PNNL

Abstract

In this work, we explore the dispersibility of octanethiol-stabilized gold nanocrystals of different core sizes in compressed ethane and propane over a wide range of fluid conditions. The dispersibility of the nanocrystals was obtained through the Surface Plasmon Resonance (SPR) absorption spectra of solutions. Three models, the total interaction theory, the sedimentation coefficient equation, and the Chrastil method, are briefly discussed as tools to interpret the experimental results. Nanoparticle dispersibility-versus-density plots are strongly dependent on nanoparticle size and solvent conditions, with the dispersion of larger nanocrystals more dependant on changes of pressure or density at a given temperature. These results showed a notable correlation with the calculated sedimentation coefficients of the nanocrystals in both solvents. The Chrastil equation was successfully applied to predict and describe the dispersibility of the gold nanocrystals as a function of density, showing that the high stabilities of the nanocrystals dispersions are a result of the very strong solvent-nanocrystal interactions. For the range of nanoparticle sizes studied, compressed ethane at 25 ºC led to a greater tunability of nanoparticle dispersion when compared with compressed propane at 65 ºC. On the other hand, for equivalent pressures compressed propane was found to provide better solubility than ethane due to its higher density. The results of this study quantitatively demonstrate that compressed fluids can offer pressure tunable, size selective control of nanoparticle solvation and transport. This ability has clear advantages over conventional solvents and direct application to various nanomaterials processes, such as separation, transport and purification of nanocrystals.