Aramid fibers (AFs) are widely applied in many cutting-edge fields, due to their excellent comprehensive performance. Ongoing research efforts are therefore underway to expand the applicability by designing more environmentally friendly and low-cost synthesis methods, incorporating new chemical components in the skeletons or internal structures of polyamide to enhance their processability and functionality. Despite being at the forefront of scientific research, there are fewer reviews that comprehensively summarize the latest progress of AFs. This review focuses on the fundamental research of AFs since their inception and summarizes the advanced progress and applications of AFs. Firstly, the synthesis mechanism and methods of AFs and their structure–property relationship are comprehensively discussed. Subsequently, we review the recent progress in surface functionalization of AFs by using advanced micro-nanoscale modification strategies to enhance the interface properties and ultraviolet (UV)-resistance properties, and summarize the advantages and disadvantages of various modified methods. Then, applications of AF and aramid nanofiber (ANF) in various fields are discussed. Finally, the possible challenges and outlooks toward the future development of AFs are highlighted, which is expected to provide new insights for the next-generation advanced functional AF materials and facilitate the industrialization development level for high-performance AFs and their composites.
The intelligent textile sensors based on fiber (1D) and fabric (2D) are the ideal candidates for wearable devices. Their flexible weaving and unique structure endow them with flexibility, lightweight, good air permeability, and feasible integration with garments. In view of the spring-up of novel textile-based strain sensors, the novel materials and fabrication approaches were elaborated from spatial perspectives, i.e., 1D fibers/yarn and 2D fabric. The intrinsic sensing mechanism is the primary factor affecting sensor sensitivity, and the variation trend of the sensing signal is closely related to it. Although existing studies have involved various sensing mechanisms, there is still lacking systematic classification and discussion. Hence, the sensing mechanisms of textile-based sensors were elaborated from spatial perspectives. Considering that strain sensors were mostly based on resistance variation, the sensing mechanisms of resistive textile-based strain sensors were mainly focused, mainly including fiber deformation, tunneling effect, crack propagation, fabric deformation, electrical contact and bridge connection. Meanwhile, the corresponding resistance prediction models, usually used as important data fitting methodology, were also comprehensively discussed, which can reproduce the resistance trend and provide guidance for the sensor performance. Finally, the multifunctionality of textile-based strain sensors was summarized, namely multi-mode signal detection, visual interaction, energy collection, thermal management and medical treatment were discussed. It was expected to provide research insights into the multifunctional integration of textile sensors.
Nanocomposite fibers are fibrous materials with specific properties and functionalities, which are prepared by introducing nanomaterials or nanostructures in the fibers. Polymeric nanocomposite fibers exhibit multiple functionalities, showing great application potential in healthcare, aerospace, mechanical engineering, and energy storage. Here, six functionalities of polymer nanocomposite fibers are reviewed: mechanical reinforcement, resistance to electromagnetic interference and flame, thermal and electrical conduction, generation of far-infrared ray, negative ion and electricity, energy storage, and sensing. For each functionality, the fiber component selection and preparation methods are summarized. The commonly used polymers comprise natural and synthetic polymers, and typical nanomaterials include carbon-based, polymer-based, metal-based, and metal oxide-based ones. Various compounding strategies and spinning approaches, such as wet-spinning, melt-spinning, and electrospinning, are introduced. Moreover, the functional properties of fibers fabricated from different constituents and by different strategies are compared, providing a reference for performance optimization. Finally, the prospective directions of research and application are discussed, and possible approaches are suggested to facilitate the development of advanced nanocomposite fibers.
Binder-free electrospining approach for fabricating bimetallic chalcogen electrodes is essential for cost- and time-cutting but challenging. Herein, we propose a novel direct spray technique in electrospinning method to fabricate binder-free electrospun nickel cerium selenide nanofiber (NCSNF) structured materials. The effect of the applied electrospinning voltage on the average fiber diameter is analyzed. Electrospinning voltage of 25 kV is applied for obtaining an average fiber diameter of < 100 nm (87 nm) with rough interconnected nanofibers. The optimized NCSNF electrode exhibits remarkable long-term cycling stability over 50,000 galvanostatic charge–discharge (GCD) cycles. Furthermore, radish-derived nanolayered carbon (RDNLC) is synthesized via pyrolysis and its electrochemical properties are evaluated. The optimized NCSNF and RDNLC electrodes are employed to fabricate a polyvinyl alcohol–potassium hydroxide gel electrolyte-based quasi-solid-state asymmetric supercapacitor (ASC). The quasi-solid-state ASC delivers a high energy density value of 22 Wh kg−1 with 85% capacitance retention and 95% Coulombic efficiency over 40,000 GCD cycles, and upon being extended to the 50,000 GCD cycles, the capacitance retention and Coulombic efficiency reached 71% and 95%, respectively. A solar-charged wristband-like device is designed as a wearable supercapacitor, and the integrated device is attached to the human hand for powering electronic gadgets in contorted states, thus demonstrating its potential for wearable applications.
Wearable piezoresistive sensors have shown enormous application prospects in flexible electronics and human–machine interfaces. However, current piezoresistive sensors suffer from common deficiencies including high fabrication cost, poor comfort and low attachment fastness of conductive substances on substrates, thereby impeding their large-scale production and practical use. Herein, a three-dimensional all-fabric piezoresistive sensor is reported based on coating multi-wall carbon nanotubes (MWCNTs) on bicomponent nonwovens composed of core-sheath fibers. The combination of core-sheath fibers with a heat-induced welding strategy greatly improves the adhesion fastness and stability of MWCNT network. The multi-layered all-fabric structure provides as-prepared sensors with high sensitivity (9.43% kPa−1 in 0–10 kPa and 0.076% kPa−1 in 20–120 kPa), wide pressure-sensing range (0–120 kPa), fast response/relaxation time (100 and 60 ms), good reproducibility and air permeability. Application of the sensor is demonstrated through the detection of human activities (such as pulse, cough and joint movements) and the wireless monitoring of forefinger bending. Moreover, our sensor is fabricated out of cost-effective materials, using scalable approach without using glue or binders. The method established in this work may provide an efficient strategy for the design and production of high-performance all-fabric piezoresistive sensors.
Piezoelectric nanofibers have received extensive attention in the field of electronic devices, but they are still restricted for further development, due to their limited dipole arrangement. Herein, we propose spatially confined MXene/polyvinylidene fluoride (PVDF) nanofibers for piezoelectric application, with dual functions of pressure sensing and energy harvesting. The spatial confinement of MXene/PVDF nanofibers can actively induce the optimally aligned –CH2–/–CF2– dipoles of PVDF and dramatically boost spontaneous polarization for piezoelectric enhancement. The voltage and current generated by fabricated MXene/PVDF (0.8 wt%) nanofiber piezoelectric electronic devices are respectively 3.97 times and 10.1 times higher than those generated by pure PVDF nanofibers. Based on these results, the developed bifunctional electronic devices are applied to monitor various human movements and to harvest energy. Notably, the results of this work allow for the development of nanofibers with excellent piezoelectric performance using a spatial confinement mechanism.
Highly stable hydrophobic silica-based membranes were successfully fabricated through chemical post-modification of directly electrospun silica nanofibrous membranes. Five different Si-alkoxy chlorides were tried as reagents at room temperature, allowing for an easy two-step production process. Trimethylchlorosilane (TMCS) was determined as to be the most suitable modifier, for this purpose. The modified membrane exhibits long-term hydrophobicity even under high humidity and water submersion, maintaining this property after exposure to elevated temperatures and acidic conditions, surpassing the unmodified membrane. The separation effectiveness for immiscible water/solvent solutions was proven, followed by an investigation into the relation between the surface tension of some miscible water/solvent solutions and the resulting wetting behavior of the TMCS-modified membrane, to utilize the membrane as a process intensification tool, specifically as a solvent gate.
Ruthenium phosphide is a promising catalyst for hydrogen evolution due to its cost-effectiveness compared to platinum. However it faces the challenge of having a high binding energy for hydrogen intermediates. In this study, we demonstrate that the incorporation of iridium in ruthenium phosphides lowers the binding energy of hydrogen intermediates, thereby controlling the overpotential and Tafel slope of hydrogen evolution. When the Ir content was doped at 3 at.%, the catalyst achieved an overpotential of 33 mV and a Tafel slope of 33 mV dec−1 under acidic conditions, which are similar to those of the benchmark Pt/C catalyst. In situ Raman spectroscopy and density functional theory (DFT) calculations suggest that the enhanced catalytic activity originates from the near-neutral Gibbs free energy of hydrogen adsorption on the hollow site of the iridium cluster implanted onto ruthenium phosphide.
Stretchable thermoelectric-based self-powered sensors have attracted widespread attention for wearable electronic devices. However, the development of thermoelectric materials with wearable comfort, green, and multimodal synergy remains challenging. In this paper, we prepared a poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube (PEDOT/MWCNT)-based thermoelectric fabric for self-powered strain–temperature dual-parameter sensing via spraying and in situ bio-polymerization. Compared with ferric chloride (FeCl3), used in chemical polymerization, the PEDOT thermoelectric fabric prepared by enzymatic polymerization is not doped with metal ions, making the thermoelectric performance of flexible wearable fabrics more stable. In addition, the energy-filtration effect of PEDOT and MWCNT efficiently enhanced the thermoelectric performance of the fabric. The fabric has over 320% elongation potential and excellent breathability while exhibiting excellent wearability. Moreover, the fabric-based sensor had a wide strain range (1–100%) and temperature detection limit (1 °C). In addition, fabric-based sensors were tested by sewing them directly onto clothing or attachment accessories, and showed a rapid response to changes in human joint bending and microenvironmental temperature differences. Moreover, the sensor could be integrated into an intelligent firefighting suit, to continuously and synergistically monitor health abnormalities in firefighter's body movement and temperature thresholds in the micro-environmental temperature of the suit. The developed self-powered dual-parameter wearable sensor shows fascinating potential for applications in human health monitoring, human–computer interaction devices, and intelligent robotics.
The uncontrolled dendrite growth and shuttle effect of polysulfides have hindered the practical application of lithium–sulfur (Li–S) batteries. Herein, a metal–organic framework-derived Ag/C core–shell composite integrated with a carbon nanofiber film (Ag/C@CNF) is developed to address these issues in Li-S batteries. The Ag/C core–shell structure design endows the CNF skeleton with enhanced electrical conductivity, electrocatalysis performance toward polysulfides conversion, and lithium nucleation. When served as a freestanding bifunctional host in Li-S batteries, the Ag/C@CNF composite regulates the Li and sulfur electrochemical processes by guiding the uniform Li deposition with mitigated dendrite growth and at the same time accelerating the polysulfides conversion. The assembled Li–S full battery delivers a considerable capacity of 650 mAh g−1, an ultralong cyclability with an attenuation rate as low as 0.02% per cycle for 1000 cycles at 5 C, and excellent rate performances at increased sulfur loading up to 7.6 mg cm−2 under lean electrolyte condition.
Ionogels have enabled flexible electronic devices for wide-ranging innovative applications in wearable electronics, soft robotics, and intelligent systems. Ionogels for flexible electronics need to essentially tolerate stress, temperature, humidity, and solvents that may cause their electrical conductivity, structural stability, processing compatibility and sensibility failure. Herein, we developed a novel in-situ photopolymerization protocol to fabricate intrinsically conductive, self-gated ionogels via ion-restriction dual effects. Highly sensitive and intelligent safety sensors with tunable stretchability, robust chemical stability, favorable printability, and complete recyclability, are programmed from defined microneedle arrays printed by the intrinsically conductive ionogel. Ultrahigh elasticity (~ 794% elongation), high compression tolerance (~ 90% deformation), improved mechanical strength (tensile and compressive strength of ~ 2.0 MPa and ~ 16.3 MPa, respectively) and remarkable transparency (> 91.1% transmittance), as well as high-temperature sensitivity (− 2.07% °C−1) and a wide working range (− 40 to 200 °C) can be achieved. In particular, the intrinsic sensing mechanisms of ion-restriction dual effects are unlocked based on DFT calculations and MD simulations, and operando temperature-dependent FTIR, and Raman technologies. Moreover, the real-time intelligent monitoring systems toward physical signals and precise temperature based on the microneedle array-structures sensors are also presented and demonstrate great potential applications for extreme environments, e.g., fire, deep-sea or aerospace.
Thick cathodes can overcome the low capacity issues, which mostly hamper the performance of the conventional active cathode materials, used in rechargeable Li batteries. However, the typical slurry-based method induces cracking and flaking during the fabrication of thick electrodes. In addition, a significant increase in the charge-transfer resistance and local current overload results in poor rate capabilities and cycling stabilities, thereby limiting electrode thickening. In this study, a synergistic dual-network combination strategy based on a conductive nanofibrillar network (CNN) and a nano-bridging amorphous polyhydroxyalkanoate (aPHA) binder is used to demonstrate the feasibility of constructing a high-performance thick cathode. The CNN and aPHA dual network facilitates the fabrication of a thick cathode (≥ 250 μm thickness and ≥ 90 wt% active cathode material) by a mass-producible slurry method. The thick cathode exhibited a high rate capability and excellent cycling stability. In addition, the thick cathode and thin Li metal anode pair (Li//t-NCM) exhibited an optimal energy performance, affording high-performance Li metal batteries with a high areal energy of ~ 25.3 mW h cm−2, a high volumetric power density of ~ 1720 W L−1, and an outstanding specific energy of ~ 470 W h kg−1 at only 6 mA h cm−2.
TOC figure: Synergistic combination of a conductive nano-fibrillar network (CNN) and nano-bridging amorphous polyhydroxyalkanoate (aPHA) binder that affords the high-performance cathode with ≥ 250 μm thickness and ≥ 90 wt% active cathode material. Li-metal batteries (Li//t-NCM) based on thick cathodes and thin Li exhibit outstanding energy storage performance.
Noninvasive human augmentation, namely a desirable approach for enhancing the quality of life, can be achieved through wearable electronic devices that interact with the external environment. Wearable electronic devices endure limitations, such as unreliable signal interaction when bent or deformed, excessive wiring requirements, and lack of programmability and multifunctionality. Herein, we report an intelligent and programmable (IP) fabric sensor with bending insensitivity that overcomes these challenges associated with a rapid response time (< 400 μs) and exceptional durability (> 20,000 loading–unloading cycles). A single-layer parallel electrical bilateral structure is utilized to design the IP fabric sensor with reconfigurability and only two electrodes, which caters to the requirement of stable interactions and simple wiring. The multifunctionality of the IP fabric sensor is demonstrated by designing a closed-loop interactive entertainment system, a smart home system, and a user identification and verification system. This integrated system reveals the potential of combining Internet of Things technology and artificial intelligence (AI). Hopefully, the integration of the noninvasive IP fabric sensor with AI will facilitate the advancement of interactive systems for human augmentation.
Given the abundant solar light available on our planet, it is promising to develop an advanced fabric capable of simultaneously providing personal thermal management and facilitating clean water production in an energy-efficient manner. In this study, we present the fabrication of a photothermally active, biodegradable composite cloth composed of titanium carbide MXene and cellulose, achieved through an electrospinning method. This composite cloth exhibits favorable attributes, including chemical stability, mechanical performance, structural flexibility, and wettability. Notably, our 0.1-mm-thick composite cloth (RC/MXene IV) raises the temperature of simulated skin by 5.6 °C when compared to a commercially available cotton cloth, which is five times thicker under identical ambient conditions. Remarkably, the composite cloth (RC/MXene V) demonstrates heightened solar light capture efficiency (87.7%) when in a wet state instead of a dry state. Consequently, this cloth functions exceptionally well as a high-performance steam generator, boasting a superior water evaporation rate of 1.34 kg m−2 h−1 under one-sun irradiation (equivalent to 1000 W m−2). Moreover, it maintains its performance excellence in solar desalination processes. The multifunctionality of these cloths opens doors to a diverse array of outdoor applications, including solar-driven water evaporation and personal heating, thereby enriching the scope of integrated functionalities for textiles.