(42f) Oriented Attachment of Ag Nanoplates: A Molecular Dynamics Study

The oriented attachment mechanism, in which solution-phase nanocrystals associate along preferred crystallographic directions to form a single-crystal aggregate, has enabled the synthesis of asymmetric nanostructures, such as nanoplates and nanorods. Although there have been numerous observations of oriented attachment, its mechanistic origins remain elusive. We investigate the role of polyvinylpyrrolidone (PVP) in the oriented attachment of Ag nanoplates using molecular dynamics (MD) simulations and potential-of-mean-force calculations based on a many-body force field for organic-metal interactions. In the analogous experimental system, triangular Ag nanoplates tend to laterally attach to each other at the edges, forming large planar nanostructures. Our MD simulations of PVP-covered triangular Ag nanoplates show that the PVP density is greater on the large, flat faces compared to the edges. The difference in PVP density between the flat faces and edges increases with PVP's chain length, which suggests that configurational entropy causes PVP molecules to prefer the flat faces. From our potential-of-mean-force calculations, the free-energy barrier for Ag nanoplates to laterally attach at the edges is smaller in both height and width, compared to attachment between the flat faces. We also observe a local minimum before the energy barrier where the PVP molecules from each plate associate and form bridges between the plates, for both lateral and vertical attachment. Our results suggest that oriented attachment between Ag nanoplates is driven by kinetics, in which the preference for lateral attachment is a consequence of the denser PVP layer on the flat faces.