A soft, fatigue-free, and self-healable ionic elastomer via the synergy of skin-like assembly and Bouligand structure.

Soft ionic elastomers that are self-healable, fatigue-free, and environment-tolerant are ideal structural and sensing materials for artificial prosthetics, soft electronics, and robotics to survive unpredictable service conditions. However, most synthetic strategies failed to unite rapid healing, fatigue resistance, and environmental robustness, limited by their singular compositional/structural designs. Here, we present a soft, tough, fatigue-resistant, and self-healable ionic elastomer (STFSI elastomer), which fuses skin-like binary assembly and Bouligand helicoidal structure into a composite of thermoplastic polyurethane (TPU) fibers and a supramolecular ionic biopolymer. The interlocked binary assembly enables skin-like softness, high stretchability, and strain-adaptive stiffening through a matrix-to-scaffold stress transfer. The Bouligand structure contributes to superhigh fracture toughness (101.6 kJ m-2) and fatigue resistance (4937 J m-2) via mechanical toughening by interlayer slipping and twisted crack propagation path. Besides, the STFSI elastomer is self-healable through a "bridging" method and environment-tolerant (-20 ˚C ~ 60 ˚C, strong acid/alkali, saltwater). To demonstrate the versatile structural and sensing applications, we showcase a safety cushion with efficient damping and suppressed rebounding, and a robotic sensor with excellent fatigue crack tolerance and instant sensation recovery upon cutting-off damage. Our presented synthetic strategy is generalizable to other fiber-reinforced tough polymers for applications involving demanding mechanical/environmental conditions.

Synthesis of Metal/Bimetal Nanowires and Their Applications as Flexible Transparent Electrodes.

As a potential alternative to indium oxide (ITO), metal nanowire transparent conductive electrodes (TCEs) have attracted more and more attention. Here, a facile method that can be applied to the synthesis of a variety of metal/bimetallic nanowires has been proposed. Metal/bimetallic nanowires synthesized through this method show high aspect ratios and great dispersibility, which makes them ideal building blocks for transparent electrodes. The synthesis mechanism is discussed in-depth to give a theoretical basis of morphology control of metal nanostructures in organic synthesizing systems. TCEs with high flexibility, excellent optical-electrical performance as well as outstanding anti-thermal and anti-moisture stability are constructed. To the best of our knowledge, this is the first work on synthesizing multiple metal/bimetallic nanowires through one method.

A long-term oxidation barrier for copper nanowires: graphene says yes.

Copper nanowires (Cu NWs) hold great promise for the fabrication of low-cost transparent electrodes. However, the instability of Cu NWs has limited their application into commercial devices. Herein, CVD-grown graphene is transferred onto Cu NW films and the stability of the hybrid films over long time scale under different conditions is investigated systematically. The results reveal that the graphene-Cu NW films can maintain their efficacy (R/R0 < 2) after 180 days of exposure in an ambient atmosphere. Furthermore, a two-step oxidation kinetic mechanism of Cu NWs can be proposed by using Raman and X-Ray photoelectron spectroscopy. The protecting mechanism of graphene on Cu NW films is disclosed to preventing the oxygen species permeation, decelerating the oxidation from Cu to Cu2O and hindering the oxidation of Cu2O to CuO. These results are of referring significance to make metal nanowire based transparent electrodes with both high optical-electrical performance and excellent stability.

A symmetrical bi-electrode electrochemical technique for high-efficiency transfer of CVD-grown graphene.

Graphene transfer is a critical process in the journey from CVD-grown graphene to device application. The current transfer techniques use a chemical-etching method to oxidize the metal catalyst, which is heavily time-consuming and involves a high material cost. In this study, a highly efficient symmetrical bi-electrode technique has been developed to simultaneously delaminate the CVD-grown graphene from the metal catalyst at both the anode and cathode of the electrolytic cell. Raman spectra, UV-visible transmittance, and four-probe measurements confirm that this transfer process is nondestructive and can produce similar electrical properties to those produced by the conventional metal-etching transfer method. This bi-electrode transfer technique possesses the advantages of high efficiency, recyclable use of metal catalyst, and high electrical conductivity, and it can be potentially applied for industrial applications.

Batch Fabrication of Flexible Strain Sensors with High Linearity and Low Hysteresis for Health Monitoring and Motion Detection.

In recent years, flexible strain sensors have gradually come into our lives due to their superiority in the field of biomonitoring. However, these sensors still suffer from poor durability, high hysteresis, and difficulty in calibration, resulting in great hindrance of practical application. Herein, starting with interfacial interaction regulation and structure-induced cracking, flexible strain sensors with high performance are successfully fabricated. In this strategy, dopamine treatment is used to enhance the bonding between flexible substrates and carbon nanotubes (CNT). The combination within the conductive networks is then controlled by substituting the CNT type. Braid-like fibers are employed to achieve controllable expansion of the conductive layer cracks. Finally, we obtain strain sensors that possess high linearity (R2 = 0.997) with low hysteresis (5%), high sensitivity (GF = 60) and wide sensing range (0-50%), short response time (62 ms), outstanding stability, and repeatability (>10,000 cycles). Flexible strain sensors with all performances good are rarely reported. Static and dynamic respiration and pulse signal monitoring by the fiber sensor are demonstrated. Moreover, a knee joint monitoring system is constructed for the monitoring of various walking stances, which is of great value to the diagnosis and rehabilitation of many diseases.

Temperature-Triggered Adhesive Bioelectric Electrodes with Long-Term Dynamic Stability and Reusability.

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.

Breathable, Self-Adhesive Dry Electrodes for Stable Electrophysiological Signal Monitoring During Exercise.

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.

Mutually Noninterfering Flexible Pressure-Temperature Dual-Modal Sensors Based on Conductive Metal-Organic Framework for Electronic Skin.

Pressure and temperature are two important indicators for human skin perception. Electronic skin (E-skin) that mimics human skin within one single flexible sensor is beneficial for detecting and differentiating pressure and temperature and showing immunity from tensile strain disruptions. However, few studies have simultaneously realized these conditions. Herein, a flexible and strain-suppressed pressure-temperature dual-modal sensor based on conductive and microstructured metal-organic framework (MOF) films was reported and mainly prepared by in situ growing Ni3(HiTP)2 onto microstructured mixed cellulose (MSMC) substrates. The sensor exhibits distinguishable and strain-suppressed properties for pressure (sensing range up to 300 kPa, sensitivity of 61.61 kPa-1, response time of 20 ms, and ultralow detection limit of 1 Pa) and temperature sensing (sensitivity of 57.1 µV/K). Theoretical calculations successfully analyzed the mutually noninterfering mechanism between pressure and temperature. Owing to its effective perception in static and dynamic surroundings, this sensor has great potential applications, such as in electronic skin and smart prosthetics.

Strain Sensor with Both a Wide Sensing Range and High Sensitivity Based on Braided Graphene Belts.

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.

Through-Layer Buckle Wavelength-Gradient Design for the Coupling of High Sensitivity and Stretchability in a Single Strain Sensor.

Recent years have witnessed a breathtaking development of wearable strain sensors. Coupling high sensitivity and stretchability in a strain sensor is greatly desired by emerging wearable applications but remains a big challenge. To tackle this issue, a through-layer buckle wavelength-gradient design is proposed and a facile and universal fabrication strategy is demonstrated to introduce such a gradient into the sensing film with multilayered sensing units. Following this strategy, strain sensors are fabricated using graphene woven fabrics (GWFs) as sensing units, which exhibit highly tunable electromechanical performances. Specifically, the sensor with 10-layer GWFs has a gauge factor (GF) of 2996 at a maximum strain of 242.74% and an average GF of 327. It also exhibits an extremely low minimum detection limit of 0.02% strain, a fast signal response of less than 90 ms, and a high cyclic durability through more than 10 000 cycling test. Such excellent performances qualify it in accurately monitoring full-range human activities, ranging from subtle stimuli (e.g., pulse, respiration, and voice recognition) to vigorous motions (finger bending, walking, jogging, and jumping). The combination of experimental observations and modeling study shows that the predesigned through-layer buckle wavelength gradient leads to a layer-by-layer crack propagation process, which accounts for the underlying working mechanism. Modeling study shows a great potential for further improvement of sensing performances by adjusting fabrication parameters such as layers of sensing units ( n) and step pre-strain (εsp). For one thing, when εsp is fixed, the maximum sensing strain could be adjusted from >240% ( n = 10) to >450% ( n = 15) and >1200% ( n = 20). For the other, when n is fixed, the maximum sensing strain could be adjusted from >240% (εsp = 13.2%) to >400% (εsp = 18%) and >800% (εsp = 25%).

Copper Nanowire-Based Aerogel with Tunable Pore Structure and Its Application as Flexible Pressure Sensor.

Aerogel is a kind of material with high porosity and low density. However, the research on metal-based aerogel with good conductivity is quite limited, which hinders its usage in electronic devices, such as flexible pressure sensors. In this work, we successfully fabricate copper nanowire (CuNW) based aerogel through a one-pot method, and the dynamics for the assembly of CuNWs into hydrogel is intensively investigated. The "bubble controlled assembly" mechanism is put forward for the first time, according to which tunable pore structures and densities (4.3-7.5 mg cm-3) of the nanowire aerogel is achieved. Subsequently, ultralight flexible pressure sensors with tunable sensitivities (0.02 kPa-1 to 0.7 kPa-1) are fabricated from the Cu NWs aerogels, and the negative correlation behavior of the sensitivity to the density of the aerogel sensors is disclosed systematically. This work provides a versatile strategy for the fabrication of nanowire-based aerogels, which greatly broadens their application potential.

High-Performance Piezoresistive Electronic Skin with Bionic Hierarchical Microstructure and Microcracks.

Electronic skin (E-skin), a popular research topic at present, has achieved significant progress in a variety of sophisticated applications. However, the poor sensitivity and stability severely limit the development of its application. Here, we present a facile, cost-effective, and scalable method for manufacturing E-skin devices with bionic hierarchical microstructure and microcracks. Our devices exhibit high sensitivity (10 kPa-1) and excellent durability (10 000 cycles). The synergistic enhancement mechanism of the hierarchical microstructure and the microcracks on the conductive layers was discovered. Moreover, we carried out a series of studies on the airflow detection and the noncontact speech recognition.

Room-Temperature Surface Modification of Cu Nanowires and Their Applications in Transparent Electrodes, SERS-Based Sensors, and Organic Solar Cells.

Cu nanowires (Copper nanowires) have attracted lots of attention recently due to their potential applications in transparent electrodes, surface enhanced Raman scattering (SERS) based sensors, and solar cells. However, as the surface composition and morphology of Cu nanowires severely influence the performance of the devices based on them, facile surface modification methods need to be developed. Herein, we propose a room-temperature, time-saving aqueous solution method, through which clean Cu nanowires with small Ag nanoparticles decorating around them could be achieved. The unique "sesame candy bar" structure of Cu nanowires brought about significant enhancement on the electrical, optical, and mechanical performances of Cu nanowire networks. Transparent electrodes with ideal opto-electrical performance (47 Ω sq-1 @ 89.1% T) and high antioxidation, antithermal, and electrical stability were fabricated. Stretchable electrodes based on the modified Cu nanowire networks showed superior stretch-ability and cyclic stability. SERS sensors and organic solar cells based on Cu nanowire networks exhibited high performance due to the enhanced surface plasmonic coupling and light scattering effect. We believe that the method will shed light on the large-scale fabrication and application of Cu nanowire based devices.

[Pre- and post-iodine nutritional status among the population related to the practice of new standard on edible iodized salt, in Yunnan province].

OBJECTIVE: In order to understand the iodine nutritional status, after the salt-iodine content was showed a reduction in 2012 and to evaluate the current situation after the new standards was brought into force to the general population in an experimental community of Yunnan province. METHODS: Randomly sampled urine and salt were collected, to test the iodine concentration in the study-site. Pre-and post-levels of the iodized salt under the provision of the new standards, were identified. RESULTS: of this study were gathered upon 3 weeks or 3 months, respectively. Results Data from the three randomly chosen study sites showed that the urine iodine concentration in the general populations was reducing gradually. In the general population, medians of Urine Iodine (MUI) were 279.71 µg/L, 239.64 µg/L and 226.26 µg/L, respectively. Proportion of the urine iodine value for 100-199 µg/L increased but ≥300 µg/L decreased, after the new standard was put into practice. Both homogeneity and stability of the new standard on iodized salt seemed to be good. CONCLUSION: Iodine nutrition in general population appeared reasonable under the use of newly set salt-iodine standards in general population living in Yunnan province.

Micellar-enhanced ultrafiltration of cadmium and methylene blue in synthetic wastewater using SDS.

Single and simultaneous removal of Cd(2+) and methylene blue (MB) with sodium dodecyl sulfate (SDS) by micellar-enhanced ultrafiltration under different experimental conditions was investigated. In single removal process, with initial SDS concentration increasing, the removal efficiency of Cd(2+) and MB kept increasing and then decreased. When the initial concentrations of SDS and Cd(2+) were 1.0 cmc and 50 mg L(-1), respectively, the maximum removal efficiency of Cd(2+) was obtained as 99.2%. Removal efficiency of MB could achieve more than 99.9% with initial SDS concentration below 2.0 cmc. As compared with single Cd(2+) removal, the removal efficiency of Cd(2+) in the presence of MB was slightly higher with initial SDS concentration below 1.0 cmc, while decreased with the SDS concentration above 1.0 cmc. The maximum removal efficiency of Cd(2+) was 98.8% when initial concentrations of SDS and MB were 1.0 cmc and 4 mg L(-1), respectively. The removal efficiency of MB in the presence of Cd(2+) could achieve higher than 96.5%, which was only 3.4% less than the optimum result of the single removal. Meanwhile, effect of pH on removal efficiency of Cd(2+) was more significant than that of MB.

Adsorption of surfactant micelles and Cd2+/Zn2+ in micellar-enhanced ultrafiltration.

Micellar-enhanced ultrafiltration (MEUF) is a powerful treatment developed to remove heavy metals from wastewater. Efficient removal of Cd(2+)/Zn(2+) from wastewater was performed by MEUF using a polysulfone hollow ultrafiltration membrane, with sodium dodecyl sulfate (SDS) as the surfactant. The adsorption of surfactant micelles and Cd(2+)/Zn(2+) in MEUF was studied by changing the surfactant dosage and the Cd(2+)/Zn(2+) concentration in the feed. In addition, kinetics, adsorption isotherms, and thermodynamic rules were analyzed, and X-ray photoelectron spectroscopy (XPS) was conducted. It was found that when the Cd(2+)/Zn(2+) feed concentration was 50 mg/L, and the SDS dosage reached 2.15 g/L, the concentration of heavy metal ions in the permeate stabilized at around 1-4 mg/L, and the adsorption of Cd(2+)/Zn(2+) on SDS micelles followed second-order kinetics and the Langmuir isotherm laws. Adsorption is a spontaneous endothermic process in which the adsorption force is principally the attraction of opposite electrical charges.