Self-assembled 3D free-standing superlattices of gold nanoparticles driven by interfacial instability of emulsion droplets

Three-dimensional (3D) superlattice materials self-assembled from functional inorganic nanoparticles (NPs) have attracted extensive attention due to the unique properties of the building blocks and additional intriguing collective properties derived from the interaction between adjacent NPs. However, the spontaneous assembly of inorganic NPs into 3D free-standing plasmonic superlattices still remains an enormous challenge. Herein, we report a facile and universal strategy to assemble gold nanoparticles (AuNPs) tethered with polystyrene (PS) and poly(2-vinylpyridine) (P2VP) homopolymers into 3D free-standing sheet-like superlattices by systematically tuning the oil/water interfacial tension and the interfacial instability of emulsion droplets. The prepared sheet-like superlattices are multilayer and the AuNP building blocks stack as tetrahedra, in which each AuNP building block is partially sitting on the three other nearby nanoparticles. Moreover, the interparticle distance between adjacent NPs can be effectively regulated by varying the molecular weight of the tethered PS ligands on the surface of AuNPs. This template-free approach provides a novel and effective route to manipulate nanoparticles into free-standing ordered 3D superlattices with a wide range of potential applications.