Interparticle Ligand Exchange Kinetics Revealed by Time-Resolved SANS.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Nanoparticle superlattices (NPSLs) are ordered assemblies with properties dependent on interparticle interactions.
• Interparticle ligand exchange can influence NPSL symmetry and overall structure.
• Understanding ligand exchange kinetics is crucial for controlling NPSL formation and properties.

Purpose of the Study:

• To quantify the kinetics of interparticle thiolate ligand exchange among gold nanoparticles (AuNPs).
• To investigate the effect of temperature on ligand exchange rates.
• To determine the activation energy of the ligand exchange process.

Main Methods:

• Time-resolved small-angle neutron scattering (TR-SANS) was employed to monitor ligand exchange.
• Gold nanoparticles (AuNPs) were functionalized with hydrogenated and deuterated dodecanethiol for contrast.
• Experiments were conducted in a toluene/deuterated toluene solvent mixture at various temperatures (25-80 °C).

Main Results:

• Ligand exchange was minimal at 25 °C but increased significantly with temperature (11% at 50 °C, 34% at 60 °C, 74% at 70 °C).
• Exchange reached saturation at 80 °C within 20 hours.
• The exchange process followed first-order kinetics with an activation energy of 29.1 kcal/mol.

Conclusions:

• Ligand desorption is the rate-determining step in the interparticle ligand exchange process.
• Temperature is a critical factor controlling ligand exchange kinetics in AuNP systems.
• These findings provide valuable data for designing and understanding nanoparticle superlattices.