Na Wu1, Zhihui Zeng2,3, Nico Kummer3,4, Daxin Han5, Renato Zenobi1, Gustav Nyström3,4
- Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
- School of Materials Science and Engineering, Shandong University, Jinan, 250061 P. R. China
- Laboratory for Cellulose and Wood Materials, Swiss Federal Laboratories for Materials Science and Technology (Empa), 8600 Dübendorf, Switzerland
- Department of Health Sciences and Technology, ETH Zürich, 8092 Zürich, Switzerland
- Department of Information Technology and Electrical Engineering, ETH Zürich, 8092 Zürich, Switzerland
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 cm2 g−1 respectively, significantly surpassing those of previously reported MXene-based films.
CovalX Technology Used
A study was conducted researchers at the ETH in Zurich, Switzerland to test for the improvement of EMI shields performance after utilizing ultrafine cellulose nanofibers to create physically and chemically cross-linked MXenes nanosheets (PC-MXenes). CovalX’s high mass MALDI-TOF/TOF mass spectrometer was used to analyze the dual cross-linking of PC-MXenes and confirm the improvement of mechanical strength, hydrophobicity, and oxidation stability while maintaining the levels of EMI shielding effectiveness (SE). Using CovalX’s MALDI equipment allowed for highly advanced analysis while keeping the complex intact.