Homogeneous and Disordered Assembly of Densely Packed Nanocrystals

A homogeneous and disordered assembly of densely packed nanocrystals is generated without the assistance of organic molecules, from an aqueous solution at room temperature. The densely packed nanocrystals of tin dioxide (SnO2) and titanium dioxide (TiO2), 2-3 nm in size, form glassy macroscopic transparent objects of 2-10 mm. The monodisperse nanocrystals, which have a surface hydrated layer and are synthesized in aqueous solution, are densely packed in an homogeneous and disordered assembly through the evaporation of water as the dispersion medium. The formation of transparent bulk objects on the macroscopic scale originates from the homogeneous and disordered nature of the densely packed nanocrystals. The resultant homogeneous architectures are distinguishable from the typical inhomogeneous and disordered aggregates of nanoparticles observed after evaporation of the dispersion medium. Among superstructures based on nanocrystals, such as superlattices and mesocrystals, the resultant homogeneous and disordered assembly can be regarded as a new class of solid-state material.