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•Highly stretchable and conductive PADL organohydrogels were fabricated.•They exhibited good mechanical properties and strong adhesiveness.•Antibacterial, anti-freezing and ...self-healing performances were achieved.•The strain sensors exhibited relatively high sensitivity (GF = 7.91).
The development of wearable devices promotes the multi-functional applications of conductive materials. Herein, highly stretchable PADL organohydrogels which consist of lignosulfonate nanoparticles (nano-LGS) doped poly(acrylic acid-co-2-(methacryloyloxy)ethyl trimethyl ammonium chloride) in Glycerol/H2O were prepared by a facile strategy. The organohydrogels exhibited strong adhesiveness, high self-healing ability and conductivity. Benefiting from the use of Glycerol/H2O binary solvent system, the fabricated organohydrogels showed anti-freezing property at −40 °C. Notably, nano-LGS acted as the enhancement particles to improve the mechanical properties, antibacterial activity as well as conductivity of PADL organohydrogels. Furthermore, strain sensors constructed by the organohydrogels can monitor human movements with high sensitivity (gauge factor of 7.91). Besides, they can detect handwriting as well. Thus, this work could provide a promising strategy for the fabrication of the self-healing and conductive organohydrogels in the application of wearable electronic devices.
Developing flexible, stretchable, and self-healing wearable electronic devices with skin-like capabilities is highly desirable for healthcare and human-machine interaction. Hydrogels as a promising ...sensing material with crosslinked polymer networks have received widespread attention for decades. However, sensors based on hydrogels suffer from low sensitivity and stability due to their poor electrical conductivity or the movement of nanofillers in hydrogel networks. Herein, a stable, sensitive, and self-healing strain sensor is fabricated by the Ti3C2Tx MXene nanosheets/polyvinyl alcohol (PVA) hydrogel (T-hydrogel). The introduction of MXene increases the number of H-bonds in the PVA hydrogel network and enhances the conductivity, resulting in high sensitivity, stability, and self-healing character. The self-healing T-hydrogel-based strain sensor has a performance close to that of the original sensor. In addition, the device is capable of detecting bodily motions, indicating the potential application in the field of human health monitoring and human-computer interaction.
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•A stable and sensitive strain sensor based on Ti3C2Tx MXene nanosheets/polyvinyl alcohol (PVA) hydrogel (T-hydrogel).•The device possessed autonomous electro-mechanical self-healing abilities in the ambient.•The strain sensor shows potential applications in bodily motion monitoring.
Developing superelastic and superhydrophilic carbon aerogels with intriguing mechanical properties is urgently desired for achieving promising performances in highly compressive supercapacitors and ...strain sensors. Herein, based on synergistic hydrogen bonding, electrostatic interaction, and π–π interaction within regularly arranged layered porous structures, conductive carbon aerogels with cellulose nanofibrils (CNF), carbon nanotubes (CNT) and reduced graphene oxide (RGO) are developed via bidirectional freezing and subsequent annealing. Benefiting from the porous architecture and high surface roughness, CNF/CNT/RGO carbon aerogels exhibit ultralow density (2.64 mg cm–3) and superhydrophilicity (water contact angle ≈0° at 106 ms). The honeycomb‐like ordered porous structure can efficiently transfer stress in the entire microstructure, thereby endowing carbon aerogels with high compressibility and extraordinary fatigue resistance (10,000 cycles at 50% strain). These aerogels can be assembled into compressive solid‐state symmetric supercapacitors showing excellent area capacitance (109.4 mF cm–2 at 0.4 mA cm–2) and superior long cycle compression performance (88% after 5000 cycles at compressive strain of 50%). Furthermore, the aerogels reveal good linear sensitivity (S = 5.61 kPa–1) and accurately capture human bio‐signals as strain sensors. It is expected that such CNF/CNT/RGO carbon aerogels will provide a novel multifunctional platform for wearable electronics, electronic skin, and human motion monitoring.
A type of multifunctional, superhydrophilic, and highly compressible ultralight nanocellulose‐based carbon aerogels is realized for achieving promising performances in compressive supercapacitors and strain sensors by bidirectional freezing and subsequent annealing. Such carbon aerogels provide a novel multifunctional platform for wearable electronics, electronic skin, and human motion signal detection.
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•A self-adhesive and anti-freezing organohydrogel was prepared by a copolymerization.•The organohydrogel exhibits extreme temperature tolerance and fatigue resistance.•The ...organohydrogel could be used as a sensor to monitor human motions.
The design of conductive hydrogel materials with cold-adaptive and flexible properties is of great practical significance for preparing flexible wearable electronics to adapt to the application needs of different environments. However, traditional hydrogel-based sensors are often severely affected in terms of operating temperature range, detection accuracy, and long-term stability under extreme environments. In this study, inspired by the freezing resistance and adhesion chemistry of organisms in the nature, an organohydrogel with self-adhesive characteristics and extreme temperature tolerance, consisting of a binary solvent system of water and glycerol, is fabricated. A pyrogallol–borate complex and polypyrrole nanoparticles are incorporated into the polymer networks, which provide excellent adhesion and electrical conductivity to the organohydrogel, respectively. This conductive and shape-adaptable organohydrogel exhibits extraordinary self-adhesion, suitable mechanical strength, and excellent fatigue resistance for meeting personalized application requirements. Meanwhile, it can withstand a low temperature of −80 °C for 24 h without freezing and maintain an excellent electrical conductivity (0.12 S m−1) and high gauge factor (GF = 4.9). Therefore, the organohydrogel-based sensor exhibits excellent antifreeze properties and can be used in personal health and human–machine interfaces for extreme ice and snow sports. More importantly, the sensor can also simulate the standard of real-time capture of the skier’s body movements, providing a reference for judges to score. This study provides an exciting new direction for the development of wearable strain sensing devices.
Robust, stretchable, and strain-sensitive hydrogels have recently attracted immense research interest because of their potential application in wearable strain sensors. The integration of the ...synergistic characteristics of decent mechanical properties, reliable self-healing capability, and high sensing sensitivity for fabricating conductive, elastic, self-healing, and strain-sensitive hydrogels is still a great challenge. Inspired by the mechanically excellent and self-healing biological soft tissues with hierarchical network structures, herein, functional network hydrogels are fabricated by the interconnection between a “soft” homogeneous polymer network and a “hard” dynamic ferric (Fe3+) cross-linked cellulose nanocrystals (CNCs–Fe3+) network. Under stress, the dynamic CNCs–Fe3+ coordination bonds act as sacrificial bonds to efficiently dissipate energy, while the homogeneous polymer network leads to a smooth stress-transfer, which enables the hydrogels to achieve unusual mechanical properties, such as excellent mechanical strength, robust toughness, and stretchability, as well as good self-recovery property. The hydrogels demonstrate autonomously self-healing capability in only 5 min without the need of any stimuli or healing agents, ascribing to the reorganization of CNCs and Fe3+ via ionic coordination. Furthermore, the resulted hydrogels display tunable electromechanical behavior with sensitive, stable, and repeatable variations in resistance upon mechanical deformations. Based on the tunable electromechanical behavior, the hydrogels can act as a wearable strain sensor to monitor finger joint motions, breathing, and even the slight blood pulse. This strategy of building synergistic “soft and hard” structures is successful to integrate the decent mechanical properties, reliable self-healing capability, and high sensing sensitivity together for assembling a high-performance, flexible, and wearable strain sensor.
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•Nanocomposite hydrogels possess high transparency, large stretchability, superb conductivity, good self-adhesiveness and excellent anti-freezing ability were prepared via simple in ...situ free radical polymerization.•Nanocomposite hydrogel-based sensors exhibit high sensitivity and fast responsive time.•Both large and subtle human activities can be detected by hydrogel-based sensors.
Conductive hydrogels have attracted considerable attentions due to their great potential in the field of flexible strain sensors. However, the low stretchability, poor adhesiveness as well as the lack of freezing-resistant capacity of conventional conductive hydrogels greatly limited their practical applications. Herein, a stretchable, transparent, self-adhesive and anti-freezing conductive nanocomposite hydrogel (PAHS gel) was fabricated via a one-step in situ free-radical polymerization of sulfobetaine methacrylate (SBMA), acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) in the presence of alumina nanoparticles (Al2O3 NPs) and lithium chloride (LiCl) as the inorganic cross-linkers and conductive substance, respectively. The obtained PAHS gels displayed high transparency (higher than 85 % at 550 nm), excellent stretchability (up to 800 %) and good ionic conductivity (2.25 S/m) and could keep flexible and conductive at the temperature at −18 ℃. Furthermore, the various types of functional groups on the polymer chains endow the PAHS gels with strong self-adhesiveness to different substrates such as glass, rubber, skin, etc. In addition, the PAHS gels also revealed superior strain sensitivity (GF = 2.69) in the strain of 0 ∼ 100 %, which can be assembled into wearable strain sensors to monitor various human activity. Based on these combined merits, it is believed that this newly developed conductive nanocomposite hydrogel would have prospective applications in the field of wearable strain sensors and other flexible electronics.
Strain sensors with ultrahigh sensitivity under microstrain have numerous potential applications in heartbeat monitoring, pulsebeat detection, sound signal acquisition, and recognition. In this work, ...a two-part strain sensor (i.e., polyurethane part and brittle conductive hybrid particles layer on top) based on silver nanowires/graphene hybrid particles is developed via a simple coprecipitation, reduction, vacuum filtration, and casting process. Because of the nonuniform interface, weak interfacial bonding, and the hybrid particles’ point-to-point conductive networks, the crack and overlap morphologies are successfully formed on the strain sensor after a prestretching; the crack-based stain sensor exhibits gauge factors as high as 20 (Δε < 0.3%), 1000 (0.3% < Δε < 0.5%), and 4000 (0.8% < Δε < 1%). In addition, we demonstrate the sensing mechanism under strain results in the high gauge factor of the strain sensor. Combined with its good response to bending, high strain resolution, and high working stability, the developed strain sensor is promising in the applications of electronic skins, motion sensors, and health monitoring sensors.
Conductive hydrogels can be prepared by incorporating various conductive materials into polymeric network hydrogels. In recent years, conductive hydrogels have been developed and applied in the field ...of strain sensors owing to their unique properties, such as electrical conductivity, mechanical properties, self‐healing, and anti‐freezing properties. These remarkable properties allow conductive hydrogel‐based strain sensors to show excellent performance for identifying external stimuli and detecting human body movement, even at subzero temperatures. This review summarizes the properties of conductive hydrogels and their application in the fabrication of strain sensors working in different modes. Finally, a brief prospectus for the development of conductive hydrogels in the future is provided.
Conductive hydrogels are extensively studied in the field of strain sensors due to their conductivity, mechanical properties, self‐healing, and anti‐freezing properties, which allow strain sensors to show excellent performance even at subzero temperatures. This review summarizes the properties of conductive hydrogels and their application in the fabrication of strain sensors working in different modes.
Flexible energy storage devices play a pivotal role in realizing the full potential of flexible electronics. This work presents high‐performance, all‐solid‐state, flexible supercapacitors by ...employing an innovative multilevel porous graphite foam (MPG). MPGs exhibit superior properties, such as large specific surface area, high electric conductivity, low mass density, high loading efficiency of pseudocapacitive materials, and controlled corrugations for accommodating mechanical strains. When loaded with pseudocapacitive manganese oxide (Mn3O4), the MPG/Mn3O4 (MPGM) composites achieve a specific capacitance of 538 F g−1 (1 mV s−1) and 260 F g−1 (1 mV s−1) based on the mass of pure Mn3O4 and entire electrode composite, respectively. Both are among the best of Mn3O4‐based supercapacitors. The MPGM is mechanically robust and can go through 1000 mechanical bending cycles with only 1.5% change in electric resistance. When integrated as all‐solid‐state symmetric supercapacitors, they offer a full cell specific capacitance as high as 53 F g−1 based on the entire electrode and retain 80% of capacitance after 1000 continuous mechanical bending cycles. Furthermore, the all‐solid‐state flexible supercapacitors are incorporated with strain sensors into self‐powered flexible devices for detection of both coarse and fine motions on human skins, i.e., those from finger bending and heart beating.
Ultralight, hierarchically porous graphite foams are employed as electrode supports of all‐solid‐state flexible supercapacitors. The devices exhibit 53 F g−1 full‐cell capacitance based on the entire weight of electrodes and 80% capacitance retention after 1000 bending cycles. Moreover, they seamlessly integrate with wearable strain sensors for self‐powered detection of both coarse and fine motions, e.g., those from finger bending and heart pulses.
A flexible and multi-functional sensor based on all-carbon sensing medium for ultrahigh-performance strain, temperature and humidity sensing has been investigated via an easy and low-cost method. The ...sensor can detect different external stimuli simultaneously with high sensitivity, broad detection range, fast response, high signal–to-noise ratio and low coupling, indicating great potential in multi-functional sensing devices.
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An ultrahigh-performance multi-functional sensor integrating strain, temperature and humidity sensing has been investigated. The sensing medium is only composed of carbon nanocoils (CNCs) and carbon nanotubes (CNTs). For strain sensing, due to the high elasticity provided by CNC skeleton and the recoverable conductive cracks with a width of hundreds of microns generated by the dense CNT film, the sensor delivers excellent sensing properties, including the advantages of ultrahigh gauge factor (up to 352085), wide strain range (up to 100%), high strain resolution (0.01%), fast response time (16 ms) and robust cycle stability (10000 cycles). In addition, this all–carbon sensing medium can also be used for temperature and humidity sensing in an ultrawide temperature range of 7 to 400 K and humidity sensing over a relative humidity range of 10% to 80% with a high signal-to-noise ratios. It is worth noting that the integrated multi-functional sensor can simultaneously detect the stimuli of strain, temperature and humidity with low coupling. Multiple applications can be detected accurately, such as human motions, breathing behavior, pulse wave, different vibration modes and so on. Therefore, the all-carbon-based sensor provides a promising strategy in developing multi-functional integration for smart wearable devices, electronic skins, and other multi-functional sensing devices.
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