Simultaneous exfoliation and functionalization of large-sized boron nitride nanosheets for enhanced thermal conductivity of polymer composite film

Abstract

Hexagonal boron nitride nanosheets (BNNS) are of considerable interest as building fillers to hybridize with other organic components to create thermal conductive frameworks. However, it is still a challenge to prepare functionalized BNNS with high aspect ratio and good dispersibility. Here, a unique method based on temperature pretreatment and glucose-assisted mechanical agitation is developed to achieve a high actual exfoliation yield (47%) of BNNS with high aspect ratio and few lattice defects. The resultant BNNS are covalently grafted with hydroxyl groups and well dispersed in water for storage. Density functional theory investigation and experimental work are carried out to illustrate the mechanism of exfoliation and functionalization of hexagonal boron nitride (h-BN). The high contact area of the adjoined high aspect ratio nanosheets easily causes less phonon scattering and more payload transfer. Accordingly, at the BNNS loading of 20 wt%, the BNNS/polyvinyl alcohol (PVA)/chitosan (CS) film presents a high thermal conductivity of 38.21 W m−1 K−1 in the in-plane direction and excellent tensile strength of 128.3 MPa. In addition, this new scalable exfoliation strategy can be motivating for fabricating other two-dimensional materials including graphene, tungsten disulfide (WS2), and molybdenum disulfide (MoS2).