RESUMEN
MXenes have exhibited potential for application in flexible devices owing to their remarkable electronic, optical, and mechanical properties. Printing strategies have emerged as a facile route for additive manufacturing of MXene-based devices, which relies on the rational design of functional inks with appropriate rheological properties. Herein, aqueous MXene/xanthan gum hybrid inks with tunable viscosity, excellent printability, and long-term stability are designed. Screen-printed flexible MXene films using such hybrid inks exhibit a high conductivity up to 4.8 × 104 S m-1 , which is suitable to construct multifunctional devices mainly including electromagnetic shielding, Joule heaters, and piezoresistive sensors. The average electromagnetic interference (EMI) shielding value can reach to 40.1 dB. In the Joule heater, the heating rate of printed MXene film can reach 20 °C s-1 under a driving voltage of 4 V, with a highest steady-state temperature of 130.8 °C. An MXene-based piezoresistive sensor prepared by the printing interdigital electrode also presents good sensing performance with a short response time of 130 ms and wide pressure region up to 30 kPa. As a result, screen-printed MXene film exhibits reinforced multifunctional performance, which is promising for application in the next-generation of intelligent and wearable devices.
RESUMEN
High-efficiency electromagnetic interference (EMI) shielding and heat dissipation synergy materials with flexible, robust, and environmental stability are urgently demanded in next-generation integration electronic devices. In this work, we report the lamellar MXene/Aramid nanofiber (ANF) composite films, which establish a nacre-like structure for EMI shielding and heat dissipation by using the intermittent filtration strategy. The MXene/ANF composite film filled with 50 wt % MXene demonstrates enhanced mechanical properties with a strength of 230.5 MPa, an elongation at break of 6.2%, and a toughness of 11.8 MJ·m3 (50 wt % MXene). These remarkable properties are attributed to the hydrogen bonding and highly oriented structure. Furthermore, due to the formation of the MXene conductive network, the MXene/ANF composite film shows an outstanding conductivity of 624.6 S/cm, an EMI shielding effectiveness (EMI SE) of 44.0 dB, and a superior specific SE value (SSE/t) of 18847.6 dB·cm2/g, which is better than the vacuum filtration film. Moreover, the MXene/ANF composite film also shows a great thermal conductivity of 0.43 W/m·K. The multifunctional MXene/ANF composite films with high-performance EMI shielding, heat dissipation, and joule heating show great potential in the field of aerospace, military, microelectronics, microcircuit, and smart wearable electronics.
RESUMEN
Among the increasingly popular miniature and flexible smart electronics, two-dimensional materials show great potential in the development of flexible electronics owing to their layered structures and outstanding electrical properties. MXenes have attracted much attention in flexible electronics owing to their excellent hydrophilicity and metallic conductivity. However, their limited interlayer spacing and tendency for self-stacking lead to limited changes in electron channels under external pressure, making it difficult to exploit their excellent surface metal conductivity. We propose a strategy for rapid gas foaming to construct interlayer tunable MXene aerogels. MXene aerogels with rich interlayer network structures generate maximized electron channels under pressure, facilitating the effective utilization of the surface metal properties of MXene; this forms a self-healable flexible pressure sensor with excellent sensing properties such as high sensitivity (1,799.5 kPa-1), fast response time (11 ms), and good cycling stability (>25,000 cycles). This pressure sensor has applications in human body detection, human-computer interaction, self-healing, remote monitoring, and pressure distribution identification. The maximized electron channel design provides a simple, efficient, and scalable method to effectively exploit the excellent surface metal conduction of 2D materials.
RESUMEN
With the increasing popularity of smart wearable devices, flexible pressure sensors are highly desired in various complex application scenarios. A great challenge for existing flexible pressure sensors is to maintain high sensitivity over a wide temperature range, which is critical for their applications in harsh environments. Herein, a flexible piezoresistive sensor made of polyetherimide (PEI) fibrous network evenly covered with MXene nanosheets is reported to construct conductive pathways, showing ultrahigh sensitivity over a wide temperature range from -5 °C (sensitivity of 80 kPa-1 ) to 150 °C (20 kPa-1 ), low detection limit of 9 Pa, fast response time of 163 ms, outstanding durability over 10 000 cycles at room temperature, 2000 cycles at 100 °C and 500 cycles at -5 °C. The pressure sensor can monitor various human activities in real-time, apply to human-machine interaction, and measure pressure distribution. It also can sensitively respond to external mechanical stimuli at 150 °C and extremely low temperature (in liquid nitrogen). Moreover, the fibrous network exhibits an excellent Joule heating performance, which can reach 78 °C at an applied voltage of 12 V. Thus, the piezoresistive sensor has considerable potential for wearable garments and personal heating applications in harsh temperature conditions.
RESUMEN
Polymer nanocomposites with nanoparticles dispersed in polymer matrices have attracted extensive attention due to their significantly improved overall performance, in which the nanoparticle-polymer interface plays a key role. Understanding the structures and properties of the interfacial region, however, remains a major challenge for polymer nanocomposites. Here, we directly observe the presence of two interfacial polymer layers around a nanoparticle in polar polymers, i.e., an inner bound polar layer (~10 nm thick) with aligned dipoles and an outer polar layer (over 100 nm thick) with randomly orientated dipoles. Our results reveal that the impacts of the local nanoparticle surface potential and interparticle distance on molecular dipoles induce interfacial polymer layers with different polar molecular conformations from the bulk polymer. The bilayer interfacial features lead to an exceptional enhancement in polarity-related properties of polymer nanocomposites at ultralow nanoparticle loadings. By maximizing the contribution of inner bound polar layer via a nanolamination design, we achieve an ultrahigh dielectric energy storage density of 86 J/cm3, far superior to state-of-the-art polymers and nanocomposites.
RESUMEN
Prevalent irregular rainfall, flooding for weed control, and unleveled fields in the middle and lower reaches of the Yangtze River all contribute to flooding stress on germination and growth of direct-seeded rice (Oryza sativa L.). Herein, some experiments were conducted so as to assess the effects of seed priming with selenium (Se) on the germination and growth of rice under hypoxia. The experiment was arranged in a completely randomized factorial design with two factors and five replicates. Factors included Se concentration (0, 30, and 60 µmol/L) and duration of flooding stress (0, 2, 4, and 8 days). The experimental results showed that Se accelerated seed germination and increased emergence index and final emergence percentage. Additionally, Se increased shoot and root lengths and dry weights, but high Se concentration (60 µmol/L) reduced 18-day-old seedling dry weight under long-term flooding (8 days). Furthermore, Se reduced malondialdehyde content and increased starch hydrolysis efficiency in seeds, superoxide dismutase, peroxidase, catalase, and glutathione peroxidase activities and seedling soluble protein and total chlorophyll contents. Se improved seedling total Se and organic Se contents while increasing total dry weight and yield. Notably, the highest yield was obtained after a 4-day flooding period. Although Se priming favored rice seedling emergence and growth under flooding conditions, Se concentrations equal or above 60 µmol/L increased the risk of seedling death during long-term flooding (≥8 days).
RESUMEN
Two-dimensional transition-metal carbides (MXenes) have superhydrophilic surfaces and superior metal conductivity, making them competitive in the field of electrochemical energy storage. However, MXenes with layered structures are easily stackable, which reduces the ion accessibility and transport paths, thus limiting their electrochemical performance. To fully exploit the advantages of MXenes in electrochemical energy storage, this study reports the etching of large-sized MXene into nanosheets with nanoscale ion channels via a chemical oxidation method. While the resulting ion-channel MXene electrodes retain the excellent mechanical strength and electrical conductivity of large-sized MXene nanosheets, they can effectively shorten the ion transport distance and improve the overall electrochemical activity. The fabricated self-healing MXene-based zinc-ion microcapacitor exhibits a high areal specific capacitance (532.8 mF cm-2) at the current density of 2 mA cm-2, a low self-discharge rate (4.4 mV h-1), and high energy density of 145.1 µWh cm-2 at the power density of 2800 µW cm-2. The proposed nanoscale ion channel structure provides an alternative strategy for constructing high-performance electrochemical energy storage electrodes, and has great application prospects in the fields of electrochemical energy storage and flexible electronics.