Quantifying the Solubility of Boron Nitride Nanotubes and Sheets with Static Light Scattering and Refractometry

The dissolution of nanoparticles, particularly those containing boron, is an important area of interest for polymer nanocomposite formation and material development. In this work, the solubility of boron nitride nanotubes (BNNT), functionalized boron nitride nanotubes (FBNNT), and boron nitride sheets (BN-ZG) is quantified in toluene and THF with static light scattering, refractometry, UV-vis spectroscopy, and physical observations. UV-vis spectroscopy provides a method to determine the concentration and solubility limits of the solutions tested. Using light scattering, the second virial coefficient, A(2), is determined and used to calculate chi, the solute-solvent interaction parameter. The Hildebrand solubility parameter, delta, is then extracted from this data using the Hildebrand-Scatchard Solution Theory. A list of potential good solvents based on the estimated delta value is provided for each nanoparticle. Single-walled carbon nanotubes (SWNTs) and prepolymers (EN4 and EN8) used to synthesize polyurethanes were also tested, because the published delta and molar attraction constants of these materials provided a self-consistent check. The dn/dc of SWNTs and boron-containing particles was measured for the first time in this work. A solvent screen for BN-ZG provides additional information that supports the obtained delta and chi. Three systems were found to have chi values below 0.5 and were thermodynamically soluble: BNNT in THF, EN8 in THF, and EN8 in toluene.