Tuning of mechanical properties of Au supracrystal

Forces
Tuning of mechanical properties of
Au supracrystal using coating ligand
interaction.
M. Gauvin, Y. Wan, I. Arfaoui, M. P. Pileni*
Laboratoire des Matériaux Mésoscopiques et Nanométriques
(LM2N), UMR CNRS 7070, Université Pierre et Marie Curie, bât F, BP
52, 4 place Jussieu, 75252 Paris Cedex 05, France
Here, we investigate mechanical properties of fcc colloidal crystals of Au
nanocrystals, called supracrystals, differing by their nanocrystal size (d),
coating chain length (n) and interparticle distance (δpp), using
nanoindentation measurements performed with an Atomic Force
Microscope. A continuous mechanical model is used to calculate Young’s
modulus and hardness values of Au supracrystals deposited on silicon
substrate and the influence of the substrate on nanoindentation
measurements is taken into account. Their Young’s modulus (E) and
hardness (H) are in the range of few tenth of MPa to a few GPa
corresponding to polymer-like mechanical properties. E and H values
decrease as d increases from 5nm to 7nm. Mechanical properties
markedly increase on increasing the coating agent chain length n from
12 to 14. A scaling theoretical model that describes the conformation of
coating chains in solution is used to qualitatively explain this trend.
Under different experimental conditions used to produce supracrystals,
this trend disappears in swollen supracrystals characterized by a ~ 50%
increase of their δpp. These results show that mechanical properties of
supracrystals deviate from classical nano-composite material and
emphasize the important role of cohesive interactions between
nanocrystals mediated by flexible coating ligand.
September 9, 2013
Salle des Conseils (23rd floor)
Zamanski Tower,
Place Jussieu,
75005 Paris
www.supranano.fr