Ultrafine Cellulose Nanofiber‐Assisted Physical and Chemical Cross‐Linking of MXene Sheets for Electromagnetic Interference Shielding

Abstract

electromagnetic compatibility of electronic devices and protection of biological tissue against harmful radiation. [1] High-performance EMI shields, involving high EMI shielding effectiveness (SE), low thickness and weight, good mechanical strength and flexibility, and considerable stability, are highly desirable. [2] Owing to the excellent electrical conductivity and the large aspect ratios, low-dimensional nanomaterials such as metal nanowires, [3] carbon nanotubes (CNTs), [4] graphene, [5] or transition metal carbides and nitrides (MXenes) [6] offer great potential for bottom-up construction of EMI shielding macrostructures. Among these materials, novel 2D MXene sheets, commonly known as Ti 3 C 2 T x MXenes, have attracted attention for constructing high-performance EMI shielding materials due to the metallic conductivity and the solution processability derived from their hydrophilic functional groups (F, O, and OH). [7] For instance, vacuum filtrated MXene films showed an excellent EMI SE of 68 dB at a thickness of 11 µm. [8] This resulted in an ultrahigh surface-specific SE (SSE), [1b,8] defined as the SE divided by the thickness and density of shields, of 25 863 dB cm 2 g −1 for the MXene films. Compared to solid copper or stainless steel with SSE values of around 30 dB cm 2 g −1 , [9] MXene-based films show great Transition metal carbides and nitrides (MXenes) have shown great potential for constructing thin, high-performance electromagnetic interference (EMI) shields. The challenges with these materials involve the weak interfacial interactions of MXenes, which results in inferior mechanical properties and structure of the MXene films and a conductivity/EMI shielding performance decay related to the poor MXene oxidation stability. Numerous efforts have been devoted to improving the mechanical properties or oxidation stability of the films, which always comes at the expense of EMI shielding performance. Here, ultrafine (≈1.4 nm) cellulose nanofibers are employed to achieve physical and chemical dual cross-linking of MXene (PC-MXene) nanosheets. The procedure involves drying of flexible and highly conductive PC-MXene films at ambient pressure and is energy-efficient and scalable. Compared to the MXene films, the PC-MXene films show significantly improved mechanical strength, hydrophobicity, oxidation stability, and are waterproof, without compromising the excellent EMI shielding effectiveness (SE). Moreover, the freestanding PC-MXene films reach a thickness of merely 0.9 µm and exhibit a high SE of 33.3 dB, which cannot be achieved by pure MXene films. This leads to ultrahigh thickness-specific SE and surface-specific SE values of 37 000 dB mm −1 and 148 000 dB cm 2 g −1 respectively, significantly surpassing those of previously reported MXene-based films.

Porous and Ultra-Flexible Crosslinked MXene/Polyimide Composites for Multifunctional Electromagnetic Interference Shielding

“…Furthermore, the chemical crosslinking of MXene flakes increased the water contact angle from 0° to 118° (Figs. 2 c and S4a, Video S3), which was mainly ascribed to the introduction of the hydrophobic backbone in the PMDI [ 57 ]. As displayed in FTIR curves (Figs.…”

Biomimetic Porous MXene Sediment-Based Hydrogel for High-Performance and Multifunctional Electromagnetic Interference Shielding

“…The advancement of gigahertz (GHz) band communication technologies has significantly brought convenience for humans, while it also leads to hazardous electromagnetic interference (EMI) or radiation. − To this end, high-performance, easy-manufacturing, adjustable-performance, and low-cost EMI shields are urgently desired. , Since introducing micrometer-sized pores in EMI shields can facilitate multiple reflections of incident electromagnetic waves (EMWs) and effectively improve the EMI shielding effectiveness (SE), recently cellular foams/aerogels have attracted more and more attention for preparing high-performance EMI shields. − However, compared with the bulk shields, the foam/aerogel-based shields generally suffer from fragility as well as poor flexibility . This limits the development of high-performance EMI shields demanding good mechanical toughness, flexibility, and even stretchability, which are especially desired for next-generation flexible devices.…”

“…1−4 To this end, high-performance, easymanufacturing, adjustable-performance, and low-cost EMI shields are urgently desired. 5,6 Since introducing micrometersized pores in EMI shields can facilitate multiple reflections of incident electromagnetic waves (EMWs) and effectively improve the EMI shielding effectiveness (SE), recently cellular foams/aerogels have attracted more and more attention for preparing high-performance EMI shields. 7−10 However, compared with the bulk shields, the foam/aerogel-based shields generally suffer from fragility as well as poor flexibility.…”

Hydrogel-based composites beyond the porous architectures for electromagnetic interference shielding

“…With the rapid progress in electronic equipment and wireless technology, the booming issues of electromagnetic interference (EMI) or pollution have brought about harm to electric devices and human health [1][2][3][4][5]. Therefore, employing EMI shielding materials to protect the normal operation of electronic devices and human beings from electromagnetic radiation is essential [6,7].…”