Quantifying the Thermodynamic Interactions in Carborane Nanoparticle Solutions

The dissolution of nanoparticles, particularly those containing boron, is an important area of interest for polymer nanocomposite formation and material development (1-2). In this work, the solubility of four boron cage molecules are quantified in toluene, THF, and methyl ethyl ketone 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, A2, was determined and used to calculate $\chi$, the solute-solvent interaction parameter. The Hildebrand solubility parameter, $\delta$, was then extracted from this data using the Hildebrand-Scatchard solution theory (3-4). A list of potential good solvents based on the extracted $\delta$ value is provided for each nanoparticle. Of the systems tested, 1,3-di-o-carboranylpropane was shown to be a thermodynamically stable in toluene, with a $\chi$ less than 0.5, a solubility limit of 2.47 mg/mL, and all solutions remaining clear with no visible particle settling.