Nanoparticle Clusters with Lennard-Jones Geometries

Abstract

Noble gas and metal atoms form minimum-energy clusters. Here, we present analogous agglomerates of gold nanoparticles formed in oil-in-water emulsions. We exclude interfacial templating and nucleation-and-growth as formation mechanisms of these supraparticles. Similar to atomic clusters, the supraparticles form when a mobile precursor state can reconfigure until the nanoparticles' interactions with each other and with the liquid-liquid interface are maximized. This formation mechanism is in striking contrast to that previously reported for microparticle clusters.

Colloidal matter: Packing, geometry, and entropy

“…The Lennard-Jones 6-12 and related potentials are reasonable approximations for certain nanoparticles (76) but are poor models for colloids, which have much shorter-range attractions. Moreover, entropy must play a role in structuring colloids, even when the potential is attractive.…”

Structure diagram of binary Lennard-Jones clusters

“…It is known that the structure of minimal energy clusters depends sensitively on the form of the interaction potential 14,15 . As colloidal agglomeration experiments have been shown to produce minimal energy Lennard-Jones cluster structures 12 we conclude that the interactions between the nanoparticles in this type of experiment can be modeled by effective LennardJones interactions and that the interactions are strong in comparison to the thermal energy, such that the ground state is formed at room temperature.…”

“…With this we determine the structural behavior that is to be expected for mixtures of spheres with dissimilar attractions in e.g. confined agglomeration experiments with ligand coated bimetallic nanoparticles where the composition in an individual emulsion droplet is fixed 12 . In figures 2, 3 and 4 we present diagrams of several measures that characterize the structure of the clusters for two different material dissimilarities.…”

Pressure-controlled formation of crystalline, Janus, and core–shell supraparticles

“…Mixtures of particles have not yet been assembled inside emulsions, although uniform nanoparticle dispersions confined to the dispersed phase of an emulsion form welldefined clusters known as supraparticles. 4,7,8 Similar structures have been created by drying droplets on superamphiphobic surfaces. 8 In this contribution, we study the structure of binary supraparticles that form inside emulsions.…”

“…[1][2][3] Binary mixtures of uniform particles thus arrange at liquid-air interfaces, 1 liquid-liquid interfaces, 3 and inside droplets. 4 Self-assembly can be explained by a combination of entropic space-filling arguments and minimization of the interparticle potentials, with relative contributions that depend on the particle core, ligand shell, solvent, and process parameters. The large parameter space leads to a remarkable structural diversity of the superstructures.…”