(139a) Investigation of Ligand Solvation Effects for Alkyl Thiol Stabilized Metal Nanoparticles In CO2 Expanded Liquids Using Small Angle Neutron Scattering

Recent advances in metallic nanoparticle synthesis and processing have opened the door for new opportunities taking advantage of their distinct properties varying from bulk metals. For many of these nanoparticle applications, monodispersity is critical because of their size-dependent functionality. Utilizing CO2 as an anti-solvent for organic solvent dispersed metal nanoparticles, nanoparticles 10nm in diameter or less can be controllably size-fractionated into monodisperse populations. Here, the stabilizing ligands play a major role in the synthesis and application of metallic nanoparticles and allows for dispersion in various solvents. Manipulation of the nanoparticle surface chemistry through synthesis or ligand exchange, affords significant opportunity for solution based ?green? processing and impacts their potential applications; the solvent ? ligand interactions are deterministic of the nanoparticle behavior in solution. We have recently used an interaction energy model to predict the dispersibility of nanoparticles in gas-expanded liquids (GXLs) as a function of the solvent ? ligand interactions; however, questions remain unanswered regarding the stabilizing ligand structure. We have examined the structural properties of alkane thiol stabilizing ligands using Small Angle Neutron Scattering (SANS) as a function of CO2 pressure and thus the nanoparticle dispersibility. SANS was used to determine the local solvation effects of nanoparticles ligands as well as the effective ligand solvation length as a function of the solvent properties.