Flexural Properties and Failure Mechanisms of Short-Carbon-Fiber-Reinforced Polylactic Acid Composite Modified with MXene and GO.

Recently, short-fiber-reinforced thermoplastic composites (SFRTPCs) have been playing a more and more crucial role in the application of automotive interior materials due to their advantages of low density and environmental resistance properties. However, their relevant mechanical properties need to be optimized. Previous investigations revealed that the surface modification of fibers is useful to improve their mechanical properties. In this work, carbon fiber (CF)-reinforced polylactic acid (PLA) composites modified with MXene and graphene oxide (GO) were prepared by twin-screw extrusion and injection molding methods. Short CF was firstly modified with polyetherimide (PEI), then different weight ratios of MXene-GO (1:1) were subsequently modified on PEI-CF. Finally, the flexural properties and failure mechanisms were analyzed. The results showed that MXene-GO was successfully coated on CF surface, and the flexural strength and modulus of CF-PEI-MXene-GO-reinforced PLA (CF-PEI-MG/PLA) composite were improved compared to that of CF/PLA composite. In addition, the fracture sections of the composites were flat and white, and the fibers bonded well with PLA for CF-PEI-0.1MG/PLA composite compared to CF/PLA composite. The present study could provide a reference for further improving the mechanical performance of PLA-related composites.

Enabling Further Organic Electrolyte Infiltration of Cellulose-Based Separators via Defect-Rich Polypyrrole Modification for High Sodium Ion Transport in Sodium Metal Batteries.

Sodium metal batteries (SMBs) have high-density and cost-effective characteristics as one of the energy storage systems, but uncontrollable dendrite growth and poor rate performance still hinder their practical applications. Herein, a nitrogen-rich modified cellulose separator with released abundant ion transport tunnels in organic electrolyte was synthesized by in situ polymerization of polypyrrole, which is based on the high permeability of cellulose in aqueous solution and the interfacial interaction between cellulose and polypyrrole. Meanwhile, the introduction of abundant structural defects such as branch chains, oxygen-containing functional groups, and imine-like structure to disrupt polypyrrole conjugation enables the utilization of conductive polymers in composite separator applications. With the electrolyte affinity surface on, the modified separator exhibits reinforced electrolyte uptake (254%) and extended electrolyte wettability, thereby leading to accelerated ionic conductivity (2.77 mS cm-1) and homogeneous sodium deposition by facilitating the establishment of additional pathways for ion transport. Benefiting from nitrogen-rich groups, the polypyrrole-modified separator demonstrates selective Na+ transport by the data of improved Na+ transference number (0.62). Owing to the above advantages, the battery assembled with the modified separators exhibits outstanding rate performance and prominent capacity retention two times that of the pristine cellulose separator at a high current density under the condition of fluorine-free electrolyte.

Advances in Ablation or Oxidation Mechanisms and Behaviors of Carbon Fiber-Reinforced Si-Based Composites.

Composites with excellent thermomechanical and thermochemical properties are urgently needed in the aerospace field, especially for structural applications under high-temperature conditions. Carbon fiber-reinforced Si-based composites are considered the most promising potential high-temperature materials due to their excellent oxidation resistance and ablative behaviors, good structural designability, and excellent mechanical properties. The reinforcement of the relevant composites mainly involves carbon fiber, which possesses good mechanical and temperature resistance abilities. In this paper, the ablation behaviors and mechanisms of related composites are reviewed. For carbon fiber-reinforced pure Si-based composites (C/SiM composites), the anti-ablation mechanism is mainly attributed to the continuous glassy SiO2, which inhibits the damage of the substrate. For C/SiM composite doping with refractory metal compounds, the oxides of Si and refractory metal together protect the main substrate from ablation and oxidation. Moreover, in addition to thermochemical damage, thermophysical and thermomechanical behavior severely destroy the surface coating of the substrate.

Scalable Quasi-Solid-State Supercapacitor for Wide-Temperature Wearable Devices.

Quasi-solid-state supercapacitors have wide application prospects in flexible and scalable electronics, which require high capacity, simple form factor, and excellent mechanical robustness. However, it is a challenge to have all these benefits in one material. Addressing this, we report a composite hydrogel with excellent mechanical durability and freezing resistance. The designed composite hydrogel acts both as a load-bearing layer to maintain its structure during deformation and as a permeable binder to stimulate the interfacing between the conductive electrode and the electrolyte to reduce the interface resistance. Flexible supercapacitors are assembled with composite hydrogels and high-performance MnO2/carbon cloth, which has excellent performance and can store energy at different temperatures or bending states. These results show that the tough hydrogel facilitates the improvement of electrical and mechanical stability, showing great potential in wide-temperature wearable devices.

Long-Cycle-Life Sodium-Ion Battery Fabrication via a Unique Chemical Bonding Interface Mechanism.

Titanates have been widely reported as anode materials for sodium-ion batteries (SIBs). However, their wide temperature suitability and cycle life remain fundamental issues that hinder their practical application. Herein, a novel hollow Na2 Ti3 O7 microsphere (H-NTO) with a unique chemically bonded NTO/C(N) interface is reported. Theoretical calculations demonstrated that the NTO/C(N) interface stabilizes the crystal structure, and the optimized interface enables the H-NTO anode to stably operate for 80 000 cycles in a conventional ester electrolyte with negligible capacity loss. Optimizing the electrolyte allows the H-NTO electrode to cycle stably for 200 calendar days without capacity degradation at -40 °C. The excellent cycling stability is attributed to the NTO/C(N) interface and the stable solid electrolyte interphase formed by the highly adaptable electrolyte/electrode interface. Titanate exhibits solvent co-intercalation behavior in ether-based electrolytes, and its robust structure ensures that it can adapt to large volume changes at low temperatures. This study provides a unique perspective on the long-cycle mechanism of titanate anodes and highlights the critical importance of manipulating the interfacial chemistry in SIBs, including the material and electrode/electrolyte interfaces.

Adhesive, antibacterial and double crosslinked carboxylated polyvinyl alcohol/chitosan hydrogel to enhance dynamic skin wound healing.

An available dressing material which promotes skin tissue repair is of significant importance for public health. Moreover, dynamic wounds have special requirements for hydrogel dressings due to their motion state. Correspondingly, a double crosslinked hydrogel was prepared based on amide and coordination bonds from carboxylated polyvinyl alcohol (PC) and chitosan (CS)/Fe3+. The hydrogel exhibited excellent swelling ratio and suitable biodegradability, which is beneficial to the tissue repair. The results showed that hydrogels with crosslinked structure possessed better unique properties, such as stronger mechanical (78 kPa of G') and adhesion properties, and shorter self-healing time (5 mins), the change of which was consistent with dynamic wounds. The hydrogel exhibited not only antibacterial activity (98 % fatality rate), but also superior hemostatic capacity during the wound healing process. In addition, the hydrogel could shorten skin healing time to 14 days, and obviously accelerated skin structure reconstruction by promoting angiogenesis and collagen deposition. Therefore, double crosslinked hydrogel is a promising dynamic wound dressing.

Flexible, high-strength and multifunctional polyvinyl alcohol/MXene/polyaniline hydrogel enhancing skin wound healing.

Nature-inspired flexible and multifunctional hydrogels are ideal materials for tissue repair. High-strength, wear-resistant, antibacterial and conductive hydrogels can potentially be applied in skin healing. However, their use is often hindered by problems including poor mechanical properties and conductivity. Herein, high-strength and conductivity and antibacterial polyvinyl alcohol (PVA) hydrogels with Ti3C2Tx (MXene) and polyaniline (PANI) have been developed to enhance skin wound healing. MXene strengthens the hydrogen bonds between PVA molecules and provides antibacterial ability lighted by near-infrared (NIR). PANI acts as an electric conductor and forms chemical bonds via polymerization with PVA to further enhance the mechanical properties of hydrogels. The PVA/MXene/PANI (PMP) hydrogels exhibit excellent mechanical properties (with a tensile strength of 4.1 MPa and a fracture energy of 130 kJ m-2), high electrical conductivity (0.22 S m-1) and antibacterial ability. The hydrogels significantly inhibit bacterial activity in vitro and vivo. Meanwhile, the hydrogels promote proliferation and enhance the migration of cells by electrical stimulation (ES). In addition, PMP hydrogels obviously accelerate skin wound healing by promoting angiogenesis and collagen deposition. Therefore, PMP multifunctional hydrogels are a prospective wearproof material for wound-healing dressings.

Tunable Size of Hierarchically Porous Alumina Ceramics Based on DIW 3D Printing Supramolecular Gel.

A new three-dimensional (3D) printing gel is developed to construct hierarchically porous ceramics with adjustable millimeter-, micrometer-, and nanometer-scale size for application in thermal management. Not only does the gel based on supramolecular micelles exhibit excellent DIW 3D printability but also the supramolecular micelles act as templates that can precisely control the structure of micrometer-scale pores. The effect of millimeter- and µmicrometer-scale size on properties of porous ceramics is investigated in detail. The 3D-printed ceramic foam with millimeter-scale pores and smaller micrometer-scale pores shows better thermal insulation and lower compressive strength. For the thermal insulation, the local temperature of a chip exposed to contact heat is only 34.2 °C in the presence of a printed foam cap with a pore size of 41.5 µm, while the local temperature is 54.8 °C in the absence of the printed foam cap. The study provides a new method to construct hierarchically porous alumina ceramics with precisely tunable size, avoiding the issues of subtractive manufacturing and opening up new applications in portable devices or consumer electronics.

Co-MnO2 Nanorods for High-Performance Sodium/Potassium-Ion Batteries and Highly Conductive Gel-Type Supercapacitors.

Manganese dioxide (MnO2 ) is considered as a strong candidate in the field of new-generation electronic equipment. Herein, Co-MnO2 has excellent electrochemical properties in tests as the cathode electrode of sodium-ion batteries and potassium-ion batteries. The rate performance remains at 50.2 mAh g-1 at 200 mA g-1 for sodium-ion batteries. X-ray diffraction (XRD) is utilized to evaluate the crystal structure transition from Co0.2 -MnO2 to NaMnO2 with discharge to 1 V, proving that Co-doping does indeed facilitate the acceleration of ion transport and support layer spacing to stabilize the structure of MnO2 . Subsequently, highly conductive (0.0848 S cm-1 ) gel-type supercapacitors are prepared by combining Co0.2 -MnO2 , potassium hydroxide (KOH), and poly(vinyl alcohol) (PVA) together. Co0.2 -MnO2 provides capacitive behavior and strengthens the hydrogen bonds between molecules. KOH acts as an ion crosslinker to enhance hydrogen bond and as electrolyte to transport ions. 5 wt% Co0.2 -MnO2 @KOH/PVA has superb mechanical endurance, appreciable electrical conductivity, and ideal capacitive behavior. The quasi-solid-state supercapacitor demonstrates stabilized longevity (86.5% at 0.2 mA cm-3 after 500 cycles), which can greatly promote the integration of flexible energy storage fabric devices.

Biomimetic cuttlebone polyvinyl alcohol/carbon nanotubes/hydroxyapatite aerogel scaffolds enhanced bone regeneration.

Inspired by the ordered porous nanostructure of bone, biomimetic functionalization porous biomaterial could be considered as promising substitutes for bone regeneration. To realize the relevant biomimetic porous structure, polyvinyl alcohol (PVA)-based biomimetic cuttlebone aerogel scaffold which simultaneously contained modified carbon nanotubes (MCNTs) and hydroxyapatite (HAP) was first prepared using a one-step rapid freeze-drying method. By adjusting the MCNTs contents, both the surface hydrophilicity and the mechanical properties of the scaffold could be improved concurrently. Besides, the PVA/MCNTs/HAP enhanced the adhesion, differentiation and gene expression of osteogenic markers performances of MC3T3-E1 cells. Furthermore, the aerogel scaffolds were implanted into the calvarial defect model of SD IGS Rat to evaluate osteogenic performance in vivo. The Micro-CT characterization and bone content theoretical analysis after 8 weeks together indicated that the PVA/MCNTs/HAP aerogel scaffolds could accelerate bone regeneration without the contribution of endogenous cytokines. The unique biomimetic porous structure, superior mechanical properties and excellent bone regeneration capacity of PVA/MCNTs/HAP aerogel scaffolds made them potential materials for bone regeneration.

Dual Doping of Titania for Enhanced Na Storage Performance.

The sluggish sodium-ion diffusion kinetics and low electronic conductivity have severely restricted the development of the TiO2 anode for sodium-ion batteries. Defect engineering, such as single-heteroatom doping and oxygen vacancies, has proven to be effective methods to improve the conductivity of TiO2, but a comprehensive understanding of the synergistic effect of dual-heteroatom doping and oxygen vacancies on the sodium storage performance of TiO2 is still lacking. Herein, we design a synergistic strategy of dual doping via the in situ doping and hydrogenation treatment to improve conductivity and cycling stability of TiO2. Experiments and theoretical calculations together revealed that N and C doping reduces the band gap of TiO2, while the presence of oxygen vacancies efficiently accelerates the diffusion of sodium ions. Thus N, C, and oxygen vacancies with high concentration co-doped TiO2, resulting in extraordinary high-rate performance, significant stable cycling, and long-term cyclability of up to 10,000 cycles. The synthesis strategy of dual doping proposed here emphasizes the importance of defect engineering in improving material conductivity and electrode cycling stability for possible practical applications in the near future.

A superhydrophobic coating harvesting mechanical robustness, passive anti-icing and active de-icing performances.

HYPOTHESIS: Ice accretion is a challenging issue for various residential activities and industrial facilities. However, most of the current anti/de-icing coatings fail to maintain their properties when subject to frequent mechanical wear, and their limited functionality (either anti-icing or de-icing individually) cannot meet the requirement of all-weather utilization. EXPERIMENTS: Herein, a multifunctional superhydrophobic coating is prepared by compositing ferroferric oxide nanoparticles (Fe3O4 NPs) with fluorinated epoxy resin via an inverse infiltration process. The surface composition, morphology and wettability are systematically characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), laser scanning microscopy and contact angle tensiometer. The anti-icing and de-icing performances are evaluated by investigating the freezing delay and photothermal effect, respectively. FINDINGS: This coating shows outstanding water repellency (water contact angle up to 161.0°, sliding angle down to 1.4°) and can maintain superhydrophobicity within 400 cycles of tape peeling, 260 cycles of sandpaper abrasion or 25 cycles of sand impact. Besides, because the hydrophobic nano/micro hierarchical structures tremendously retard the heat transfer, the freezing process of water droplet on this coating can be apparently delayed by up to 35 min as compared to the uncoated substrate. Moreover, owing to the photothermal effect of the Fe3O4 NPs, the coating's surface temperature can be rapidly increased above 0 °C under infrared irradiation, which facilitates the ice melting on cold surfaces. Our work offers a versatile approach to address the icing problems in diverse weather conditions, which exhibits great prospects in various engineering applications.

Simultaneously Improved Thermal and Dielectric Performance of Epoxy Composites Containing Ti3C2Tx Platelet Fillers.

Polymer composites with enhanced thermal and dielectric properties can be widely used in electric and energy related applications. In this work, epoxy composites have been prepared with Ti3C2Tx, one of the most studied MXene materials that can be massively produced by direct etching using hydrofluoric acid. The addition of conductive two dimensional Ti3C2Tx platelet fillers leads to improved but anisotropic thermal conductivity of the composites. The through-plane thermal conductivity reaches 0.583 Wm-1K-1 and the in-plane thermal conductivity reaches 1.29 Wm-1K-1 when filler content is 40 wt% (21.3 vol%), achieving enhancements of 2.92 times and 10.65 times respectively, as compared with epoxy matrix. The dielectric permittivity of epoxy composite is enhanced by a factor of ~2.25 with 40 wt% fillers, and the dielectric losses are within a small value of 0.02. The results prove the effectiveness of Ti3C2Tx in simultaneously improving thermal and dielectric performance of epoxy composites, and it is deduced that further improvements may be obtained by using Ti3C2Tx nanoflake fillers.

Hierarchical Ti3C2Tx MXene/Ni Chain/ZnO Array Hybrid Nanostructures on Cotton Fabric for Durable Self-Cleaning and Enhanced Microwave Absorption.

The increasing demand for wearable electronics and the intensification of electromagnetic pollution have boosted the exploration of high-performance flexible microwave absorption (MA) materials. Herein, the hierarchical Ti3C2Tx MXene/Ni chain/ZnO array hybrid nanostructures are rationally constructed on cotton fabric for acquiring enhanced MA performance and durable self-cleaning ability. Based on the high dielectric loss capacity of MXenes and ZnO arrays, by controlling dip-coating numbers of Ni chains, the magnetic loss can be manipulated to modulate the impedance matching, reflection loss (RL), and effective absorption bandwidth (EAB, the bandwidth of RL < -10 dB). The minimum RL value of the designed fabric can reach -35.1 dB at 8.3 GHz with a thickness of 2.8 mm, and its EAB can cover the whole X-band with only a 2.2 mm thickness. In addition, the designed fabric also exhibits superior liquid repellency and durable self-cleaning ability due to the combination of the hybrid nanostructures and a superhydrophobic coating. This work provides an insight for rational design of textile-based MA materials, showing potential applications in flexible and wearable functional electronics.

Porous Sb with three-dimensional Sb nanodendrites as electrode material for high-performance Li/Na-ion batteries.

The increasing demand in energy consumption and the use of clean energy from sustainable energy sources have driven the research in the development of advanced materials for Li-ion and Na-ion batteries. In this work, we have developed a simple technique to synthesize a porous Sb structure through a galvanic replacement reaction between Sb3+ and Zn particles. The porous Sb structure consists of a three-dimensional-hierarchical structure with tree-like nanoscale Sb dendrites. The Sb in the nanodendrites is crystal of a rhombohedral structure. We construct Li-/Na-ion half cells and Li-/Na-ion full cells with the Sb nanodendrites as the active material in the working electrode and anode, respectively, and introduce an additive of vinylene carbonate for the Li-ion half/full cells and an additive of fluoroethylene carbonate for the Na-ion half/full cells. All the Li-/Na-ion half cells and Li-/Na-ion full cells exhibit excellent electrochemical performance and cycling stability. Such excellent performance can be attributed to the synergistic interaction between the three-dimensional-dendritic structure and electrolyte, which likely ensures fast transport of ions and electrons and the formation of a stable solid-state interphase.

Fog Collection on a Bio-inspired Topological Alloy Net with Micro-/Nanostructures.

Because of the scarcity of freshwater resources, fog collection as one of the effective methods to solve this issue has attracted widespread concern. Inspired by several natural creatures with the capability to collect water from fog, the bio-inspired water-harvesting materials have aroused considerable attention and been widely developed. Inspired by the directional water droplets transportation to the apex on both shorebirds beaks and wheat awns, the bio-inspired topological alloy net with a V-shaped asymmetric geometry in its mesh was designed for fog collecting. Then, micro-/nano-hierarchical structures were modified on the surface of the netting wire via the cathodic electrodeposition method. Thus, the bio-inspired topological alloy net with micro/nanostructures was fabricated successfully. Through the integration of topological geometry and surface microstructure, not only the water-collection rate is improved by efficient drainage along the designated pathways, but also the issue of mesh clogging is resolved. In addition, a theoretical model was constructed to reveal the mechanism, especially the resultant force arising from the V-shaped structure. This work provides insight into the development of novel fog-collecting materials, which has potential applications in other fields, such as liquid transportation, microfluidics, and interface science.

High Temperature Mechanical Response and Failure Analysis of 3D Five-Directional Braided Composites with Different Braiding Angles.

Three-dimensional (3D) five-directional braided composites are extensively applied in aeronautics and national defense due to their integrity and structural superiorities. In this paper, 3D five-directional braided carbon/epoxy composites were manufactured, and the high temperature mechanical response and failure mechanisms of composites with braiding angles of 21° and 32° were studied. The out-of-plane compression tests of composites with different braiding angles were conducted at temperatures ranging from 25 °C to 180 °C. Then compression stress-strain curves, compression mechanical response, and failure modes of composites at high temperatures were analyzed and compared. The results show that compression stress-strain curves linearly increased at the initial stage and dropped at various degrees at different temperatures for composites with different braiding angles. The temperature and braiding angle were both important parameters affecting out-of-plane compression properties of 3D five-directional braided composites. Mechanical properties decreased with increasing temperature for both 21° and 32° specimens. Moreover, composites with a small braiding angle possessed higher properties at each temperature point. The morphologies manifested that the failures were a symmetric ±45° shear crack for 21° specimens and a thorough 45° shear crack for 32° specimens, and a 45° fracture weakened with increasing temperature.

Mechanical and anticorrosive properties of graphene/epoxy resin composites coating prepared by in-situ method.

The graphene nanosheets-based epoxy resin coating (0, 0.1, 0.4 and 0.7 wt %) was prepared by a situ-synthesis method. The effect of polyvinylpyrrolidone/reduced graphene oxide (PVP-rGO) on mechanical and thermal properties of epoxy resin coating was investigated using nanoindentation technique and thermogravimetric analysis, respectively. A significant enhancement (ca. 213% and 73 °C) in the Young modulus and thermal stability of epoxy resin coating was obtained at a loading of 0.7 wt %, respectively. Furthermore, the erosion resistance of graphene nanosheets-based epoxy resin coating was investigated by electrochemical measurement. The results showed also that the Rrcco (ca. 0.3 mm/year) of graphene nanosheets-based epoxy resin coating was far lower than neat epoxy resin (1.3 mm/year). Thus, this approach provides a novel route for improving erosion resistance and mechanical-thermal stability of polymers coating, which is expected to be used in mechanical-thermal-corrosion coupling environments.