Wearable sensors are the development trend in the future iteration of medical devices, in which, flexible tem-perature sensors with high resolution, fast response speed, and good reliability under deformations, are one of the much important devices. In this study, a nano multilayer sensing structured fiber temperature sensor is fabricated via in situ coating reduced graphene oxide (rGO) and chitosan (CS) on the surface of stretchable polyurethane fiber (PF) by a layer-by-layer self-assembly method. The introduction of CS not only enhances the temperature sensitivity (with a temperature coefficient of -1.379 %.degrees C-1 in the range of 30-60 degrees C) of the rGO-based fiber sensors but also greatly increases the mechanical stability of the nanofibrous membrane. Most importantly, the fiber-shaped temperature sensor shows a fast response time (2.4 s) and recovery time (3.9 s) to temperature. Moreover, the sensor achieves a high temperature resolution of 0.1 degrees C. Made from a simple and low-cost process, the fiber-like devices can be easily integrated into items such as gloves or face masks to monitor the real-time temperature changes. The results demonstrate the great potential of rGO-based fiber sensors for applications in human healthcare monitoring.

Flexible temperature sensors with superior resolution and reliable repeatability are crucial in the burgeoning field of electronic skins (e-skins). In this study, we synthesized thermo-responsive materials with mechanical flexibility by incorporating multi-wall carbon nanotubes (MWCNT) into waterborne polyurethane (WPU) matrix via covalent bonding. The thermal movement of WPU chain segments serves as the driving force, endowing the resultant material with excellent temperature response properties and stability. The MWCNT@WPU sensor demonstrates ultra-high sensitivity (-5.63 % K-- 1 ), high accuracy (0.1 degrees C), rapid response (mere 4.5 s), and longterm durability (up to 30 days) for temperature sensing within the range of 30 to 60 degrees C. Importantly, the temperature coefficient of resistance (TCR) can be tailored by adjusting the molecular weight of WPU soft segments and the ratio of hard segment to soft segment in WPU. Moreover, the developed sensor exhibits outstanding detection accuracy and stability in practical applications such as continuous water temperature monitoring, breathing rate measurement, and human skin temperature sensing, highlighting its immense potential in the e-skins field, catering to applications in healthcare monitoring, intelligent robotic platforms, and environmental surveillance.

Hydrogel-based wearable electronic devices have received growing interest in recent years. However, swelling of hydrogels in an aquatic environment dramatically diminishes their mechanical and electrical properties, thus hampering the practical applications. The construction of underwater strain sensors is a considerable challenge. In this study, we report a strategy to introduce the metal coordination network into the PVA network and successfully prepare an anti-swelling gel material. The anti-swelling property (equilibrium swelling ratio of 0% after 8 d in water) is achieved by the grafting of poly(Cu-arylacetylide) chains and the introduction of the metal-ligand network. Compared with PVA hydrogel, the tensile strength of the s anti-swelling hydrogel increased from 10 kPa to 139 kPa, the elongation at break increased from 133% to 341%, and the Young's modulus increased from 10 kPa to 18 kPa. Notably, the hydrogel can retain 88% of its initial toughness after 20 d of immersion in an aquatic environment. The anti-swelling hydrogel has good reliability in detecting small and large strains. On this basis, a strain sensor is further developed, which has high sensitivity in monitoring movement in air and underwater. Moreover, hydrogel-based wireless electronic devices are also developed, demonstrating their promise for communication in complex water environments. It is believed that the design of our anti-swelling hydrogel will provide the impetus for expanding the application of wearable electronic devices.

Conductive hydrogels have gained significant attention for wearable devices in recent years. However, hydrogel suffers from limitations such as poor stretchability, freezing under cold climates, and drying out in harsh environments, which restrict its practical applications. To address these issues. We synthesize waterborne polyurethane (WPU) and add it to the polyvinyl alcohol (PVA) hydrogel to enhance its mechanical properties. Additionally, DMSO is introduced to the system, aiming to enhance the environmental stability of the hydrogel through its interaction with water. Hence, we prepare a novel organohydrogel by incorporating WPU into PVA in a dimethyl sulfoxide (DMSO)-water (H2O) binary solvent system by one-pot method. The addition of DMSO and WPU enhances the mechanical properties of the organohydrogel, resulting in high mechanical strength (1.27 MPa), excellent stretchability (874%), and superior toughness (3.62 MJ/m3). In addition, the organohydrogel presents reliable freeze resistance and water retention properties due to DMSO interaction with water. More significantly, the organohydrogel can be recycled and reshaped into various shapes through a simple process. The reconstructed organohydrogel still has the original's mechanical properties and sensing capabilities and can continue to be used in flexible electronic devices. Moreover, the organohydrogel is developed for flexible multifunctional sensors, exhibiting high sensitivity (G = 1.89), a rapid response time (141 ms), and exceptional fatigue resistance (100 cycles). Notably, the sensor signals remain stable even after storage in extreme conditions. This study expands the working field of flexible hydrogel sensors and provides a new idea for the sustainable development of next-generation flexible hydrogel sensors.

Abstract Composite polymer materials featured superior thermal conductivity, flame retardancy, and electromagnetic shielding performance are increasingly in demand due to the rapid development of highly miniaturized, portable, and flexible electronic devices. Herein, a facile and green ball milling shear method is utilized for generating MXene@Boron nitride (MXene@BN). The multi‐functional fillers (MXene@BN) are constructed and incorporated into polydimethylsiloxane (PDMS) to prepare a multifunctional composite (PDMS/MXene@BN) for achieving improved electromagnetic interference (EMI) shielding performance and thermal conductivity as well as flame retardancy simultaneously. When the PDMS/MXene@BN composite has a MXene@BN loading of 2.4 wt.%, it exhibits a high thermal conductivity of 0.59 W m−1K−1, which is 210% higher than that of the pure PDMS matrix. This is attributed to its unique chestnut‐like double‐layer structure. With a smoke production rate (SPR) of 0.04 m2 s−1 and total smoke production (TSP) of 3.51 m2, PDMS/MXene@BN 2.4 composite exhibits superb smoke suppression properties. These SPR and TSP values are 63.20% and 63.50% lower than the corresponding values of pure PDMS. Moreover, the EMI SE of the PDMS/MXene@BN 2.4 can reach 26.3 dB at 8.5 GHz. The work reported herein provides valuable insight into developing composites with multiple functions, which show strong potential for application in advanced packaging materials.

Currently, diverse hydrogels with multiple functionalities have attracted considerable attention. However, due to poor adaptability in real-life application scenarios for example in drying air and underwater, the hydrogels developed to date have not yet realized most of their promising applications, particularly in flexible electronics. Herein, inspired by the process of preparing the outermost layer of sugar coating on Tanghulu, a traditional Chinese winter snack, we report a dipping-ultraviolet (UV) encapsulation method for affording hydrogels with excellent water retention and anti-swelling capacity. A photoinitiator-grafted polymer chain (PGPC) with UV curing capability is prepared by 4-benzoylphenyl acrylate (ABP) and hydrophobic monomers radical polymerization, which is uncrosslinked during synthesis. After dipping and UV irradiation, the PGPC on the polyacrylamide (PAAm) hydrogel surface is cross-linked by benzophenone (BP) chemistry to form a coating network. Furthermore, the PGPC-coated hydrogel PAAm demonstrates great anti-drying properties with a weight fraction of up to 0.85 +/- 0.02 after 21 h at 50 degrees C and anti-swelling capacity with a weight fraction of down to 1.01 +/- 0.01 after 120 h in deionized water. Benefiting from the BP chemistry, the versatility of this method is demonstrated using various hydrogels such as polyvinyl alcohol (PVA) and polyzwitterionic hydrogel. As a proof-of-concept, the coated-hydrogel-based sensor shows strong signals anti-interference ability in ambient air and underwater. This work provides a promising route for encapsulating different hydrogels endowing weak hydrogels with strong environmental adaptability.

A combination effect of a polyurethane coating and hygroscopic lithium chloride endows various hydrogels with more adaptability to harsh environments.

A waterborne polyurethane pressure-sensitive adhesive (WPUPSA) has the advantages of low pollution and good viscoelasticity. However, its poor thermo-tolerance limits its application in the field of high temperatures. Hence, a novel silicone-modified strong thermo-tolerant waterborne polyurethane/polyimide pressure-sensitive adhesive is developed as a way to remedy this problem. The single-chain structure of waterborne polyurethane (WPU) is transformed into a network structure by introducing the three-position network structure to increase the cohesive energy and heat resistance of the WPUPSA. Meanwhile, the primary chain of waterborne polyurethane (WPU) is modified by the reaction between pyromellitic dianhydride (PMDA) and isophorone diisocyanate (IPDI) to include an imide ring and a benzene ring with more stable structures and heat resistance. Characterization results of the prepared WPUPSA show that the thermo-tolerance index of the WPUPSA increases by 15.2% and the room temperature 180° peel strength and shear resistance of the WPUPSA increase by 80.9 and 231.8%, respectively. Meanwhile, the temperature corresponding to the maximum thermal decomposition rate of the samples is improved. More importantly, at 80 and 100 °C, the 180° peel strength and shear resistance of the modified samples are stronger than those of the unmodified samples. In addition, the energy storage modulus of WPUPSAs is also greater than the loss and increases with the increase of the frequency. Viscoelasticity dominates in the samples. This will provide new insight for the development of WPUPSAs in the field of high-temperature resistance.

Although waterborne polyurethane pressure-sensitive (PSA) has achieved great progress, achieving robust effective adhesion on the wet substrate surface is still challenging. Herein, we developed a humidity-insensitive waterborne polyurethane pressure-sensitive adhesive through the modification of bio-based castor oil and 3-aminopropyl triethoxysilane (APTES) as the end-capper. Improved bonding property on wet substrate via drainage of hydrophobic groups led to better humidity-insensitive adhesiveness. The results exhibited exceptional bonding performance (similar to 3.3N/25 mm) on the moist surface of the steel in the environment with a humidity of 100 % RH (Relative Humidity). Especially, the 180 degrees peel forces of siloxane-terminated castor oil-based waterborne polyurethane (SCWPU) respectively enhanced by 13.33 % and 73.68 % compared with the blank sample when the air humidity increased from 50 % RH to 100 % RH. Silicone had the advantages of low surface energy, good heat resistance and good oxidation resistance. The heat resistance could be improved by introducing silicone into waterborne polyurethane. Tested by the TGA, the SCWPU3 PSA demonstrated great thermal stability (T-HRI=144.32 degrees C). Besides, the PSA also exhibited low water absorption (20.6 %), and eligible viscoelasticity properties. These findings provided an impetus for the development of humidity-insensitive PSA.

Cationic water-based polyurethane(CWPU) was synthesized to explore aloe-emodin modifies to obtain CWPU materials with better comprehensive performance. It provides a simple way to synthesize antibacterial waterborne polyurethane, which is to introduce the end-blocking group of herbal extracts into the structure. It contains synergistic antibacterial effect of herbal antibacterial and quaternary ammonium ion on Escherichia coli. It makes the material resist the erosion of bacterial, and increase the service life of materials. When the pH value of the environment changes, the UV absorbance of the aloe-emodin modified cationic water-based polyurethane(AE-CWPU) also changes. Therefore, within a certain detection range, AE-CWPU has great applications in the field of smart response materials. The modified thermodynamic properties have been improved, and the mechanical properties basically maintained the maximum stress, and the elongation at break was reduced.

The nanohybrid (BP-CMC) is prepared by amidation action between NH2-functionalized black phosphorus (NH2-BP) and carboxymethyl chitosan (CMC). The resulting BP-CMC is incorporated into cellulose nanofiber (CNF) by vacuum filtration to probe the flame-retardant and thermal conductivity performance. Microscale combustion calorimeter (MCC) exhibits the introduction of 30 wt% BP-CMC significantly promotes the flame-retardant property of CNF, for instance, 74.11% decline in heat release rate (HRR) and 91.31% decrease in total heat release (THR). Raman of residual chars further certificates the degree of graphitization is increased from 0.766 to 0.378 with 30 wt% incorperation of BP-CMC, isolating the transfer of oxygen and heat. The improvement of fire safety is attribute to the formation of an intumescent flame-retardant system, which is rich in carbon source (CMC), acid source (BP) and gas source (amino). Simultaneously, the introduction of 30wt% BP-CMC into CNF contributed to considerable enhancement in thermal conductivity (up to 17.49%), thermal diffusion (utmost to 43.45%) and heat capacity (increased by 19.23%). Moreover, the 30% addition amount of BP-CMC into CNF possesses excellent mechanical properties with improvement of toughness (increased by 143.50%) and tensile strength (increased by 140.90%). This strategy not only provides a new strategy for functionalizing BP, but also upgrade application potential of BP nanosheets in the fire proof of polymer composites.

In the past two decades, ionic conductive hydrogel has attracted tremendous research interests for their intrinsic characteristics in the field of flexible sensor. However, synchronous achievement of high mechanical strength, satisfied ionic conductivity, and broad adhesion to various substrates is still a challenge. Herein, a novel zwitterionic composite hydrogel that displayed excited strechability (up to 900%), satisfied strength (about 30 kPa), high ionic conductivity (1.2 mS cm(-1)), and adhesion to polar and nonpolar materials is fabricated though the combination of waterborne polyurethanes (PU) and poly(sulfobetaine zwitterion-co-acrylamide) (SAm). Especially, this facile strategy demonstrates that PU has a synergistic effect on enhancing mechanical strength and ionic conductivity for ionic conductive hydrogel. Moreover, the hydrogel-based strain/stress sensor shows high sensitivity, wide sensing range, great stability, and accuracy for human body movements detecting and voice recognition. This novel ionic conductive hydrogel has promoted the development of wearable devices.

Design and exploitation of smart fire-warning devices with ultrasensitive response capability are always an urgent need for effective fire protection. Herein, a nano-filler (BP-MoS2) is prepared by ball milling black phosphorene and molybdenum disulfide and added into the graphene oxide (GO) film to fabricate a multifunctional film with high fire resistance and rapid response ability. When the addition of BP-MoS2 is 20.0 wt%, the GO/BP-MoS2 20.0 shows an excellent flame retardancy. The residual char rate is improved from 46.60% to 66.65%, and its peak of heat release rate (pHRR) value has reduced from 599.92 W g(-1) to 274.00 W g(-1), resulting in a 54.33% decrease, which is attributed to the ultra-fast catalytic char formation and synergistic flame retardancy of BP and MoS2. Meanwhile, the composite film can still maintain the original shape within 15 s of ignition. More interestingly, when encountering a flame attack, it reveals an ultra-fast fire warning response (about 1 s), which is attributed to the fast carbonization after contacting with flame. Such approach offers a novel perspective for the preparation of intelligent fire alarm devices with ultra-fast response ability.

A multi-response flexible wearable strain sensor based on liquid metal and self-healing polyurethane with excellent sensitivity, reliability and durability is able to detect the full range of human motion and can sense stress and temperature.