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Observations of nanoparticle superlattice formation over minutes during colloidal nanoparticle synthesis elude description by conventional understanding of self-assembly, which theorizes superlattices require extended formation times to allow for diffusively driven annealing of packing defects. It remains unclear how nanoparticle position annealing occurs on such short time scales despite the rapid superlattice growth kinetics. Here we utilize liquid phase transmission electron microscopy to directly image the self-assembly of platinum nanoparticles into close packed supraparticles over tens of seconds during nanoparticle synthesis. Electron-beam induced reduction of an aqueous platinum precursor formed monodisperse 2–3 nm platinum nanoparticles that simultaneously self-assembled over tens of seconds into 3D supraparticles, some of which showed crystalline ordered domains. Experimentally varying the interparticle interactions ( e.g. , electrostatic, steric interactions) by changing precursor chemistry revealed that supraparticle formation was driven by weak attractive van der Waals forces balanced by short ranged repulsive steric interactions. Growth kinetic measurements and an interparticle interaction model demonstrated that nanoparticle surface diffusion rates on the supraparticles were orders of magnitude faster than nanoparticle attachment, enabling nanoparticles to find high coordination binding sites unimpeded by incoming particles. These results reconcile rapid self-assembly of supraparticles with the conventional self-assembly paradigm in which nanocrystal position annealing by surface diffusion occurs on a significantly shorter time scale than nanocrystal attachment.
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Molecular Additives as Competitive Binding Agents to Control Supramolecular-Driven Nanoparticle Assembly
Colloidal nanoparticle assembly methods can produce intricate superlattice structures and often use knowledge of atomic crystallization behaviors to guide their design. While this analogy has enabled multiple routes to programming colloidal crystallization thermodynamics, fewer tools or strategies exist to manipulate nanoparticle superlattice growth kinetics in a controlled manner. Here we investigate how small molecule additives can be used to modulate the thermodynamics and kinetics of supramolecular-chemistry-driven nanoparticle assembly. Specifically, we introduce monovalent binding agents into the superlattice growth solution that compete with the multivalent interparticle bonding interactions driving particle assembly, thereby altering interparticle bond strength by reducing the number of bridging complexes formed between particles. In this manner, the assemblies can be steered to avoid kinetic traps and crystallize into faceted single crystals under isothermal conditions, alleviating the need for precise thermal control that has conventionally been required to produce large, faceted crystals in prior assembly methods.
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- Award ID(s):
- 2304909
- PAR ID:
- 10626859
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- ACS Nanoscience Au
- Volume:
- 4
- Issue:
- 6
- ISSN:
- 2694-2496
- Page Range / eLocation ID:
- 374 to 380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acsnanoscienceau.4c00062
