The Nanocube Assemblies at Liquid-Liquid Interfaces

We investigated the assembly dynamics of carboxy-functionalized Fe3O4 nanocubes (NCs) at oil-water interface, where the hydrophilic nanocubes interact with an oil-soluble cationic surfactant, amine-modified polystyrene (PS-NH2), to form the nanocube surfactants, NCSs. We generated densely packed monolayers of Fe3O4 nanocube surfactants, exploring the impact of key parameters, such as the type of surfactant types, pH, ionic strength of the aqueous phase, the size of the nanocube, and concentrations of the nanocubes and ligands. It was found that the attachment of ligands to the NCs will invariably slow the rotational dynamics of nanocube surfactants that also impacts the interactions between nanocube surfactants anchored to the interface. Not only does the adsorption of the individual nanocubes impacts the order of the assembly, but also the ultimate packing density of the assemblies. This provides an opportunity to control the packing of nanocube surfactant assembly, by manipulating the spatial constraints imposed by the anisotropic shape of the nanocubes and their collective behavior in the assemblies.