Sandwich-structural Ni/Fe3O4/Ni/cellulose paper with a honeycomb surface for improved absorption performance of electromagnetic interference

Cellulose-Based Electromagnetic Functional Aerogels: Mechanism, Fabrication, Structural Design, and Application

Electromagnetic functional materials offer a promising solution to reduce impacts from electromagnetic pollution and interference, such as digital communications, national defenses, and military fields. Cellulose-based aerogels, featured with their hierarchical porous structure, high specific surface area, and surface activity, can be engineered to possess electromagnetic wave shielding and absorption capabilities through structural regulation, composition optimization, and material functionalization. Moreover, these cellulose-based aerogels exhibit remarkable renewability and biocompatibility, highlighting their significant potential in the field of electromagnetic functional materials. In this review, we stigmatically overview the state-of-the-art of cellulosic electromagnetic functional aerogels, which begins with elucidating the mechanisms behind electromagnetic interference shielding and microwave absorption. The material design based on the physical and chemical characteristics of cellulose aerogels is discussed. Furthermore, the hierarchical design strategies of the cellulosic electromagnetic functional aerogels are reviewed including macro-structures, micro/nanostructures, and supramolecular structures. Multifunctional applications of cellulose electromagnetic functional aerogels are presented, such as infrared and radar stealth materials, intelligent responsive electromagnetic devices, and radiation protection equipment. Finally, an up-to-date summary and an outlook on developing the cellulose-based electromagnetic functional aerogels are provided in the fields of electromagnetic interference shielding and microwave absorption, as well as outlining future research perspectives.

Ultra-Low Loading of Ultra-Small Fe3 O4 Nanoparticles on Nonmodified CNTs to Improve Green EMI Shielding Capability of Rubber Composites

From a material design perspective, the incorporation of Fe3 O4 @carbon nanotube (Fe3 O4 @CNT) hybrids is an effective approach for reconciling the contradictions of high shielding and low reflection coefficients, enabling the fabrication of green shielding materials and reducing the secondary electromagnetic wave pollution. However, the installation of Fe3 O4 nanoparticles on nonmodified and nondestructive CNT walls remains a formidable challenge. Herein, a novel strategy for fabricating the above-mentioned Fe3 O4 @CNTs and subsequently assembling segregated Fe3 O4 @CNT networks in natural rubber (NR) matrices is proposed. The advanced and unique structure, magnetism, and lossless conductivity endow the as-obtained Fe3 O4 @CNT/NR with a shielding effectiveness (SE) of 63.8 dB and a low reflection coefficient of 0.24, which indicates a prominent green-shielding capability that surpasses those of previously reported green-shielding materials. Moreover, the specific SE reaches 531 dB cm-1 , exceeding that of those of previously reported carbon/polymer composites. Meanwhile, the outstanding conductivity enables the composite to reach a saturation temperature of ≈95 °C at a driving voltage of 1.5 V with long-term stability. Therefore, the as-fabricated Fe3 O4 @CNT/rubber composites represent an important development in green-shielding materials that are applied in cold environment.

Surfactant-Mediated Highly Conductive Cellulosic Inks for High-Resolution 3D Printing of Robust and Structured Electromagnetic Interference Shielding Aerogels

Technological fusion of emerging three-dimensional (3D) printing of aerogels with gel processing enables the fabrication of lightweight and functional materials for diverse applications. However, 3D-printed constructs via direct ink writing for fabricating electrically conductive structured biobased aerogels suffer several limitations, including poor electrical conductivity, inferior mechanical strength, and low printing resolution. This work addresses these limitations via molecular engineering of conductive hydrogels. The hydrogel inks, namely, CNC/PEDOT-DBSA, featured a unique formulation containing well-dispersed cellulose nanocrystal decorated by a poly(3,4-ethylene dioxythiophene) (PEDOT) domain combined with dodecylbenzene sulfonic acid (DBSA). The rheological properties were precisely engineered by manipulating the solid content and the intermolecular interactions among the constituents, resulting in 3D-printed structures with excellent resolution. More importantly, the resultant aerogels following freeze-drying exhibited a high electrical conductivity (110 ± 12 S m-1), outstanding mechanical properties (Young's modulus of 6.98 MPa), and fire-resistance properties. These robust aerogels were employed to address pressing global concerns about electromagnetic pollution with a specific shielding effectiveness of 4983.4 dB cm2 g-1. Importantly, it was shown that the shielding mechanism of the 3D printed aerogels could be manipulated by their geometrical features, unraveling the undeniable role of additive manufacturing in materials design.

Liquid metal coated copper micro-particles to construct core-shell structure and multiple heterojunctions for high-efficiency microwave absorption

Facing the inherent defects of magnetic materials, the research of non-magnetic absorbers has gradually become a new direction in the research of microwave absorbers to fit the requirements of a new generation for high strength, wide effective absorption bandwidth. Herein, the liquid metal and copper (LC) composite micro-particles with multiple heterojunctions and core-shell structure, which have an excellent performance of microwave absorption (MA), were prepared by simply coating liquid metal on copper and then annealing. These special LC composite micro-particles exhibit excellent MA performance with the optimal reflection loss of -39.6 dB at thickness of 2.1 mm and a maximum effective absorption bandwidth of 4.96 GHz at thickness of 2.5 mm. The high MA performance of the LC composite particles are due to the enhancement of dielectric loss, including dipolar, interfacial, and dielectric polarization, which is caused by the special core-shell structure, multiple interfaces and heterojunctions. Furthermore, the multiple reflection/scattering of microwaves among particles or on the surface of particles also benefit to the high MA performance. Therefore, this study provides a facile method to construct multiple metal heterojunctions which have great prospects in microwave absorption applications.