Dimethyl sulfoxide dispersion of aramid nanofibers: an excellent medium for exfoliating high-quality boron nitride nanosheets towards heat spreading films with high thermal conductivity

Herein, we used dimethyl sulfoxide (DMSO) dispersion of aramid nanofibers (ANFs) as medium to exfoliate boron nitride nanosheets (BNNSs) from their bulk materials via a ball-milling route. The obtained BNNSs displayed large lateral sizes and were very clean without any contaminants. When milling under a high energy condition, many small-area nanosheets were appeared but the sample produced with high ANF concentration could still contain more large-size BNNSs. It was concluded that the DMSO is a good exfoliating medium for BNNSs due to the suitable viscosity, molecular weight, and polarity, while the introduction of ANFs can further improve the exfoliated sizes of BNNSs because of the buffering to impacting forces of milling balls. The ANF/BNNS composite exfoliated under high energy ball-milling and high ANF concentration gained the highest in-plane thermal conductivity of 27.23 W m−1 K−1 since the densified microstructure and the high dispersity, large lateral size, and high horizontal orientation of BNNSs.