%0 Online Multimedia %A Yang, Chih-Wen %A Chiu, Chun-Ya %A Huang, Michael H. %D 2014 %T Formation of Free-Standing Supercrystals from the Assembly of Polyhedral Gold Nanocrystals by Surfactant Diffusion in the Solution %U https://acs.figshare.com/articles/media/Formation_of_Free_Standing_Supercrystals_from_the_Assembly_of_Polyhedral_Gold_Nanocrystals_by_Surfactant_Diffusion_in_the_Solution/2261149 %R 10.1021/cm502451u.s004 %2 https://ndownloader.figshare.com/files/3897145 %K SolutionGold supercrystals %K Gradual diffusion %K Supercrystal growth %K polyhedral supercrystals %K polyhedral morphologies %K CTAC concentration %K nanocrystal droplet %K particle aggregation %K supercrystal formation process %K rhombic dodecahedral nanocrystals %K gold octahedra %K CTAC solution %K particle solution %K Eppendorf tube %K nanocrystal solution %K Surfactant Diffusion %K water droplet evaporation %K diffusional surfactant transport approach %K surfactant concentration %K Polyhedral Gold Nanocrystals %K nanocrystal systems %K supercrystal formation %K cetyltrimethylammonium chloride %K transmission electron microscopy examination %K face contact %X Gold supercrystals with polyhedral morphologies can be prepared from the ordered packing of octahedral and rhombic dodecahedral nanocrystals in the presence of a sufficient amount of surfactant by slow water droplet evaporation. The whole supercrystal formation process has been video-recorded using a specially designed chamber to enclose a substrate containing the nanocrystal droplet in a moist environment. Supercrystal growth from the assembly of octahedra is completed within a shorter time. The presence of cetyltrimethylammonium chloride (CTAC) within the supercrystals has been confirmed by small-angle X-ray diffraction analysis. Transmission electron microscopy examination reveals the tendency of two gold octahedra with face contact to fuse, a process frequently observed in the formation of octahedron-assembled supercrystals. Remarkably, we have developed a diffusional surfactant transport approach to make free-standing supercrystals in bulk aqueous solution by adding a concentrated CTAC solution to a concentrated particle solution with a lower CTAC concentration in an Eppendorf tube. Gradual diffusion of CTAC to the lower nanocrystal solution promotes the growth of polyhedral supercrystals. A solution with a sufficiently high surfactant concentration has been shown to be necessary for particle aggregation and supercrystal formation. This method allows the deposition of dense but evenly distributed supercrystals on a substrate. Supercrystals were also used to make a modified electrode for electro-oxidation of glucose. This simple and organic solvent-free approach to making a large quantity of supercrystals allows an ample supply of supercrystals for studies of densely assembled nanocrystal systems and for biomedical applications. %I ACS Publications