On-Demand Exfoliation of Boron Nitride Nanosheets for Dielectric Polymer Nanocomposites

Boron nitride nanosheets (BNNSs) have gained extensive attention for nanodielectrics because of their large band gap and ultra-high thermal conductivity. Generally, different electrical applications require different sizes BNNSs. Although sonication-assisted liquid-phase exfoliation (SALPE), the commonly used method, can exfoliate BNNSs from bulk hexagonal boron nitride (h-BN) flakes effectively, how to regulate the BNNSs size during SALPE still lack exploration. Herein, based on SALPE, we systematically study the parameters (size of the raw materials, frequency, and power of the ultrasonic source) of BNNSs exfoliation. Then, the exfoliated BNNSs with different sizes were introduced to the polymer matrix. BNNSs with specific sizes among
$0.3-5 \mu \mathrm{m}$
were exfoliated, aiming for different applications. As an example, BNNSs with larger sizes and smaller thicknesses were used to fabricate dielectric nanocomposites with high thermal conductivity
$(3.9\ \text{Wm}^{-1}\mathrm{K}^{-1})$
and breakdown strength
$(171\ \text{kV mm}^{-1})$
for thermally conductive insulating materials. This work advances our understanding of SALPE and provides an innovative way for exfoliating BNNSs with different sizes for specific applications.