Introducing Normalized Centrifugation for a More Accurate Thermodynamic Analysis of Molybdenum Disulfide Dispersions: A Study on Mixed Solvents of Alcohols and Amines with Water.

A more accurate solution thermodynamic analysis of colloidal molybdenum disulfide (MoS2) nanosheets dispersed in 91 combinations of organic solvent (alcohols and amines)/water mixtures is made possible by the application of a viscosity- and density-normalized centrifugation method to the post-sonication stock solution. This centrifugation method accounts the solvent mixture's density and viscosity in order to apply different centrifugation times based on Stoke's law and in effect eliminates the kinetic interferences arising from different densities and viscosities of the solvent mixtures used as the dispersing media. This allows us to reveal that the solvent's molecular size and hydrogen-bonding strength are additional important factors that determine the Gibbs free energy of mixing, other than the matching of the Hansen solubility parameters between the dispersed nanosheet and the dispersing medium. In addition, ζ potential turns out to be a negligible factor for the nanosheet dispersibility since surface charges are mainly localized on the edge sites. This is because restacking mainly occurs via the basal planes, which are virtually chargeless. This study further extends our understanding of the dispersibility mechanism of 2D nanosheets in various solvent/water mixtures.