Recent advances in conductive hydrogels: classifications, properties, and applications.

Hydrogel-based conductive materials for smart wearable devices have attracted increasing attention due to their excellent flexibility, versatility, and outstanding biocompatibility. This review presents the recent advances in multifunctional conductive hydrogels for electronic devices. First, conductive hydrogels with different components are discussed, including pure single network hydrogels based on conductive polymers, single network hydrogels with additional conductive additives (i.e., nanoparticles, nanowires, and nanosheets), double network hydrogels based on conductive polymers, and double network hydrogels with additional conductive additives. Second, conductive hydrogels with a variety of functionalities, including self-healing, super toughness, self-growing, adhesive, anti-swelling, antibacterial, structural color, hydrophobic, anti-freezing, shape memory and external stimulus responsiveness are introduced in detail. Third, the applications of hydrogels in flexible devices are illustrated (i.e., strain sensors, supercapacitors, touch panels, triboelectric nanogenerator, bioelectronic devices, and robot). Next, the current challenges facing hydrogels are summarized. Finally, an imaginative but reasonable outlook is given, which aims to drive further development in the future.

Investigation on a laser-assisted radiation thermometry technique.

A laser-assisted radiation thermometry (LART) technique is proposed for the surface temperature measurement of objects at high temperatures, which obviates the need for the knowledge of specimen emissivity. It uses a modulated laser to excite a temperature rise at the specimen surface, which is remotely sensed through thermal radiation detection at two infrared wavelengths. The theoretical analysis indicates that the surface temperature of the specimen can be inferred from the detected signals, independently of specimen emissivity. Measurements were performed on an oxidized Inconel 600 sample over a temperature range of 1120-1265 K. Measured surface temperatures were compared with those deduced from thermocouple measurements made inside the sample, and indicated less than 3% differences between them for sample surface temperatures above 1200 K.

A Robust Biomimetic Superhydrophobic Coating with Superior Mechanical Durability and Chemical Stability for Inner Pipeline Protection.

Durable superhydrophobic anti-erosion/anticorrosion coatings are highly demanded across various applications. However, achieving coatings with exceptional superhydrophobicity, mechanical strength, and corrosion resistance remains a grand challenge. Herein, a robust microstructure coating, inspired by the cylindrical structures situated on the surface of conch shell, for mitigating erosion and corrosion damages in gas transportation pipelines is reported. Specifically, citric acid monohydrate as a pore-forming agent is leveraged to create a porous structure between layers, effectively buffering the impact on the surface. As a result, the coating demonstrates remarkable wear resistance and water repellency. Importantly, even after abrasion by sandpaper and an erosion loop test, the resulting superhydrophobic surfaces retain the water repellency. The design strategy offers a promising route to manufacturing multifunctional materials with desired features and structural complexities, thereby enabling effective self-cleaning and antifouling abilities in harsh operating environments for an array of applications, including self-cleaning windows, antifouling coatings for medical devices, and anti-erosion/anticorrosion protection, among other areas.

Superhydrophobic polyurethane sponge for efficient water-oil emulsion separation and rapid solar-assisted highly viscous crude oil adsorption and recovery.

Rapid and efficient cleaning of oily wastewater and high viscosity crude oil spills is still a global challenge. Conventional three-dimensional porous adsorbents are ineffective for oil-water separation in harsh environment and are restricted to the low fluidity of high viscosity crude oil at room temperature. Increasing temperature can enormously improve the fluidity of viscous crude oil. Herein, the polydimethylsiloxane (PDMS) /carbon black (CB) -modified polyurethane sponge (PU) were prepared by a simple one-step dip-coating method. PDMS/CB@PU (PCPU) exhibits high adsorption capacity to various oils and organic liquid (28.5-68.7 g/g), strong mechanical properties (500 cycles at 50%), outstanding reusability (100 cycles of adsorption and desorption) and excellent environmental stability due to the special PDMS/CB coating. The maximum surface temperature of PCPU sponge can reach 84.7 â„ƒ under 1 sunlight irradiation. Therefore, the PCPU sponge can rapidly heat and enhance the fluidity of viscous crude oil, significantly speeding up the viscous oil recovery process with the maximum adsorption capacity of 44.7 g/g. In addition, the PCPU sponge can also combine with the vacuum pump to realize the continuous and rapid repair of viscous oil spills from the seawater surface. In consideration of its simple preparation, cost-effectiveness and high oil absorption ability, this solar-assisted self-heating adsorbent provides a new direction for large-scale cleanup and recycling of viscous crude oil spill on the seawater surface.

A Breathable Knitted Fabric-Based Smart System with Enhanced Superhydrophobicity for Drowning Alarming.

Wearable strain sensors have aroused increasing interest in human motion monitoring, even for the detection of small physiological signals such as joint movement and pulse. Stable monitoring of underwater human motion for a long time is still a notable challenge, as electronic devices can lose their effectiveness in a wet environment. In this study, a superhydrophobic and conductive knitted polyester fabric-based strain sensor was fabricated via dip coating of graphene oxide and polydimethylsiloxane micro/nanoparticles. The water contact angle of the obtained sample was 156°, which was retained above 150° under deformation (stretched to twice the original length or bent to 80°). Additionally, the sample exhibited satisfactory mechanical stability in terms of superhydrophobicity and conductivity after 300 abrasion cycles and 20 accelerated washing cycles. In terms of sensing performance, the strain sensor showed a rapid and obvious response to different deformations such as water vibration, underwater finger bending, and droplet shock. With the good combination of superhydrophobicity and conductivity, as well as the wearability and stretchability of the knitted polyester fabric, this wireless strain sensor connected with Bluetooth can allow for the remote monitoring of water sports, e.g., swimming, and can raise an alert under drowning conditions.

Flexible and Highly Conductive Textiles Induced by Click Chemistry for Sensitive Motion and Humidity Monitoring.

To date, multifunctional sensors have aroused widespread concerns owing to their vital roles in the healthcare area. However, there are still significant challenges in the fabrication of functionalized integrated devices. In this work, hydrophobic-hydrophilic patterns are constructed on polyester-spandex-blended knitted fabric surface by the chemical click method, enabling accurate deposition of functionalized materials for sensitive and stable motion and humidity sensing. Representatively, a conductive silver nanowire (Ag NW) network was deliberately deposited on only the designated hydrophilic fabric surface to realize accurate, repeatable, and stable motion sensing. Such a Ag NWs sensor recorded a low electrical resistance (below 60 Ω), stable resistance cycling response (over 2000 cycles), and fast response time to humidity (0.46 s) during the sensing evaluation. In addition to experimental sensing, real human motions, such as mouth-opening and joint-flexing (wrist and neck), could also be detected using the same sensor. Similar promising outputs were also obtained over the humidity sensor fabricated over the same chemical click method, except the sensing material was replaced with polydopamine-modified carboxylated carbon nanotubes. The resultant sensor exhibits excellent sensitivity to not only experimentally adjusted environment humidity but also to the moisture content of breath and skin during daily activities. On top of all these, both sensors were fabricated over highly flexible fabric that offers high wearability, promising great application potential in the field of healthcare monitoring.

Underwater, Multifunctional Superhydrophobic Sensor for Human Motion Detection.

Superhydrophobic conductive materials have received a great amount of interest due to their wide applications in oil-water separation, electrically driven smart surface, electromagnetic shielding, and body motion detection. Herein, a highly conductive superhydrophobic cotton cloth is prepared by a facile method. A layer of polydopamine/reduced graphene oxide (PDA/rGO) was first coated on the cotton fabric, and then copper nanoparticles were in situ grown on the prepared surface. After further modification with stearic acid (STA), the wettability of the cotton surface changed from superhydrophilic to superhydrophobic (water contact angle (WCA) = 153°). The electrical conductivity of the PDA/rGO/Cu/STA cotton is as high as 6769 S·m-1, while the stearic acid effectively protects Cu NPs from oxidation. As a result, the superhydrophobic PDA/rGO/Cu/STA cotton has shown excellent electrical stability and can be used in detecting human motions in both ambient and underwater conditions. The sensor can recognize human motion from air into water and other underwater activities (e.g., underwater bending, stretching, and ultrasound). This multifunctional cotton device can be used as an ideal sensor for underwater intelligent devices and provides a basis for further research.

Robust Superhydrophobic rGO/PPy/PDMS Coatings on a Polyurethane Sponge for Underwater Pressure and Temperature Sensing.

Flexible wearable pressure sensors have attracted great interest from researchers in recent years because of their important applications in human-machine interaction, human behavior detection, medical diagnosis, and other fields. At present, integrating multiple functions such as pressure and temperature sensing and self-cleaning into a single material remains a challenging task. Here, by in situ reduction of graphene oxide (GO) grown on a sponge surface and deposition of polypyrrole (PPy) nanoparticles, we have built a highly sensitive, stable, and multifunctional rGO/PPy/poly(dimethylsiloxane) (PDMS) polyurethane (PU) sponge (GPPS) sensor for the detection of pressure, water level, and temperature. This multifunctional sensor shows excellent pressure-sensing performance, ultrasensitive loading sensing of a leaf (98 mg), and outstanding reproducibility over 5000 cycles. Due to the stability of the superhydrophobic surface water contact angle (WCA) = 153.3°, our sensor can work in an underwater environment, which can sense water levels from 1 cm (∼98 Pa) to 40 cm and also a variety of underwater behaviors (knock, ultrasonication, blow, etc.) with high stability. In addition, the sensor can be integrated into a circuit for the water level and pressure detection. The sensor can also be used as a smart underwater-temperature sensor; it shows a linear temperature coefficient of resistance (TCR) of 0.48% °C-1 in a temperature range of 35-80 °C. This multifunctional sensor shows potential application prospects in wearable electronic devices for sensing.