Large-area hexagonal boron nitride nanosheets exfoliated by sodium alginate/Ca2+ assisted ball-milling and their thermal conduction rules in composite films

We discovered that incorporating the Ca 2+ into sodium alginate (SA) solution as ball-milling medium of hexagonal boron nitride ( h -BN) could increase the lateral size of the exfoliated h -BN nanosheets (BNNSs) at least twice those of pure SA solution obtained, which can be owing to the Ca 2+ −induced crosslinking of SA and enhancement of interfacial adhesion forces between SA and h -BN that not only boost the impacting resistance to milling balls but also the exfoliation energy to h -BN. Based on the crucial role of Ca 2+ in h -BN exfoliation, the large-area and small-thickness BNNSs are produced simultaneously with the increased milling speed and Ca 2+ concentration, which can be assembled into highly compact and horizontal oriented structures with aramid nanofibers (ANFs) due to the favorable compatibility, dispersity, and interfacial binding force. This kind of compact and ordered structure enables ANF/BNNS film with high thermal conductivity (TC) since the connective and high-efficiency heat conduction paths, of which the highest TC is 27.57 W⋅m −1 ⋅K -1 . Compared with soft and molecular SA chains, the ANFs show an incredible ability to guide the horizontal orientation of BNNSs for the superior TCs of their composites.