Evolution of the Ligand Shell Morphology during Ligand Exchange Reactions on Gold Nanoparticles.

Ligand exchange reactions are used to achieve nanoparticles coated with a mixture of ligand molecules. Currently, nothing is known on the evolution of the morphology of the ligand shell during the reaction. Here, we use a recently developed method (based on MALDI-TOF) to follow the evolution of the ligand shell composition and morphology during the reaction. We observe the expected evolution in composition and we find that the ligand shell starts as a random mixture and gradually evolves towards a patchy morphology. When the composition has reached a plateau (i.e. when the reaction is generally assumed to be finished), the ligand shell morphology keeps evolving for days, slowly approaching its equilibrium configuration.