Bidirectional, Multilayer MXene/Polyimide Aerogels for Ultra-Broadband Microwave Absorption.

To obtain high-performance electromagnetic microwave (EM) absorption materials with broad effective absorption bandwidth (EAB) and reduced thickness, designing structures has proved to be a promising way. Herein, ultra-broadband multilayer bidirectional MXene/polyimide EM absorption aerogels containing multi-structures on scales ranging from the micro- to the macroscale are produced with the aid of electric and temperature fields. On the microscale, under the action of electric force and temperature gradient, the ordered structures made of aligned Ti3C2Tx MXene nanosheets and the microscale layered aerogel walls enable the bidirectional aerogel to achieve a wide EAB of 8.58 GHz at a thickness of 2.1 mm. This is ascribed to the numerous aligned nanosheets and layered aerogel walls perpendicular to the incident EMs, facilitating the conversion of electromagnetic energy into electrical energy. Furthermore, on the macroscale, the multilayer bidirectional aerogel with non-gradient structures effectively resolves the conflict between impedance matching and energy loss, resulting in an ultrawide EAB of 9.41 GHz at a thickness of 3 mm. This innovative design of electric-field-assisted multilayer bidirectional aerogels with multiscale structural coupling may provide feasible and effective pathways for the development of advanced EM absorption materials.

Constructing a Porous Structure on the Carbon Fiber Surface for Simultaneously Strengthening and Toughening the Interface of Composites.

The demand for both strength and toughness is perpetual in fiber-reinforced composites. Unfortunately, both properties are often mutually exclusive. As the mechanical properties of the composites are highly dependent on their interfacial properties, engineering interfaces between the fiber and matrix would be vital to overcome the conflict between strength and toughness. Herein, inspired by the physical interfacial architecture of grassroots-reinforced soil composites, a porous carbon nanotube-Mg(OH)2/MgO hybrid structure was constructed on the fiber surface via water electrolysis reaction and electrophoretic deposition process. The effects of the porous structure on the fiber filaments' mechanical properties, as well as the thickness on the interfacial properties, were all investigated. The results showed that fully covered porous structures on the fiber surface slightly enhanced the reliability of a single fiber in terms of mechanical properties by bridging the surface defects on the fiber. The interfacial shear strength and toughness of the porous structure-coated fiber/resin composite reached up to 92.3 MPa and 121.2 J/m2, respectively. These values were 61.30 and 121.98% higher than those of pristine fiber/resin composites, respectively. The strengthening effect was ascribed to the synergistic effects that improved numerous interfacial bonding areas and mechanical interlocking morphologies. The toughening mechanism was related to crack deflection, microcrack generation, and fracture of the porous structure during interfacial failure. Additional numerical studies by finite element analysis further proved the enhancement mechanism. Overall, the proposed method looks promising for producing advanced carbon fiber-reinforced polymer composites with excellent strength and toughness.