Coalescence of Au Nanoparticles without Ligand Detachment.

Repulsion of ligands is known as the key factor for hindering nanoparticle (NP) coalescence. Thus, during the past decade, it has generally accepted that the full removal of capping ligands of the contact surface is the first step for NP coalescence. Herein, using molecular dynamics simulations, we have identified a new mechanism for the coalescence of S(CH_{2})_{n}COOH-coated Au NPs in water without ligand detachment. In contrast to the traditional mechanism, the aggregation of the NPs is induced by the twined hydrophobic chains of the ligands rather than the hydrophilic carboxyl tails as believed previously. Next, the exposed surface atoms attach to form the neck, and extend with the atomic rearrangement of the contact interface to merge the NPs, which do not need the removal of ligands as expected from traditional supposition. This finding refreshes the understanding of the atomic mechanism of the coalescence of NPs, which paves the way for the rational design and synthesis of NPs.