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Séminaire de Mélanie Gauvin

Tuning mechanical properties of colloidal crystals of Au nanocrystals using coating ligand interactions


Tuning mechanical properties of colloidal crystals of Au nanocrystals using coating ligand interactions

M.Gauvin (a,b), Y.Wana, I.Arfaoui (a) and M-P. Pileni * (a)

a) Laboratoire des Matériaux Mésoscopiques et Nanométriques, UMR CNRS 7070, UPMC
b) Laboratoire de Physique et Chimie des Nano-Objets, UMR CNRS 5215, INSA Toulouse
*marie-paule.pileni@upmc.fr

Colloidal crystals fabricated with nanocrystals as building blocks, called supracrystals or supercrystals, show optical, magnetic and electronic properties that benefit from a combination of individual and collective properties of nanocrystals in their assemblies. Controlling the structure and multi-scale interactions in supracrystals is an exciting route to achieve new materials with tunable physical properties.
Here, we investigate mechanical properties of face centered cubic colloidal crystals of Au nanocrystals differing by their nanocrystal size, coating chain length and edge-to-edge interparticle distance, using nanoindentation measurements performed with an Atomic Force Microscope. Their Young’s modulus (E) and hardness (H) are in the range of few tenths of a MPa to a few GPa corresponding to polymer-like mechanical properties. E and H values decrease as nanocrystal size increases from 5nm to 7nm. Mechanical properties markedly increase on increasing the coating chain length. A scaling theoretical model that describes the conformation of coating chains in solution is used to qualitatively explain this trend. These results show that mechanical properties of colloidal crystals of Au nanocrystals deviate from classical nano-composite materials and emphasize the important role of cohesive interactions between nanocrystals mediated by flexible coating ligands.