Hexagonal boron nitride (hBN) is a structural analog of graphene, with unique mechanical, thermal, and optical properties that make it desirable for a variety of applications. Production of stable dispersions of well-exfoliated hBN nanosheets, particularly in a nontoxic and inexpensive way, is an important step in the production of hBN macromaterials on an industrial scale. Here, we investigate the use of surfactants for exfoliating and dispersing hBN in aqueous solution. Dispersions in nine different surfactants and water were compared based on dispersion yield, quality, and stability. It was revealed that at low centrifugal force, large-molecular-weight nonionic surfactants disperse the most material. In contrast, when stronger centrifugation is applied, all surfactants produce similar dispersion yields, with dispersions in ionic surfactants containing significantly more exfoliated nanosheets and remaining stable over much longer periods of time. Finally, to demonstrate the scalability and effectiveness of these systems for making macroscopic materials, a dispersion of hBN in sodium dodecyl sulfate (SDS) was used to produce a transparent hBN film that can be deposited on glass and potentially used as an antibacterial or thermally resistant coating.

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter-sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high-performance applications.

Chlorosulfonic acid and oleum are ideal solvents for enabling the transformation of disordered carbon nanotubes (CNTs) into precise and highly functional morphologies. Currently, processing these solvents using extrusion techniques presents complications due to chemical compatibility, which constrain equipment and substrate material options. Here, we present a novel acid solvent system based on methanesulfonic or p -toluenesulfonic acids with low corrosivity, which form true solutions of CNTs at concentrations as high as 10 g/liter (≈0.7 volume %). The versatility of this solvent system is demonstrated by drop-in application to conventional manufacturing processes such as slot die coating, solution spinning continuous fibers, and 3D printing aerogels. Through continuous slot coating, we achieve state-of-the-art optoelectronic performance (83.6 %T and 14 ohm/sq) at industrially relevant production speeds. This work establishes practical and efficient means for scalable processing of CNT into advanced materials with properties suitable for a wide range of applications.

Hexagonal boron nitride (h-BN), also known as white graphene, presents an unparalleled combination of properties, including superior mechanical strength, good thermal conductivity, a wide band gap, and chemical and thermal inertness. However, because of its aversion to chemical modification, its applications have not progressed as much as those of carbon nanomaterials. In this manuscript, we show the functionalization of hexagonal boron nitride using alkyl halides in strongly reducing conditions (Billups–Birch conditions). The tunability of the Billups–Birch reaction is demonstrated by alkylating hexagonal boron nitride with 1-bromododecane and varying equivalents of Li to BN. We found that using a 1:20 BN/Li ratio yields the highest chemical modification, as demonstrated using thermogravimetric analysis and Fourier transform infrared spectroscopy, and supported by X-ray photoelectron spectroscopy. Imaging of the functionalized h-BN (fh-BN) revealed that its sheets exfoliate better in isopropanol than pristine h-BN, which displays highly stacked nanostructures. Moreover, bearing alkyl chains confers the nanosheets with improved dispersibility in nonpolar solvents, such as dodecane, and allows the formation of hydrophobic films.

No abstract