Polymer-Guided Exfoliation, Microstructure, Thermal Conduction, and Mechanical Behaviors of Boron Nitride Nanosheets

The size and surface properties of individual nanomaterials significantly influence the microstructures and the performance of their assemblies. Herein, we demonstrated that when using polymeric solutions as ball-milling media of hexagonal boron nitride (h-BN), the molecular structures of the employed polymers would have significant influences on the lateral sizes, surface charges, and attached polymer kinds and contents of the exfoliated boron nitride nanosheets (BNNSs), which in turn determine the microstructures and thermal conductivities (TCs) of the BNNS-based films. The polymers that have high binding energies and dipole-dipole interactions with h-BN are conducive to peeling off large-area BNNSs, but those having strong hydrogen bonding interactions with h-BN can attach more molecular chains on the exfoliated BNNSs and form dense and highly horizontally oriented structures in assembled BNNS films, of which the TCs are balanced by the lateral sizes, compactness, horizontal orientation, and interfacial interactions of the nanosheets. Density functional theory simulations confirmed that the exfoliation ability of the polymers is mainly determined by their binding energies with h-BN.