Small-Angle Neutron Scattering of Silver Nanoparticles in Gas-Expanded Hexane

Stabilizing ligands play a major role in the synthesis and stabilization of metallic nanoparticles, allowing dispersibility in various solvents including gas-expanded liquids (GXLs). Interaction energy modeling has been used to predict the dispersibility of hydrophobically stabilized metal nanoparticles in GXLs but often overpredicts the mean particle size dispersed at a given solvent composition. More accurate and robust interaction energy models can be developed if the changes to both the ligand length and ligand solvation as a response to the composition of GXLs are better understood. Small-angle neutron scattering (SANS) is a unique technique for nanoparticle characterization where in-situ ligand solvation measurements can be obtained by contrasting hydrogenated nanoparticle ligands with deuterated solvent. This study presents the first in-depth SANS measurements of ligand length and ligand solvation variation during nanoparticle antisolvent precipitation. The focus of this investigation is dodecanethiol-stabilized silver nanoparticles in carbon dioxide (CO2)-expanded hexane. Upon pressurization with CO2 antisolvent, the ligand length and ligand solvation for dodecanethiol-capped silver nanoparticles decrease as a function CO2 composition in the GXL prior to nanoparticle precipitation. This work discusses the dependence of nanoparticle dispersibility as a function of CO2 composition in n-hexane-d(14) GXL and the competing roles of ligand surface coverage, ligand length, and ligand solvation for nanoparticles with varying surface curvature.