Ligand-Dependent Coalescence Behaviors of Gold Nanoparticles Studied by Multichamber Graphene Liquid Cell Transmission Electron Microscopy

The
formation mechanism of colloidal nanoparticles is complex because
significant nonclassical pathways coexist with the conventional nucleation
and growth processes. Particularly, the coalescence of the growing
clusters determines the final morphology and crystallinity of the
synthesized nanoparticles. However, the experimental investigation
of the coalescence mechanism is a challenge because the process is
highly kinetic and correlates with surface ligands that dynamically
modify the surface energy and the interparticle interactions of nanoparticles.
Here, we employ quantitative in situ TEM with multichamber
graphene liquid cell to observe the coalescence processes occurring
in the synthesis of gold nanoparticles in different ligand systems,
thus affording us an insight into their ligand-dependent coalescence
kinetics. The analyses of numerous liquid-phase TEM trajectories of
the coalescence and MD simulations of the ligand shells demonstrate
that enhanced ligand mobility, employing a heterogeneous ligand mixture,
results in the rapid nanoparticle pairing approach and a fast post-merging
structural relaxation.