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Reversible Kirkwood–Alder Transition Observed in Pt3Cu2 Nanoctahedron Assemblies under Controlled Solvent Annealing/Drying Conditions

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journal contribution
posted on 2012-08-29, 00:00 authored by Jun Zhang, Zhiping Luo, Benjamin Martens, Zewei Quan, Amar Kumbhar, Nathan Porter, Yuxuan Wang, Detlef-M. Smilgies, Jiye Fang
We report a Kirkwood–Alder transition in a system of nonspherical Pt3Cu2 nanoctahedra coated with oleic acid and oleylamine ligands. Using both transmission electron microscopy tomography with 3D reconstruction analysis and synchrotron-based in-situ grazing-incidence small-angle X-ray scattering (GISAXS) techniques, we specifically determined that these nanoctahedra can assemble into an open structure in which the nanoctahedra are arranged tip-to-tip to form a bcc superlattice with a low packing efficiency. Using in-situ and real-time GISAXS, we further observed a “nanoctahedron crystallization” as a soft Kirkwood–Alder transition, that is, the soft nanoactahedra crystallize at a critical concentration and possess continuous crystalline states during a period of solvent evaporation. Finally, we found a reversible change of the superlattice constant during the solvent annealing and evaporation/drying processes.