Serpentine-Inspired Strain Sensor with Predictable Cracks for Remote Bio-Mechanical Signal Monitoring.

Flexible strain sensors have attracted intense interest due to their application as intelligent wearable electronic devices. However, it is still a huge challenge to achieve a flexible sensor with simultaneous high sensitivity, excellent durability, and a wide sensing region. In this work, a crack-based strain sensor with a paired-serpentine conductive network is fabricated onto flexible film by screen printing. The innovative conductive network exhibits a controlled crack morphology during stretching, which endows the prepared sensor with outstanding sensing characteristics, including high sensitivity (gauge factor up to 2391.5), wide detection (rang up to 132%), low strain detection limit, a fast response time (about 40 ms), as well as excellent durability (more than 2000 stretching/releasing cycles). Benefiting from these excellent performances, full-range human body motions including subtle physiological signals and large motions are accurately detected by the prepared sensor. Furthermore, wearable electronic equipment integrated with a wireless transmitter and the prepared strain sensor shows great potential for remote motion monitoring and intelligent mobile diagnosis for humans. This work provides an effective strategy for the fabrication of novel strain sensors with highly comprehensive performance.

Reinforced macromolecular micelle-crosslinked hyaluronate gels induced by water/DMSO binary solvent.

Introducing macromolecular micelles into a biocompatible hyaluronic acid (HA) hydrogel is a promising strategy to improve its mechanical properties for biomedical applications. However, it is still unclear whether the solvent nature has an influence on the structure and property of HA gels especially when they are used for those cases containing binary solvents because reversible hydrophobic association within micelles could be weakened or even dissociated by organic solvents. In this work, we demonstrated that a binary solvent consisting of water and low-toxic dimethyl sulfoxide (DMSO), a commonly used cryoprotectant agent in biomedicine, can enhance the mechanical properties of hydrophobic-associated methacrylated hyaluronate (MeHA) gels crosslinked by diacrylated PEO99-PPO65-PEO99 (F127DA) macromolecular micelles, namely FH gels. The resulting FH hydro/organo-gels showed a crystalline structure due to polymer/solvent interactions. The FH gels showed a low swelling degree and the maximum strength (10.12 MPa), modulus (106.8 kPa) and toughness (1540 J m-2) in DMSO with a volume fraction of around 0.6. Moreover, the FH gels displayed a rapid recoverability under cyclic loading-unloading stress particularly in the presence of DMSO within the network due to their dual-dynamic dissipation networks. Such novel hydrophobic associated polysaccharide gels with tunable mechanical properties in binary solvents would be attractive in a cryopreservation system for cell-based applications.

Electromagnetic interference shielding of segregated polymer composite with an ultralow loading of in situ thermally reduced graphene oxide.

An in situ thermally reduced graphene/polyethylene conductive composite with a segregated structure was fabricated, which achieved a high electromagnetic interference shielding effectiveness of up to 28.3-32.4 dB at an ultralow graphene loading of 0.660 vol.%. Our work suggests a new way of effectively using graphene.

MnO2 porous carbon composite from cellulose enabling high gravimetric/volumetric performance for supercapacitor.

Preparing electrode material integrated with high gravimetric/volumetric capacitance and fast electron/ion transfer is crucial for the practical application. Owing to the structural contradiction, it is a big challenge to construct electrode material with high packing density, sufficient ion transport channels, and fast electronic transfer pathways. Herein, MnO2 porous carbon composite with abundant porous structure and 3D carbon skeleton was facilely fabricated from Linum usitatissimum. L stems via NaOH activation and MnO2 introduction. The in-situ introduced MnO2 not only increases the packing density and the electrical conductivity of the porous carbon but also provides more active sites for oxidation reactions. These unique characteristics endow the resultant MnO2 porous carbon composite with remarkable gravimetric capacitance of 549 F g-1, volumetric capacitance of 378 F cm-3, and capacitance retention of 54.9 %. Giving the simple process and low cost, this work might offer a new approach for structural design and the practical application of high-performance electrode materials.

Porous nickel-cobalt phosphate with oxygen-rich vacancies in situ grown on dopamine-modified cellulose textiles as self-supporting high mass loadings supercapacitor electrode.

Transition-metal phosphates/phosphides showcase significant promise for energy-related applications because of their high theoretical electrochemical characteristics. However, sluggish electro/ion transfer rates and kinetically unfavorable reaction sites hinder their application at high mass loading. Herein, a self-supporting electrode based on transition-metal phosphates was successfully fabricated via a one-step electrodeposition process. The nanosheet structure of transition-metal phosphates, formed by interconnecting nanoparticles, effectively mitigates the impact of stress and achieves a high mass-loading (21 mg cm-2) of the electrode. Additionally, the oxygen vacancy-rich and porous nanostructure of transition-metal phosphates endows the as-prepared electrodes with a significantly increased conductivity and fast ion migration rate for enhancing electrochemical kinetics. Consequently, the as-fabricated transition-metal phosphate electrode displays the highest areal specific capacity of 39.2F cm-2. Furthermore, the asymmetric supercapacitor achieves a maximum energy density of 0.79 mWh cm-2 and a high capacity retention of 93.0 % for 10000 cycles under 60 mA cm-2. This work provides an ideal strategy for fabricating flexible electrodes with high mass loading and synthesizing transition-metal phosphate electrodes rich in oxygen vacancies.

High-strength, anti-fatigue, cellulose nanofiber reinforced polyvinyl alcohol based ionic conductive hydrogels for flexible strain/pressure sensors and triboelectric nanogenerators.

Ionic conductive hydrogels (ICHs) have attracted great attention because of their excellent biocompatibility and structural similarity with biological tissues. However, it is still a huge challenge to prepare a high strength, conductivity and durability hydrogel-based flexible sensor with dual network structure through a simple and environmentally friendly method. In this work, a simple one-pot cycle freezing thawing method was proposed to prepare ICHs by dissolving polyvinyl alcohol (PVA) and ferric chloride (FeCl3) in cellulose nanofiber (CNF) aqueous dispersion. A dual cross-linked network was established in hydrogel through the hydrogen bonds and coordination bonds among PVA, CNF, and FeCl3. This structure endows the as-prepared hydrogel with high sensitivity (pressure sensitivity coefficient (S) = 5.326 in the pressure range of 0-5 kPa), wide response range (4511 kPa), excellent durability (over 3000 cycles), short response time (83 ms) and recovery time (117 ms), which can accurately detect various human activities in real time. Furthermore, the triboelectric nano-generator (TENG) made from PVA@CNF-FeCl3 hydrogel can not only supply power for commercial capacitors and LED lamps, but also be used as a self-powered sensor to detect human motion. This work provides a new approach for the development of the next generation of flexible wearable electronic devices.

MOF-Derived Co/C and MXene co-Decorated Cellulose-Derived Hybrid Carbon Aerogel with a Multi-Interface Architecture toward Absorption-Dominated Ultra-Efficient Electromagnetic Interference Shielding.

Exploring electromagnetic interference (EMI) shielding materials with ultra-efficient EMI shielding effectiveness (SE) and an absorption-dominated mechanism is urgently required for fundamentally tackling EMI radiation pollution. Herein, zeolitic imidazolate framework-67 (ZIF-67)/MXene/cellulose aerogels were first prepared via a simple solution mixing-regeneration and freeze-drying process. Subsequently, they are converted into electric/magnetic hybrid carbon aerogels (Co/C/MXene/cellulose-derived carbon aerogels) through a facile pyrolysis strategy. ZIF-67-derived porous Co/C could provide the additional magnetic loss capacity. The resultant electric/magnetic hybrid carbon aerogels exhibit a hierarchically porous structure, complementary electromagnetic waves (EMWs) loss mechanisms, and abundant heterointerfaces. The construction of a porous architecture and the synergy of electric/magnetic loss could greatly alleviate the impedance mismatching at the air-specimen interface, which enables more EMWs to enter into the materials for consumption. Moreover, numerous heterointerfaces among Co/C, Ti3C2Tx MXene, and cellulose-derived carbon skeleton induce the generation of multiple polarization losses containing interfacial and dipole polarization, which further dissipate the EMWs. The resultant electric/magnetic hybrid carbon aerogel with a low density (85.6 mg/cm3) achieves an ultrahigh EMI SE of 86.7 dB and a superior absorption coefficient of 0.72 simultaneously. This work not only offers a novel approach to design high-performance EMI shielding materials entailing low reflection characteristic but also broadens the applicability of electric/magnetic hybrid carbon aerogels in aerospace, precision electronic devices, and military stealth instruments.

Effect of Nano-Silica and Sorbitol on the Properties of Chitosan-Based Composite Films.

Chitosan and its derivatives are widely used in food packaging, pharmaceutical, biotechnology, medical, textile, paper, agriculture, and environmental industries. However, the flexibility of chitosan films is extremely poor, which limits its relevant applications to a large extent. In this paper, chitosan/sorbitol/nano-silica (CS/sorbitol/SiO2) composite films were prepared by the casting film method using chitosan, sorbitol, Tween-80 and nano-SiO2 as raw materials. The structure of the films was characterized by infrared spectroscopy, electron scanning microscopy, and X-ray diffraction analysis. The effects of sorbitol and nano-silica dosage on the mechanical properties, thermal properties and water vapor barrier properties of the composite film were investigated. The results show that with the gradual increase in sorbitol (≤75 wt %), the elongation at the break of chitosan/sorbitol films significantly increased. When the addition of sorbitol was 75 wt %, the elongation at break of the chitosan/sorbitol composite film was 13 times higher than that of the chitosan film. Moreover, nano-SiO2 can further improve the mechanical properties and thermal stability of the chitosan/sorbitol composite films. When the amount of nano-silica was 4.5 wt %, the composite film became more flexible, with a maximum elongation of 90.8% (which is 14 times that of chitosan film), and its toughness increased to 10.52 MJm-3 (which is 6 times that of chitosan film). This study balances the tensile strength and elongation at break of the composite films by adding a plasticizer and nano-filler, providing a reference for the preparation of chitosan composites or their blending with other polymers, and has practical guiding significance for the industrial production of biomass plastics.

Spent Coffee Grounds Derived Carbon Loading C, N Doped TiO2 for Photocatalytic Degradation of Organic Dyes.

Titanium dioxide (TiO2) is an ideal photocatalyst candidate due to its high activity, low toxicity and cost, and high chemical stability. However, its practical application in photocatalysis is seriously hindered by the wide band gap energy of TiO2 and the prone recombination of electron-hole pairs. In this study, C, N doped TiO2 were supported on spent coffee grounds-derived carbon (ACG) via in situ formation, which was denoted as C, N-TiO2@ACG. The obtained C, N-TiO2@ACG exhibits increased light absorption efficiency with the band gap energy decreasing from 3.31 eV of TiO2 to 2.34 eV, a higher specific surface area of 145.8 m2/g, and reduced recombination rates attributed to the synergistic effect of a spent coffee grounds-derived carbon substrate and C, N doping. Consequently, the optimal 1:1 C, N-TiO2@ACG delivers considerable photocatalytic activity with degradation efficiencies for methylene blue (MB) reaching 96.9% within 45 min, as well as a high reaction rate of 0.06348 min-1, approximately 4.66 times that of TiO2 (0.01361 min-1). Furthermore, it also demonstrated greatly enhanced photocatalytic efficiency towards methyl orange (MO) in the presence of MB compared with a single MO solution. This work provides a feasible and universal strategy of synchronous introducing nonmetal doping and biomass-derived carbon substrates to promote the photocatalytic performance of TiO2 for the degradation of organic dyes.

Magnetic coupling N self-doped porous carbon derived from biomass with broad absorption bandwidth and high-efficiency microwave absorption.

Nowadays, developing microwave absorption materials (MAMs) with thin thickness, wide-frequency effective absorption bandwidth (EAB) and strong absorbing capacity is an urgent requirement to tackle the increasingly serious electromagnetic radiation issue. Herein, we report a novel high-performance MAMs by growing Fe3O4 nanoparticles on activated porous carbon derived from egg white via a facile carbonization and subsequent hydrothermal approach. The resultant composite features three-dimensional hierarchical porous carbon embedded with Fe3O4 nanoparticles. Benefiting from the balanced impedance matching and the multi-loss that involve the conductive loss, dielectric loss, dipolar/interfacial polarization loss and magnetic loss, the prepared composite achieves a minimum reflection loss (RL) of -43.7 dB at 9.92 GHz and a broad EAB (RL < -10 dB) of 7.52 GHz (6.24-13.76 GHz) at a thin thickness of 2.5 mm and a low filler content of 20 wt%. This work provides new insights for exploring novel magnetic coupling porous carbon derived from biomass with high-efficiency microwave absorption performance.

Three-dimensional macroporous hybrid carbon aerogel with heterogeneous structure derived from MXene/cellulose aerogel for absorption-dominant electromagnetic interference shielding and excellent thermal insulation performance.

The development of electromagnetic interference (EMI) shielding materials with excellent absorption coefficient (A) is vital to completely eliminate the pollution of the ever-increasing electromagnetic waves (EMWs). In this regard, a TiC/carbon hybrid aerogel, derived from MXene/cellulose aerogel, was successfully fabricated via freeze-drying and subsequent pyrolysis process. Profiting from the open, loose three-dimensional (3D) macro pores with sheet-like morphology and high porosity, as well as the rich heterogeneous interfaces between TiC and cellulose-derived carbon, the as-prepared hybrid carbon aerogel achieves ultra-efficient EMI shielding effectiveness of 72.9 dB in conjunction with a superior A value of 0.76 and low thermal conductivity. These properties endow the as-prepared aerogel with strong absorption-dominant ultra-efficient EMI shielding and thermal insulation performance to meet the complex practical requirements. This work provides a promising strategy for achieving ultra-efficient multifunctional EMI shielding performance and superior A simultaneously.

Multifunctional CoFe2O4@MXene-AgNWs/Cellulose Nanofiber Composite Films with Asymmetric Layered Architecture for High-Efficiency Electromagnetic Interference Shielding and Remarkable Thermal Management Capability.

Developing high-efficiency electromagnetic interference (EMI) shielding composite films with outstanding flexibility and excellent thermal management capability is vital but challenging for modern integrated electronic devices. Herein, a facile two-step vacuum filtration method was used to fabricate ultrathin, flexible, and multifunctional cellulose nanofiber (CNF)-based composite films with an asymmetric layered architecture. The asymmetric layered structure is composed of a low-conductivity CoFe2O4@MXene/CNF layer and a highly conductive silver nanowires (AgNWs)/CNF layer. Benefiting from the rational placement of the impedance matching layer and shielding layer, as well as the synergistic effect of electric and magnetic losses, the resultant composite film exhibits an extremely high EMI shielding effectiveness (SE) of 73.3 dB and an average EMI SE of 70.9 dB with low reflected efficiency of 4.9 dB at only 0.1 mm thickness. Sufficiently reliable EMI SE (over 95% reservation) is attained even after suffering from continuous physical deformations and long-term chemical attacks. Moreover, the prepared films exhibit extraordinary flexibility, strong mechanical properties, and satisfactory thermal management capability. This work offers a viable strategy for exploiting high performance EMI shielding films with attractive thermal management capacity, and the resultant films present extensive application potential in aerospace, artificial intelligence, advanced electronics, stealth technology, and the national defense industry, even under harsh environments.

Facile construction of core-shell Carbon@CoNiO2 derived from yeast for broadband and high-efficiency microwave absorption.

Manufacturing dielectric/magnetic composites with hierarchical structure is regard as a promising strategy for the progress of high-performance microwave absorption (MA) materials. In this paper, the nano-grass structured CoNiO2 magnetic shell was uniformly anchored on the yeast-derived carbon microspheres by in-situ one-pot synthesis method. Profiting from the unique nano-grass and core-shell structure, capable dielectric/magnetic loss, along with improved impedance matching, the prepared absorber realizes desirable MA performance. The minimum reflection loss (RLmin) reaches up to -44.06 dB at 6.56 GHz. Moreover, the effective absorption bandwidth (EAB, reflection loss (RL) < -10 dB) accomplishes 7.04 GHz under a low filler loading of 20 wt%. This work endeavors a valuable insight for designing innovative core-shell structured materials with high-efficiency MA and broad bandwidth.

Temperature dependence of graphene oxide reduced by hydrazine hydrate.

Graphene oxide (GO) was successfully prepared by a modified Hummer's method. The reduction effect and mechanism of the as-prepared GO reduced with hydrazine hydrate at different temperatures and time were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), x-ray diffractions (XRD), Raman spectroscopy and thermo-gravimetric analysis (TGA). The results showed that the reduction effect of GO mainly depended on treatment temperature instead of treatment time. Desirable reduction of GO can only be obtained at high treatment temperature. Reduced at 95 °C for 3 h, the C/O atomic ratio of GO increased from 3.1 to 15.1, which was impossible to obtain at low temperatures, such as 80, 60 or 15 °C, even for longer reduction time. XPS, 13C NMR and FTIR results show that most of the epoxide groups bonded to graphite during the oxidation were removed from GO and form the sp(2) structure after being reduced by hydrazine hydrate at high temperature (>60 °C), leading to the electric conductivity of GO increasing from 1.5 × 10(-6) to 5 S cm(-1), while the hydroxyls on the surface of GO were not removed by hydrazine hydrate even at high temperature. Additionally, the FTIR, XRD and Raman spectrum indicate that the GO reduced by hydrazine hydrate can not be entirely restored to the pristine graphite structures. XPS and FTIR data also suggest that carbonyl and carboxyl groups can be reduced by hydrazine hydrate and possibly form hydrazone, but not a C = C structure.

Flexible and Anisotropic Strain Sensors with the Asymmetrical Cross-Conducting Network for Versatile Bio-Mechanical Signal Recognition.

Flexible strain sensors with high performance are actively and widely investigated for wearable electronic devices. However, the conventional sensors often suffer from a lack of detection of complex multidimensional strain, which severely limits their wide applications. To overcome this critical challenge, we propose a pattern design by screen printing to construct an asymmetrical cross-conductive network in the piezoresistive strain sensor, which can enhance the response to external stimuli in different directions. The unique network endows the prepared sensors with the excellent ability of instantaneous detection and accurate identification of multidimensional strains. Moreover, the sensor also demonstrates high sensitivity, fast response, an ultra-wide sensing range, and excellent stability and durability. Benefiting from the outstanding comprehensive performance of the prepared sensor, a full range of human actions (wink, smile, swallowing, and joint bending) and subtle bio-signals (pulse and breathing) are easily and accurately monitored. A wireless wearable device assembled by the sensor shows great potential applications in practical real-time physiological monitoring and intelligent mobile diagnosis for humans. This work provides an innovative and effective strategy for manufacturing flexible and multifunctional strain sensors to fully satisfy versatile applications of new-generation wearable electronic devices.

Facile synthesis of chitosan-based acid-resistant composite films for efficient selective adsorption properties towards anionic dyes.

To effectively and selectively remove toxic anionic dyes which are heavily discharged and to promote them recovery, a sustainable cellulose nanofiber/chitosan (CNF/CS) composite film was elaborately designed through a facile procedure. Based on the strong supporting effect of CNF and excellent compatibility between CNF and CS, the composite film presents low swelling and acid-proof properties, which can prevent the adsorption process from the disintegration of adsorbent. Moreover, the positive electrical property of CNF/CS film increases the discrepancy in adsorption capacities for anionic and cationic dyes. The maximum adsorption capacity of anionic methyl orange (MO) on CNF/CS film reaches 655.23 mg/g with a desirable recyclability. The adsorption behavior attributed to a physico-chemical and monolayer adsorption process. This work opens a new route for the development of eco-friendly and highly efficient adsorbents on selective removal and recycling of anionic dyes from wastewater.

Biomimetic epidermal sensors assembled from polydopamine-modified reduced graphene oxide/polyvinyl alcohol hydrogels for the real-time monitoring of human motions.

Conductive hydrogel-based epidermal strain sensors can generate repeatable electrical changes upon mechanical deformations for indication of the skin's physiological condition. However, this remains challenging for many conductive hydrogel sensors due to biomechanical mismatch with skin tissues and an unstable resistance variation response, resulting in non-conformable deformations with the epidermis and dermis, and consequently generating inaccurate monitoring of human movements. Herein, a conductive hydrogel that highly matches the skin is fabricated from dynamically hydrogen-bonded nanocrystallites of polydopamine-modified reduced graphene oxide (PDA-rGO) nanosheets composited with polyvinyl alcohol, namely the PDA-rGO/PVA hydrogel. PDA-rGO provides a large number of dynamic hydrogen-bonding interactions in the hydrogel, resulting in a skin-matching modulus (78 kPa) and stretchability. Moreover, the resultant hydrogel possesses excellent cytocompatibility and conductivity (0.87 S m-1), high sensitivity (gauge factor of compression: 20) at low strain and outstanding linearity at high strain as well as a stable resistance variation response. These desirable properties enable the application of the PDA-rGO/PVA hydrogel as a skin-friendly wearable sensor for real-time and accurate detection of both large-scale joint movements and tiny physiological signals, including the bending and relaxing of fingers, the wrist, elbow and knee joints, and wrist pulse and swallowing. Moreover, this hydrogel is integrated into a 2D sensor array that monitors strains or pressures in two dimensions, which is promising for electronic skin, biosensors, human-machine interfaces, and wearable electronic devices.

The Dependence of Acoustic Emission Performance on the Crystal Structures, Dielectric, Ferroelectric, and Piezoelectric Properties of the P(VDF-TrFE) Sensors.

To clarify the influence of various molar concentrations of vinylidene fluoride (VDF) on the piezoelectric and acoustic emission (AE) reception performances of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] sensors, we systematically investigated the crystal structures and the dielectric and ferroelectric properties of P(VDF-TrFE) films with different compositions of VDF and TrFE monomers and found that low proportion (<30 mol%) TrFE as a wedge inserted into molecular chains of P(VDF-TrFE) will not only improve the fraction of regular ß -phase crystal grains but also decrease the dielectric constant ( εr ) of these copolymers, which favors the piezoelectric voltage coefficient ( g33 ) of this P(VDF-TrFE) film. As such, a considerable remanent electric polarization ( [Formula: see text]/cm2) under 200 MV/m and a large piezoelectric coefficient ( d 33  âˆ¼ -25 pC/N) are obtained in P(VDF-TrFE) 80/20-mol% films. It is worth noting that a sensor made from P(VDF-TrFE) 80/20 mol% shows an attractive AE reception property of approximately 84 dB, a high signal voltage of above 10 mV from time-domain analysis, and a large signal voltage of above 4 mV from frequency-domain analysis, which are close to standard lead zirconate titanate (PZT) sensors. Considering its unique characters of flexibility, no required stretching, easily shaped, having high thermal Faille temperatures ( [Formula: see text]), etc., P(VDF-TrFE) piezoelectric film is considered a promising material for sensors, actuators, and energy transfer units.

Facile synthesis of trimethylammonium grafted cellulose foams with high capacity for selective adsorption of anionic dyes from water.

The increasing amount of dye discharge is imposing more stringent requirements on dye removal than ever before. In this work, a three-dimensional network structured cationic cellulose foam (CCF) with high dye adsorption capability and highly selective adsorption of anionic dyes is prepared through grafting and chemical crosslinking. It exhibits a maximum anionic dye Eosin Y (EY) adsorption capacity of 364.22 mg/g and a corresponding removal efficiency as high as 99.58 %. Besides, results indicate that the obtained CCF displays superior adsorption capability for anionic dyes, environmental adaptability, as well as high recyclability. The isothermal and kinetics of the dye adsorption highly match Langmuir and the pseudo-second-order kinetic model, suggesting that anionic dyes are absorbed on CCF through chemical and monolayer action. All these merits demonstrate a simple, feasible and effective approach for the design and fabrication of cellulose foams with selective adsorption of anionic dyes from wastewater.

A Highly Sensitive and Broad-Range Pressure Sensor Based on Polyurethane Mesodome Arrays Embedded with Silver Nanowires.

The pressure sensor with high sensitivity and a broad pressure sensing range is highly desired for flexible electronics. Here, a high-performance pressure sensor based on a hybrid structure was facilely fabricated using the glass template method, which consists of polyurethane (PU) mesodomes embedded with gradient-distributed silver nanowire (AgNW). Such a novel hybrid architecture enables the as-prepared PU/AgNW pressure sensor to have high sensitivity as well as a wide detection range. Moreover, the obtained PU/AgNW pressure sensors have a fast response time (20 ms), good cycling stability, and excellent flexibility. The pressure sensor, benefiting from its outstanding comprehensive sensing performance, can be used for expression recognition and human activity monitoring, showing tremendous application potential in wearable devices. The proposed architecture and developed methodology in this work is promising for future flexible electronic applications.