Few-Layer Hydroxyl-Functionalized Boron Nitride Nanosheets for Nanoscale Thermal Management

Boron nitride nanosheets (BNNSs) are widely used as fillers to increase the thermal conductivity of a substrate. However, the solvent resistance of BNNSs limits their widespread application. In this paper, hydroxyl functionalized boron nitride nanosheets (OH-BNNSs) were prepared through a one-step aqueous shear exfoliation process. The dangling bonds were formed during the exfoliation process and were attacked by water molecules, and thereby hydroxyl functionalization of BNNSs was achieved. The OH-BNNSs were added to poly(vinyl alcohol) (PVA) to prepare a nanocomposite with high thermal conductivity. The high-speed dispersive homogenizer was selected as the shear-exfoliating device, water as solvent, and sodium dodecyl sulfate (SDS) as surfactant. The effects of operating conditions on the concentration of few-layer OH-BNNSs were systematically studied. Under the optimized conditions, 0.88 mg/mL of OH-BNNSs was obtained. The as-obtained OH-BNNSs were filled in PVA to obtain composite film. The in-plane thermal diffusivity of OH-BNNSs-PVA films reached 9.03 mm2/s, which was 40-times the in-plane thermal diffusivity of the pure PVA film and 1.6-times the in-plane thermal diffusivity of the PVA composites filled by BNNSs prepared from ultrasonic exfoliation. The reasons were attributed to better dispersibility in PVA aqueous solution for OH-BNNSs. This paper provided a simple, scalable, and environmentally friendly preparation method for OH-BNNSs.