy; worse still, the soft electrodes can suffer damage due to excessive stretch/torsion, hampering long‐term, dynamic, and multiple uses. Herein, a bioelectric electrode is proposed by transferring silver nanowires (AgNWs) network to the surface of bistable adhesive polymer (BAP). The phase transition temperature of BAP is tuned to be slightly below skin temperature at 30 °C. Triggered by skin heat, the BAP electrode achieves low modulus and high adhesion within seconds, allowing robust skin‐electrode interface under dry, wet, and body‐moving conditions. Ice bag treatment can dramatically stiffen the electrode and reduce the adhesion, which allows painless detachment and avoids electrode damage. Meanwhile, the AgNWs network with biaxial wrinkled microstructure remarkably promotes the electro‐mechanical stability of the BAP electrode. The BAP electrode successfully combines long‐term (7 days) and dynamic (body movements, sweat, underwater) stability, reusability (at least ten times), and minimized skin irritation during electrophysiological monitoring. The high signal‐to‐noise ratio and dynamic stability are demonstrated in the application of piano‐playing training.
A bioelectric electrode is developed by incorporating a temperature‐sensitive phase‐transition polymer and a biaxially pre‐strained AgNWs percolation network. The bioelectric electrode exhibits a quick and dramatic stiffness/adhesion switch around skin temperature, which enables stable electrophysiological monitoring in long‐term and dynamic states, and allows painless and non‐destructive detachment and reusability.
A high sensitivity and large stretchability are desirable for strain sensors in wearable applications. However, these two performance indicators are contradictory, since the former requires a ...conspicuous structural change under a tiny strain, whereas the latter demands morphological integrity upon a large deformation. Developing strain sensors with both a high sensitivity (gauge factor (GF) > 100) and a broad strain range (>50%) is a considerable challenge. Herein, a unique Ti3C2Tx MXene nanoparticle–nanosheet hybrid network is constructed. The migration of nanoparticles leads to a large resistance variation while the wrapping of nanosheet bridges the detached nanoparticles to maintain the connectivity of the conductive pathways in a large strain region. The synergetic motion of nanoparticles and nanosheets endows the hybrid network with splendid electrical–mechanical performance, which is reflected in its high sensitivity (GF > 178.4) over the entire broad range (53%), the super low detection limit (0.025%), and a good cycling durability (over 5000 cycles). Such high performance endows the strain sensor with the capability for full‐range human motion detection.
A strain sensor based on a Ti3C2Tx nanoparticle‐nanosheet hybrid network exhibits high sensitivity over the entire broad range due to the synergetic motion of nanoparticles and nanosheets and a constrained microcrack propagation mechanism. The migration of nanoparticles leads to a large resistance variation while the wrapping of the nanosheets bridges the nanoparticles and maintains the connectivity of the conductive pathways.
Abstract
A high sensitivity and large stretchability are desirable for strain sensors in wearable applications. However, these two performance indicators are contradictory, since the former requires ...a conspicuous structural change under a tiny strain, whereas the latter demands morphological integrity upon a large deformation. Developing strain sensors with both a high sensitivity (gauge factor (GF) > 100) and a broad strain range (>50%) is a considerable challenge. Herein, a unique Ti
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MXene nanoparticle–nanosheet hybrid network is constructed. The migration of nanoparticles leads to a large resistance variation while the wrapping of nanosheet bridges the detached nanoparticles to maintain the connectivity of the conductive pathways in a large strain region. The synergetic motion of nanoparticles and nanosheets endows the hybrid network with splendid electrical–mechanical performance, which is reflected in its high sensitivity (GF > 178.4) over the entire broad range (53%), the super low detection limit (0.025%), and a good cycling durability (over 5000 cycles). Such high performance endows the strain sensor with the capability for full‐range human motion detection.
A Cu nanowire （NW）/cuprous oxide （Cu2O）-based semiconductor-liquid junction solar cell with a greatly enhanced efficiency and reduced cost was assembled. The Cu NWs function as a transparent ...electrode as well as part of the Cu NWs/ Cu2O coaxial structures, which remarkably benefit the charge separation. The best solar cell reached a conversion efficiency as high as 1.92% under a simulated AM1.5G illumination, which is 106 times higher than that of cells based on fluorine-doped tin oxide and Cu2O.
Recent years have witnessed significant development of flexible strain sensors in a variety of fields. Nevertheless, the challenge of integrating a broad sensing range (>50%) with high sensitivity ...gauge factor (GF) value > 100 over the entire sensing strain in one single flexible strain sensor still exists. Herein, we prepared a flexible strain sensor based on braided graphene belts (BGBs) and dragon skin. Such a BGB strain sensor exhibits an integration of a wide sensing range (up to 55.55%) and high sensitivity (GF value > 175.16 through the entire working range). Besides, this BGB strain sensor also demonstrates a minute monitoring limit (0.01%), low hysteresis and overshoot behaviors, and reliable cycling repeatability (>6000 cycles). The SEM microscopy observations reveal that the skew angle and intersection regions of graphene belts are mainly responsible for the desirable sensing performance. Finally, the successful detection of full-range human motions, from subtle actions to vigorously joint-related movements, reflects great potential of the BGB strain sensor in the application of wearable instruments.
Recent years have witnessed the development of flexible force sensors. In this review, we summarize conductive force sensing materials appeared recently, and critically discuss the force sensing ...characteristics of conductive networks reported lately. This review aims at providing guidance for the customization of flexible force sensors.
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•We summarize some conductive force sensing materials appeared lately.•We analyse the force sensing characteristics of conductive networks.•We propose the future development trends of flexible force sensors.
Current years have witnessed the achievements of flexible force sensors, since they show great potentials in disease diagnosis, virtual reality and so forth. Conductive materials and the corresponding conductive networks are the two pivotal components that collaboratively determine the performances of flexible force sensors. Recently, some conductive force sensing materials that come into sight exhibit unique properties, but still not systematically concluded yet. Additionally, the diversity of conductive networks also has enormous effects on their force sensing performances. Regretfully, few associated reviews have summarized such response characteristics of conductive networks. In this review, initially, we summarize some conductive force sensing materials appeared recently, including conductive metal–organic frameworks, ionic deep eutectic gels, et al. Then, we discuss the force sensing features of conductive networks designed from the “Network Structure Engineering”, which contains intrinsic morphologies and arrangement configurations of conductive components. Finally, we propose the future development trends of flexible force sensors from the perspective of both conductive materials and conductive networks.
On-skin electrodes with high air permeability, low thickness, low elastic modulus, and high adhesion are essential for biomedical signal recordings, which provide data for sports management and ...biomedical applications. However, nanothickness electrodes interacting with the skin by van der Waals force can be interfered with by sweating, and elastomers with high adhesion prepared by modification are not satisfactory in terms of air permeability. Here, a dry electrode with high stretchability (598%), low elastic modulus (5 MPa), high air permeability (726 g m–2 d–1), and high adhesion (6.33 kPa) was fabricated by semi-embedding Ag nanowires into nonyl and glycerol-modified polyvinyl alcohol. Furthermore, a small amount of 40 wt % ethanol was sprayed on the skin to facilitate microdissolution of the substrate and form immediate conformability with skin texture. The dry electrodes can record high-quality electrocardiogram and electromyogram signals through a robust contact with the skin under skin deformation, with a water stream, or after running for 1 h. The film can also be served as the substrate for self-adhesive strain sensors to monitor motion with higher quality than nonadhesive polydimethylsilane-based sensors.
