Liquid Metal-Assisted High-Efficiency Exfoliation of Boron Nitride for Electrically Insulating Heat-Spreader Film

Boron nitride nanosheets (BNNSs) are regarded as promising two-dimensional materials in thermally conductive yet electrically insulating applications. Attributed to the strong interlayer lip-lip interactions in bulk hexagonal boron nitride (h-BN), high-efficiency exfoliation and scalable fabrication of BNNSs via the top-down strategies remain formidable challenges. Herein, an interesting observation is manifested that gallium-based liquid metal (LM) forming robust coordination interactions with h-BN helps reduce the lip-lip interlayer interactions and thus facilitates successful exfoliation under intense shearing force. For example, employing the ball-milling technique, the BNNS yield can increase to 41.21% with the assistance of LM at only 2 h milling time. Its exfoliation efficiency (yield/time) reaches as high as 26.72%/h, more than 2-fold that of other previously reported methods, including sonication and other ball-milling methods. Moreover, the exfoliated BNNSs are still found to be highly electrically insulating with a band gap of 4.65 eV, showing prospective potential in thermally conductive yet electrical insulating applications. As a proof of concept, a microwave-transparent heat spreader (cellulose nanofiber/BNNSs) is fabricated and verified for applications in high-frequency thermal-management fields.

Automated summary

Gallium-based liquid metal was found to reduce interlayer interactions in boron nitride nanosheets (BNNSs), leading to high exfoliation efficiency. The exfoliated BNNSs still maintained electrical insulating properties, showing potential in thermally conductive yet electrically insulating applications.