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