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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

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