Under solvent saturation, a precipitation of fullgrownsupracrystals on the one hand and the formation of well defined supracrystalline fi lms at the air− liquid interface on the other hand were previously observed for the fi rst time (J. Am. Chem. Soc. 2012 , 134 , 3714− 3719). Here, these two simultaneous growth processes are studied by additional experiments and by Brownian dynamics simulations. The thickness of the supracrystalline films and the concentration of free nanocrystals within the solution are measured as a function of the nanocrystal size. The simulations show that the fi rst process of supracrystal growth is due to a homogeneous nucleation favored by solvent-mediated ligand interactions, while the second one is explained in terms of a diff usion process caused by a decrease in the surface energy when the particles penetrate the air− liquid interface. It is also verifi ed that the presence of thiol molecules at the air− solution interface does not hinder the formation of supracrystalline films.
Source : Simultaneous Interfacial and Precipitated Supracrystals of Au Nanocrystals: Experiments and Simulations. N Goubet, J. Richardi, P.A. Albouy and M. P. Pileni. J.Phys.Chem.B., 2013, 117, 4510!4516 .