Interparticle\nLigand Exchange Kinetics Revealed by\nTime-Resolved SANS

Interparticle\nligand exchange can occur during the formation\nof\nnanoparticle superlattices (NPSLs), affecting the symmetry of the\nNPSLs. Here, we report time-resolved small-angle neutron scattering\n(TR-SANS) measurements of the interparticle exchange kinetics of thiolate\nligands among gold nanoparticles (AuNPs) at different temperatures.\nTo track the ligand exchange among AuNPs, two groups of AuNPs were\nfunctionalized with hydrogenated and deuterated dodecanethiol, respectively,\nand then mixed in a solvent mixture of toluene and deuterated toluene\nfor shell contrast. The interparticle ligand exchange barely occurred\nat 25 °C even after 40 h, but 11%, 34%, and 74% occurred at 50,\n60, and 70 °C, respectively. At 80 °C, the exchange saturated\nafter 20 h. The exchange process follows first-order kinetics, and\nits activation energy is estimated to be 29.1 kcal/mol, supporting\nthat ligand desorption is a rate-determining step. These findings\ncan be used as valuable reference data, aiding in the design and understanding\nof NPSLs.