Dimensionality-controlled self-assembly of CdSe nanorods into discrete suprastructures within emulsion droplets

Self-assembly of inorganic nanocrystals into ordered superlattices is of particular importance for their application in biomedicine and solid-state optoelectronic devices. However, dimensionality-controlled self-assembly of nanocrystals is still in its infancy. Emulsion-droplet confined self-assembly could offer a solution considering that the liquid/liquid interface and inner compartments can be respectively used as 2D and 3D templates for the assembly of nanocrystals, producing assemblies with a controlled dimensionality. CdSe nanorods with different aspect ratios were synthesized, and were applied as building blocks to uncover their assembly modes within the o/w emulsion droplets. The results reveal that by using both hydrophilic and lipophilic surfactants, hydrophobic CdSe nanorods can be locked at the liquid/liquid interface to produce a 2D supracrystalline sheet. In contrast, hydrophilic surfactants alone can result in the formation of 3D supracrystalline spherical colloids in similar conditions. Lipophilic surfactants, such as octylamine, can interact with the alkyl chains coated on the CdSe nanorods strongly, which consequently modulates the assembly mode of nanorods within the emulsion droplets. By considering the soft coatings of these supracrystalline structures with two different dimensionalities, these materials could be ideal candidates for the study of their interactions with biological soft matter.