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

Na Wu,Daxin Han,Zhihui Zeng,Nico Kummer,Gustav Nyström,Renato Zenobi

doi:10.1002/smtd.202100889

Abstract

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 (≈1.4nm) 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 0.9µm and exhibit a high SE of 33.3dB, which cannot be achieved by pure MXene films. This leads to ultrahigh thickness-specific SE and surface-specific SE values of 37000dBmm-1 and 148000dBcm2 g-1 respectively, significantly surpassing those of previously reported MXene-based films.

Highlights

Electromagnetic interference (EMI) shielding materials Compared to solid copper or stainless steel with SSE values are gaining importance because of the urgent need for of around 30 dB cm2 g−1,[9] MXene-based films show great
Some Cellulose nanofibers (CNFs)-reinforced MXene films prepared in the vacuum filtration approach showed considerable EMI shielding effectiveness (SE) at thicknesses of only tens of micrometers,[23] significantly compromised electrical conductivity and EMI shielding performance still existed
The SEA is dominant in the EMI shielding performance, which is similar to that of other reported MXene-based shielding architectures.[8,23a,c] Combined with the maintained high electrical conductivity contributing to a slightly reduced shielding by reflection (SER) for MXene/CNF composites with 30 wt% CNF, slightly higher SET values were achieved for physically cross-linked MXene (P-MXene) and PC-MXene films

Summary

Introduction

SE (SSE),[1b,8] defined as the SE divided by the thickness and density of shields, of 25 863 dB cm g−1 for the MXene films. Cellulose nanofibers (CNFs),[20] made from the most abundant polymer on earth, can show diameters of a few to tens of nanometers, which is promising for minimizing the insulating gaps between conductive nanomaterials and a high electrical conductivity can be obtained.[21] With their good gelation capability, excellent mechanical strength, and large aspect ratios, CNFs can act as sustainable, biodegradable nanoscale binders of various nanomaterials, leading to an efficient construction of robust CNF-based EMI shields.[22] some CNF-reinforced MXene films prepared in the vacuum filtration approach showed considerable EMI SE at thicknesses of only tens of micrometers,[23] significantly compromised electrical conductivity and EMI shielding performance still existed. This work suggests a convenient, facile, low-cost, and scalable preparation approach for constructing high-performance MXene macrostructures with potential applications in next-generation flexible electronic devices and aerospace

Results and Discussion

Conclusions

Experimental Section

Data Availability Statement