Efficient exfoliation and functionalization of hexagonal boron nitride using recyclable ionic liquid crystal for thermal management applications

Due to their high thermal conductivity, hexagonal boron nitride nanosheets (BNNS) have great promise for thermal management materials. However, the lack of efficient, low cost, and large-scale approach to prepare functionalized BNNS is still the main factor limiting this research so far. Here, an ionic liquid crystal (ILC)-assisted method based on mechanical exfoliation is proposed to prepare functionalized BNNS. Importantly, free ILC can be recycled after exfoliation, thus reducing costs and expanding production. This method demonstrates that BNNS could still be prepared from ILC after nine times of recycling and reuse and the chemical structure of ILC was not destroyed. The reliable interaction between BNNS and ILC would achieve the noncovalent functionalization of BNNS. The resulting functionalized BNNS exhibited remarkable dispersion stability in water and organic liquids. Thanks to the excellent comprehensive properties of the functionalized BNNS, multifunctional flexible BNNS/aramid nanofibers (ANFs) composite papers is prepared. Compared to pure ANF papers, the BNNS/ANF composite papers have a significantly improved mechanical properties, thermal conductivity, flame retardance, and acid-base resistance. The ILC recycling approach has proved to be efficient, low cost, and green, providing a practical route to expedite its application for thermal management in modern electronic devices.