Nanoparticle Synthesis and Assembly
Nanoparticle synthesis and assembly is the chemistry of making metal and inorganic particles of controlled size and shape in solution and organising them into ordered superstructures.
Definition
Nanoparticle synthesis is the controlled formation of nanometre-scale particles of defined size, shape, and composition, usually in solution; assembly is the organisation of such particles into ordered two- or three-dimensional arrays whose collective behaviour can differ from that of the isolated particles.
Scope
This topic covers the bottom-up, solution-phase preparation of nanoparticles: nucleation and growth in colloidal systems, the role of capping ligands and surfactants in controlling size and shape, reduction and decomposition routes to metal and oxide particles, and the separation of nucleation from growth that yields monodisperse products. It also covers how nanoparticles are directed to assemble — by drying, ligand interactions, or templating — into superlattices and functional films.
Core questions
- How do nucleation and growth control nanoparticle size distribution?
- What role do ligands and surfactants play in shape control?
- How are monodisperse nanoparticles obtained?
- How can nanoparticles be assembled into ordered superstructures?
Key concepts
- Nucleation and growth
- Capping ligands and surfactants
- Monodispersity
- Anisotropic shape control
- Nanoparticle superlattices
- Template-directed assembly
Key theories
- Separation of nucleation and growth
- Monodisperse nanoparticles result when a burst of nucleation is followed by diffusion-limited growth, so all particles grow for the same time; controlling this separation is the basis of colloidal syntheses that yield narrow size distributions.
- Ligand-directed shape control and self-assembly
- Surfactant and capping molecules adsorb selectively on different crystal facets to steer anisotropic growth, and they mediate the interparticle forces that let monodisperse particles self-organise into ordered superlattices on evaporation.
Mechanisms
Reduction or decomposition of a precursor builds up monomer until supersaturation triggers a burst of nuclei; these grow by addition of monomer and by Ostwald ripening, while adsorbed ligands cap surfaces, set the final size, and direct facet-selective growth and subsequent ordered assembly.
Clinical relevance
Controlled nanoparticle synthesis supplies catalysts with tailored facets, plasmonic gold and silver particles for sensing and imaging, magnetic particles for data storage and separations, and the building blocks for metamaterials assembled from ordered nanoparticle arrays.
History
LaMer's mid-twentieth-century model of burst nucleation followed by controlled growth provided the conceptual basis for making monodisperse colloids. Late-twentieth-century advances in coordinating-solvent and surfactant chemistry, summarised by El-Sayed and others, made size and shape routinely controllable, and the resulting uniform particles enabled the study of self-assembled nanoparticle superlattices.
Key figures
- Mostafa El-Sayed
- Victor LaMer
- Geoffrey Ozin
Related topics
Seminal works
- elsayed2005
- ozin2009
Frequently asked questions
- Why is separating nucleation from growth important for uniform nanoparticles?
- If new particles keep nucleating while others grow, the final population spans a wide range of ages and therefore sizes. Concentrating nucleation into a brief burst, after which only growth occurs, ensures all particles grow for nearly the same time and end up nearly the same size.
- What holds a nanoparticle superlattice together?
- Ordered nanoparticle arrays are held together largely by interactions between the organic ligands coating the particles, together with van der Waals attraction between the inorganic cores. These soft, tunable forces let monodisperse particles pack into crystalline superlattices much as atoms pack into a crystal.