Charge Dynamics Engineering Sparks Hetero-Interfacial Polarization for an Ultra-Efficient Microwave Absorber with Mechanical Robustness.

Microwave absorbers with high efficiency and mechanical robustness are urgently desired to cope with more complex and harsh application scenarios. However, manipulating the trade-off between microwave absorption performance and mechanical properties is seldom realized in microwave absorbers. Here, a chemistry-tailored charge dynamic engineering strategy is proposed for sparking hetero-interfacial polarization and thus coordinating microwave attenuation ability with the interfacial bonding, endowing polymer-based composites with microwave absorption efficiency and mechanical toughness. The absorber designed by this new conceptual approach exhibits remarkable Ku-band microwave absorption efficiency (-55.3 dB at a thickness of 1.5 mm) and satisfactory effective absorption bandwidth (5.0 GHz) as well as desirable interfacial shear strength (97.5 MPa). The calculated differential charge density depicts the uneven distribution of space charge and the intense hetero-interfacial polarization, clarifying the structure-performance relationship from a theoretical perspective. This work breaks through traditional single performance-oriented design methods and ushers a new direction for next-generation microwave absorbers.

Integrating Multi-Heterointerfaces in a 1D@2D@1D Hierarchical Structure via Autocatalytic Pyrolysis for Ultra-Efficient Microwave Absorption Performance.

Developing microwave absorption (MA) materials with ultrahigh efficiency and facile preparation method remains a challenge. Herein, a superior 1D@2D@1D hierarchical structure integrated with multi-heterointerfaces via self-assembly and an autocatalytic pyrolysis is designed to fully unlock the microwave attenuation potential of materials, realizing ultra-efficient MA performance. By precisely regulating the morphology of the metal organic framework precursor toward improved impedance matching and intelligently integrating multi-heterointerfaces to boosted dielectric polarization, the specific return loss value of composites can be effectively tuned and optimized to -1002 dB at a very thin thickness of 1.8 mm. These encouraging achievements shed fresh insights into the precise design of ultra-efficient MA materials.

In situ interfacial evaluation of aramid/epoxy composites by interfacial stress transfer characteristics.

Interfacial bonding between aramid fibers and epoxy resin is crucial for the mechanical properties of fiber-reinforced epoxy composites. Interfacial stress transfer between resin and fibers bridges microscopic and macroscopic properties. Using micro-Raman spectroscopy for in situ stress measurement offers insights into interface bonding through assessment of interfacial stress transfer characteristics. This study measures stress distribution on loaded microdroplet sample surfaces, analyzes stress transfer at the interface, and proposes an evaluation method using finite element analysis (FEA). The results show that interfacial stress along the fiber decreases from the droplet's edge to center, indicating stress transfer between the fiber and matrix, as evidenced by the stress-dependent Raman shift of aramid fiber. The interface modulus (Eif), derived from the FEA model, effectively reflects interface bonding, with droplet shape influence removed in evaluations. The agreement between the proposed method and the transverse fiber bundle test confirms its applicability. The method offers a direct, non-destructive, and shape-independent way to evaluate the interface of aramid/epoxy composites.

Intrinsically reactive hyperbranched interface governs graphene oxide dispersion and crosslinking in epoxy for enhanced flame retardancy.

Enhancing the flame retardancy of epoxy (EP) resins typically entailed a trade-off with other physical properties. Herein, hyperbranched poly(amidoamine) (HPAA) and phytic acid (PA) were used to functionalize graphene oxide (GO) via electrostatic self-assembly in water to prepare a phosphorus-nitrogen functionalized graphene oxide nanosheet (PN-GOs), which could be utilized as high efficient flame-retardant additive of epoxy resin without sacrificing other properties. The PN-GOs demonstrated improved dispersion and compatibility within the EP matrix, which resulted in significant concurrent enhancements in both the mechanical performance and flame-retardant properties of the PN-GOs/EP nanocomposites over virgin EP. Notably, the incorporation of just 1.0 wt% PN-GOs yielded a 20.4, 6.4 and 42.7 % increases in flexural strength, flexural modulus and impact strength for the PN-GOs/EP nanocomposites, respectively. Furthermore, simultaneous reductions were achieved in the peak heat release rate (pHRR) by 60.0 %, total smoke production (TSP) by 43.0 %, peak CO production rate (pCOP) by 57.9 %, and peak CO2 production rate (pCO2P) by 63.9 %. This study presented a facile method for the design of GO-based nano flame retardants, expanding their application potential in polymer-matrix composites.

The orientation and inhomogeneous distribution of carbon nanofibers and distinctive internal structure in polymer composites induced by 3D-printing enabling electromagnetic shielding regulation.

Carbon nanofiber (CNF)/polycaprolactone (PCL) composites were three-dimention (3D) printed into electromagnetic interference (EMI) shielding parts. 3D-printing process led to an inhomogeneous CNFs distribution in printed composites. The special high-resistance "internal surfaces" introduced between printed threads reduced the conductivity of printed parts and resulted in characteristic secondary percolation phenomena. Meanwhile, the accelerated melt flow in nozzle oriented CNFs in composites along the printing direction, increasing the percolation threshold compared to the random arrangement. As two stage of percolation networks formed, the 3D-printed CNF/PCL parts exhibited excellent EMI shielding performance, with EMI shielding effectiveness value up to 58.7 dB. By controlling the packing density of the printed part, a large number of apertures and heterogeneous interfaces were easily introduced into the interior of parts. It promoted multiple reflection and absorption of electromagnetic waves inside the parts, and enabled adjustment of weight and shielding effectiveness. Therefore, the 3D printing enabled the flexible formation of complex porous structures. From basic materials to designed components, the 3D printing technology can facilitate the transformation of shielding materials into high performance components that are finely designed both internally and externally, making it a promising technology in the field of manufacturing lightweight, high performance EMI shielding materials.

Mo2C-Embedded Carambola-like N,S-Rich Carbon Framework as the Interlayer Material for High-Rate Lithium-Sulfur Batteries in a Wide Temperature Range.

The insulating nature of sulfur/Li2S and heavy shuttle effect of lithium polysulfides (LiPSs) hinder the commercialization of lithium-sulfur (Li-S) batteries. To address such issues, we designed and synthesized a porous carambola-like N,S-doped carbon framework embedded with Mo2C particles (designed as N,S-Mo2C/C-ACF) as the interlayer material to block the polysulfide shuttle and it behaves as a catalytic mediator for LiPS conversion. The modified separator of polypropylene functionalized by N,S-Mo2C/C-ACF, showing ultrafast wetting ability to the electrolyte and high lithium ion (Li+) conductivity, proves to be highly effective for inhibiting the polysulfide shuttle and simultaneously promoting the reutilization of adsorbed LiPSs. When used in Li-S batteries by coupling with a Super P/sulfur cathode, over a wide temperature range of 5-55 °C, the as-fabricated batteries delivered excellent rate capability and long cycle stability. Especially, at a high rate of 5 C, the discharge capacities of 405, 630, and 670 mA h gs-1 were achieved when tested at 5, 30, and 55 °C, respectively. The remarkable wide temperature performance is appealing for extended practical application of Li-S batteries.