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.

The distribution of narrowly dispersed gold nanoparticles in hexane-in-water emulsions was studied for different surfactants. Good surfactants such as SDS and Triton X-100 block the oil-water interfaces and confine particles in the droplet. Other surfactants (Tween 85 and Span 20) form synergistic mixtures with the nanoparticles at the interfaces that lower the surface tension more than any component. Supraparticles with fully defined particle distribution form in the droplets only for surfactants that block the interface. Other surfactants promote the formation of fcc agglomerates. Nanoparticles in emulsions behave markedly different from microparticles-their structure formation is governed by free energy minimization, while microparticles are dominated by kinetics.

International audienceInsulated molecular wires formed from organic molecules may have promising applications in organic and flexible electronic devices. Here, the authors provide compelling evidence of the formation of insulated molecular wires by sheathing conducting regioregular poly(3-butylthiophene-2,5-diyl) (P3BT) fibrils with insulating nanotubes from 3,5-bis-(5-hexylcarbamoylpentyloxy)-benzoic acid decyl ester molecules through a nucleation and growth process. For dilute systems, conducting atomic force microscopy together with force-distance curves and current-voltage spectroscopy are concomitantly performed to sense current from the topmost surface to the core of the composite fibrils at controlled tip indentation depths. Results show that current is sensed only when the core of the nanocomposite fibrils is reached which indicates the presence of an insulating layer around the semiconducting P3BT fibrils. The existence of this molecular nanocomposite is further supported by neutron scattering experiments carried out on more concentrated systems at different temperatures

The ageing of spherical gold nanoparticles having 6‐nm‐diameter cores and a ligand shell of dodecanethiol is investigated under different storage conditions. Losses caused by agglomeration and changes in optical particle properties are quantified. Changes in colloidal stability are probed by analytical centrifugation in a polar solvent mixture. Chemical changes are detected by elementary analysis of particles and solvent. Fractionation occurs under all storage conditions. Ageing is not uniform but broadens the property distributions of the particles. Small‐number statistics in the ligand shell density and the morphological heterogeneity of particles are possible explanations. Washing steps exacerbate ageing, a process that could not be fully reversed by excess ligands. Dry storage is not preferable to storage in solvent. Storage under inert argon atmosphere reduces losses more than all other conditions but could not prevent it entirely.