Formation of Superlattices of Gold Nanoparticles Using Ostwald Ripening in Emulsions: Transition from fcc to bcc Structure

Abstract

An efficient method to form 3D superlattices of gold nanoparticles inside oil emulsion droplets is presented. We demonstrate that this method relies on Ostwald ripening, a well-known phenomenon occurring during the aging of emulsions. The key point is that the nanoparticle concentration inside the smaller droplets is increasing very slowly with time, thus inducing the crystallization of the nanoparticles into superlattices. Using oil-in-water emulsions doped with hydrophobic gold nanoparticles, we demonstrate that this method is efficient for different types of oils (toluene, cyclohexane, dodecane, and hexadecane). 3D superlattices of the nanoparticles are obtained, with dimensions reaching a hundred nanometers. The kinetics of the crystallization depends on the solubility of the oil in water but also on the initial concentration of the gold nanoparticles in oil. This method also provides an innovative way to obtain the complete phase diagram of nanoparticle suspensions with concentration. Indeed, during this slow crystallization process, a transition from a disordered suspension to a fcc structure is observed, followed by a transition toward a bcc structure. This evolution with time provides key results to understand the role played by the ligands located at the surface of the nanoparticles in order to control the type of superlattices which are formed.

Controlling the symmetry of supercrystals formed by plasmonic core–shell nanorods with tunable cross-section

“…[3][4][5] For instance, a transition from an FCC to a BCC phase and even complex Frank-Kasper phases were observed in crystals of small hydrophobic gold nanoparticles. [6][7] Another group achieved continuous symmetry variation from simple cubic to rhombohedral phases by changing the ligand excess in the solution. 8 While the "soft shell" strategy is successful for small and isotropic nanoparticles, only little success has yet been obtained with large and/or anisotropic building blocks.…”

Isotropic Huygens dipoles and multipoles with colloidal particles

“…Several recent examples show that it is possible to selfassemble plasmonic nanoparticles in clusters of submicrometric sizes [29][30][31] . The cluster system is rich as it is scalable and its optical properties can be tuned by varying the nature, amount, size and volume fraction of inclusions.…”

Enhancement on the Surface Hydrophobicity and Oleophobicity of an Organosilicon Film by Conformity Deposition and Surface Fluorination Etching

“…The particles distributed over the surface of the as-deposited Ag seed layer ( Figure 2 a) are densely and tightly packed, whereas round and separated nanoparticles were observed from the surface of the annealed samples. As quoted from the reports, the formation of these isolated Ag nanoparticles was ascribed to the compressive stress induced by the annealing treatment and the Ostwald ripening mechanism [ 28 , 29 ]. It was also evident that the size of these nanoparticles was increased with the deposition time of the Ag seed layer increasing.…”