Interparticle Ligand Exchange Kinetics Revealed by Time-Resolved SANS

Interparticle ligand exchange can occur during the formation of nanoparticle superlattices (NPSLs), affecting the symmetry of the NPSLs. Here, we report time-resolved small-angle neutron scattering (TR-SANS) measurements of the interparticle exchange kinetics of thiolate ligands among gold nanoparticles (AuNPs) at different temperatures. To track the ligand exchange among AuNPs, two groups of AuNPs were functionalized with hydrogenated and deuterated dodecanethiol, respectively, and then mixed in a solvent mixture of toluene and deuterated toluene for shell contrast. The interparticle ligand exchange barely occurred at 25 °C even after 40 h, but 11%, 34%, and 74% occurred at 50, 60, and 70 °C, respectively. At 80 °C, the exchange saturated after 20 h. The exchange process follows first-order kinetics, and its activation energy is estimated to be 29.1 kcal/mol, supporting that ligand desorption is a rate-determining step. These findings can be used as valuable reference data, aiding in the design and understanding of NPSLs.