High-quality boron nitride nanosheets via polymer anchoring and thin-layer confined shearing exfoliationOA

Flexible,lightweight,and electrically insulated materials with high thermal conductivity and good mechanical performance are highly required for next-generation electronic devices.Hexagonal boron nitride nanosheet(BNNS)has a great potential to meet these requirements because of its high thermal conductivity,intrinsic insulation,and superior stability.However,the production of solution-processing,high quality BNNSs with larger lateral size is still challenged.Herein,we develop a thinlayer confined shearing and polymer-anchoring strategy for the exfoliation of hexagonal boron nitride(h-BN)into BNNSs.Upon optimization of the rotation speed of milling tools,chemical structure of anchored polymer,the layer thickness and rheological properties of liquid medium,the shearing force applied on h-BN crystals increases greatly.The anchored polymer(sodium carboxymethyl cellulose,CMC)can effectively promote shearing force transfer and impact buffer onto the h-BN crystals,consequently improving the exfoliation yield(84.6%)and giving BNNSs with large lateral size(1.97±1.09μm)and high aspect ratio(~746).The anchored polymer endows BNNSs with good hydrophilicity and solution processability.The BNNS(78 wt.%)/CMC film prepared by spatially confined evaporation has densely packed structure,exhibiting high tensile strength(289±21 MPa)and high in-plane thermal conductivity(59.5±2.7 W·m^(−1)·K^(−1)).Electrically-insulating yet highly thermally conducting nature enables BNNS films attractive in insulated thermal management applications.