Sn Whiskers from Ti2 SnC Max Phase: Bridging Dual-Functionality in Electromagnetic Attenuation.

In the ever-evolving landscape of complex electromagnetic (EM) environments, the demand for EM-attenuating materials with multiple functionalities has grown. 1D metals, known for their high conductivity and ability to form networks that facilitate electron migration, stand out as promising candidates for EM attenuation. Presently, they find primary use in electromagnetic interference (EMI) shielding, but achieving a dual-purpose application for EMI shielding and microwave absorption (MA) remains a challenge. In this context, Sn whiskers derived from the Ti2 SnC MAX phase exhibit exceptional EMI shielding and MA properties. A minimum reflection loss of -44.82 dB is achievable at lower loading ratios, while higher loading ratios yield efficient EMI shielding effectiveness of 42.78 dB. These qualities result from a delicate balance between impedance matching and EM energy attenuation via adjustable conductive networks; and the enhanced interfacial polarization effect at the cylindrical heterogeneous interface between Sn and SnO2 , visually characterized through off-axis electron holography, also contributes to the impressive performance. Considering the compositional diversity of MAX phases and the scalable fabrication approach with environmental friendliness, this study provides a valuable pathway to multifunctional EM attenuating materials based on 1D metals.

Robust and Flame-Retardant Zylon Aerogel Fibers for Wearable Thermal Insulation and Sensing in Harsh Environment.

The exceptional lightweight, highly porous, and insulating properties of aerogel fibers make them ideal for thermal insulation. However, current aerogel fibers face limitations due to their low resistance to harsh environments and a lack of intelligent responses. Herein, a universal strategy for creating polymer aerogel fibers using crosslinked nanofiber building blocks is proposed. This approach combines controlled proton absorption gelation spinning with a heat-induced crosslinking process. As a proof-of-concept, Zylon aerogel fibers that exhibited robust thermal stability (up to 650 °C), high flame retardancy (limiting oxygen index of 54.2%), and extreme chemical resistance are designed and synthesized. These fibers possess high porosity (98.6%), high breaking strength (8.6 MPa), and low thermal conductivity (0.036 W m-1 K-1 ). These aerogel fibers can be knotted or woven into textiles, utilized in harsh environments (-196-400 °C), and demonstrate sensitive self-powered sensing capabilities. This method of developing aerogel fibers expands the applications of high-performance polymer fibers and holds great potential for future applications in wearable smart protective fabrics.

Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation.

Two-dimensional transition metal carbides and nitrides (MXene) have emerged as promising candidates for microwave absorption (MA) materials. However, they also have some drawbacks, such as poor impedance matching, high self-stacking tendency, and high density. To tackle these challenges, MXene nanosheets were incorporated into polyacrylonitrile (PAN) nanofibers and subsequently assembled into a three-dimensional (3D) network structure through PAN carbonization, yielding MXene/C aerogels. The 3D network effectively extends the path of microcurrent transmission, leading to enhanced conductive loss of electromagnetic (EM) waves. Moreover, the aerogel's rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXene-based absorbers. EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss (RLmin) value of - 53.02 dB (f = 4.44 GHz, t = 3.8 mm), and an effective absorption bandwidth (EAB) of 5.3 GHz (t = 2.4 mm, 7.44-12.72 GHz). Radar cross-sectional (RCS) simulations were employed to assess the radar stealth effect of the aerogels, revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m2. In addition to the MA performance, the MXene/C aerogel also demonstrates good thermal insulation performance, and a 5-mm-thick aerogel can generate a temperature gradient of over 30 °C at 82 °C. This study provides a feasible design approach for creating lightweight, efficient, and multifunctional MXene-based MA materials.

In-Situ Growth of ZnO Whiskers on Ti2ZnC MAX Phases.

ZnO whiskers have many applications, such as in medical and photocatalysis fields. In this study, an unconventional preparation approach is reported, realizing the in-situ growth of ZnO whiskers on Ti2ZnC. The weak bonding between the layer of Ti6C-octahedron and the Zn-atom layers leads to the easy extraction of Zn atoms from Ti2ZnC lattice points, resulting in the formation of ZnO whiskers on the Ti2ZnC surface. This is the first time that ZnO whiskers have been found to grow in-situ on Ti2ZnC substrate. Further, this phenomenon is amplified when the size of the Ti2ZnC grains is mechanically reduced by ball-milling, which bodes a promising route to prepare ZnO in-situ on a large scale. Additionally, this finding can also help us better understand the stability of Ti2ZnC and the whiskering mechanism of MAX phases.

Lithium storage performance and mechanism of nano-sized Ti2InC MAX phase.

Fine powders of MAX phases (a family of layered carbides/nitrides) have been showing great promise in energy storage applications. A feasible method of obtaining nano-sized MAX phase particles is critical to realizing the practical application of the vast MAX phase family in more technologically important fields. Herein, ball milling, a commercial and feasible method, is employed to prepare nano-sized Ti2InC, which delivers a high specific capacity of 590 mA h g-1 after 500 cycles and maintains 574.4 mA h g-1 after 600 cycles at 0.1 A g-1 when used as a lithium storage anode. Compared with other methods (e.g., partial etching), decreasing the size of Ti2InC particles by ball milling can preserve the exfoliated indium (In) atoms, which have great volumetric and gravimetric capacities. In situ XRD analysis indicates that the capacity of the nano-sized Ti2InC primarily comes from the lithiation of elemental In exfoliated from Ti2InC, and in particular, the exfoliated In atoms by ball milling can increase the initial capacity. The lithiation/delithiation cycle can effectively activate and even exfoliate the Ti2InC grains, which accounts for the increasing capacity upon cycling.

Hyperelastic Kevlar Nanofiber Aerogels as Robust Thermal Switches for Smart Thermal Management.

Aerogels, the lightest artificial solid materials characterized by low density and thermal conductivity, high porosity, and large specific surface area, have attracted increasing interest. Aerogels exhibit single-mode thermal insulation properties regardless of the surrounding temperature. In this study, hyperelastic Kevlar nanofiber aerogels (HEKAs) are designed and fabricated by a slow-proton-release-modulating gelation and thermoinduced crosslinking strategy. The method does not use crosslinking agents and endows the ultralow-density (4.7 mg cm-3 ) HEKAs with low thermal conductivity (0.029 W m-1 K-1 ), high porosity (99.75%), high thermal stability (550 °C), and increased compression resilience (80%) and fatigue resistance. Proofs of the concept of the HEKAs acting as on-off thermal switches are demonstrated through experiments and simulations. The thermal switches exhibit a rapid thermal response speed of 0.73 °C s-1 , high heat flux of 2044 J m-2 s-1 , and switching ratio of 7.5. Heat dissipation can be reversibly switched on/off more than fifty times owing to the hyperelasticity and fatigue resistance of the HEKAs. This study suggests a route to fulfill the hyperelasticity of highly porous aerogels and to tailor heat flux on-demand.

Lightweight and flexible PAN@PPy/MXene films with outstanding electromagnetic interference shielding and Joule heating performance.

Lightweight and flexible multifunctional materials with excellent electromagnetic interference (EMI) shielding and Joule heating performances are highly demanded for smart and wearable electronics. In this work, polyacrylonitrile (PAN) nanofiber films are prepared by electrospinning and then coated with polypyrrole (PPy) via vapor deposition, yielding a continuous three-dimensional (3D) conductive network of PAN@PPy. Ti3C2Tx MXene nanosheets with high electrical conductivity are sprayed on the PAN@PPy film to enhance its EMI shielding performance. The as-prepared PAN@PPy/MXene films (55 µm thick) exhibit a high EMI shielding effectiveness (SE) of 32 dB, achieving an extraordinarily high normalized surface-specific SE (SSE/t) of up to 17 534.5 dB cm2 g-1 from 8.2 to 12.4 GHz; simultaneously, the temperatures of PAN@PPy/MXene films can be driven up to 170.5 °C at an input voltage of 4 V, and exhibit fast-response, stable, and long-term Joule heating performance. The high SSE/t and efficient Joule heating ability of the films bode potential applications in smart and wearable devices.