Compression stiffness of porous nanostructures from self-assembly of branched nanocrystals.

The novelty and potential of self-assembled superstructures reside not only in the more commonly investigated optical, magnetic and charge transport properties, but also in their mechanical behaviour, which is strictly dependent on their structural morphology. We report here nanocompression tests on highly porous, geometrically interlocked superstructures fabricated by self-assembly of colloidal CdSe/CdS octapod shaped nanocrystals. We show that, despite being formed via weak van der Waals forces, these superstructures present an elastic response similar to that of porous materials and indeed were found to be modelled fittingly by classical open-cell models. The simple model based on the relative density of the superstructures holds also when the chemical composition of the superstructures is modified by processes such as cation exchange of Cd(2+) with Cu(+) and oxygen plasma treatment.