Determination of the Hansen solubility parameters of carbon nano-onions and prediction of their dispersibility in organic solvents

Abstract

Carbon nano-onions (CNOs) are the least studied allotropes of carbon despite their discovery before nanotubes and fullerenes. CNOs are multilayered fullerenes concentrically arranged one inside the other resembling the structure of an onion. Typically, their size average ranges from 2 to 50 nm in diameter. Recently, CNOs have gained attention in different fields because of their interesting chemical and physical properties. However, their lack of dispersibility in common solvents due to strong intermolecular interactions limits their applications. Here, we studied the dispersion behavior of CNOs prepared by nanodiamond annealing in 20 solvents of different polarities. Dynamic light scattering and transmission electron microscopy were used to study the dispersion of CNOs in the different solvents. The solvents were classified as “good” or “bad” solvents to determine the Hansen solubility parameters (HSP) of the CNOs using various optimization approaches. The calculated HSPs (δD, δP and δH) were further used to predict the CNO dispersion behavior in other solvents with a very good agreement between expected and observed dispersibilities. Our results will be helpful to estimate the behavior of CNOs in other solvents or their interaction with other materials with known HSPs.