Two-Part Surfactant-Assisted Exfoliation of Hexagonal Boron Nitride Nanosheets to Obtain Highly Stable Two-Dimensional Nanomaterial Dispersions

Printable dielectric materials that exhibit high dielectric constants and low losses at high frequencies are needed for additive manufacturing of electronic devices. One promising nanomaterial for use in such systems is hexagonal boron nitride (hBN). This 2D nanomaterial is insulating due to its wide band gap and has a dielectric constant ranging from 2 to 4, making it an ideal candidate for applications including gate dielectrics, capacitors, and passivation layers in 2D nanoelectronics. However, stabilizing the dispersion of hBN nanosheets for printing applications while minimizing the reliance on toxic solvents and excessive surfactants remains a challenge. Many of the prevailing exfoliation techniques are time-consuming and resource-intensive. This work explores a two-part, surfactant-assisted mechanical exfoliation method to obtain stable hBN nanosheet dispersions from bulk hBN in a relatively short period, using ball milling followed by probe sonication. Exfoliation of hBN nanosheets assisted by various concentrations (from 0 to 1 wt %) of Triton X -100 was explored. The yield of each mixture was quantified by thermogravimetric analysis (TGA), and a maximum yield of 18.4% was achieved using 1 wt % surfactant. Colloidal stability was examined by using UV-vis spectroscopy, and solutions were found to remain stable for up to 30 days. The quality and size of the nanosheets were assessed using X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The dielectric properties of the obtained nanosheets were measured using a vector network analyzer at microwave frequencies, and the real permittivity of the nanosheets ranged from 2.1 to 3.7 with varying concentrations of surfactant used in the synthesis. Furthermore, the nanosheets were found to be insulating and to have low dielectric loss tangents ranging from 0.012 to 0.014. The two-part, surfactant-assisted mechanical exfoliation technique requires much lower processing time than sonication alone and results in highly stable dispersions. The resulting hBN nanosheets exhibited tunable real permittivity and low dielectric loss, positioning these materials as promising options for dielectric ink formulations.