peer journals

Mechanical properties of Au supracrystals tuned by flexible ligand interaction. 

Here mechanical properties of face cubic centered colloidal crystals obtained out of equilibrium by solvent evaporation of coated Au nanocrystals suspension, called supracrystals, are reported as a function ligand chain length (n ) and interparticle edge-to-edge distance within the supracrystals (δpp ) for two nanocrystal sizes (d ). Young’ s modulus (E* ) and hardness (H ) are independent of δpp  and of the supracrystal morphology. Both E*  and H  are in the range of few tenths of a MPa to a few GPa. Tuning of δpp  by 50% is achieved by controlling the solvent vapor pressure (Pt ) during the evaporation process. For any nanocrystal size, at Pt  = 0, E*and H  values markedly increase with increasing n  from 12 to14. At Pt = 39% and 75%, such dependency disappears. This trend diff ers from classical nanocomposite materials and is attributed to a change in the conformation of fl exible ligands with n  and to free thiol-containing molecules trapped in the supracrystallattices.

Source : Mechanical properties of Au supracrystals tuned by flexible ligand interaction.  M.Gauvin, Y. Wan, I. Arfaoui and M.P. Pileni J.Phys.Chem.C.,2014, 118, 5005−5012

peer journals

Hierarchy in Au Nanocrystal Ordering in Supracrystal: III. Competition between Van der Waals and Dynamic Processes.

Au nanocrystals coated with thiol derivatives of varying chain sizes ranging from C12  to C16  were produced; two different size nanocrystals have been synthesized (5 and 7 nm in diameter) for each coating agent. All of those specimensare characterized by a low size distribution (below 7%). ThoseAu nanocrystals were used as building blocks to grow larger self-assembled crystalline structures or supracrystals. Thesecrystalline growths were carried out by slow and controlledsolvent evaporation at different temperatures and under nonnull partial solvent vapor pressure (Pt). We show that theorder within the supracrystals is temperature-dependent whenthey are made of hexadecanethiol-coated gold nanocrystals, regardless of the size of the nanocrystals. The interparticle distances within the various supracrystals that were produced were determined by small-angle X-ray diff raction (SAXRD). We demonstrate that the interparticle distance is controlled not only by the presence of physisorbed thiol residues, as previously reported, but also, at higher temperatures, by the dynamics of the organic chains and the van der Waals forces involved between the metallic cores of the nanocrystals forming the structure.

Source : Hierarchy in Au Nanocrystal Ordering in Supracrystal: III. Competition between Van der Waals and Dynamic Processes. N. Schaeffer, Y.Wan, M.P. Pileni. Langmuir ,2014, 30, 7177 (2014).

peer journals

Water-Dispersed Hydrophobic Au Nanocrystal Assemblies with a Plasmon Fingerprint

Hydrophobic Au nanocrystal assemblies (both ordered and amorphous) were dispersed in aqueous solution via the assistance of lipid vesicles. The intertwine between vesicles and Au assemblies was made possible through a careful selection of the length of alkyl chains on Au nanocrystals. Extinction spectra of Au assemblies showed two peaks that were assigned to a scattering mode that red-shifted with increasing the assembly size and an absorption mode associated with localized surface plasmon, that was independent of their size. This plasmon fingerprint could be used as a probe for investigating the optical properties of such assemblies. Our water-soluble assemblies enable exploring a variety of potential applications including solar energy and biomedicine.

Source : Water-Dispersed Hydrophobic Au Nanocrystal Assemblies with a Plasmon Fingerprint. Yang, C.Deeb, J.L Pelouard, N. Felidj and M.P. Pileni ACS Nano, 2017,11, 7797−7806.