Electrostatic Self-Assembly of Nanoparticles into Static and Out-of-Equilibrium Materials

Self-assembly of inorganic nanoparticles into ordered structures (superlattices) has led to a wide range of nanomaterials with unique optical, magnetic, electronic, and catalytic properties. Various interactions have been employed to direct the crystallization of NPs, including van der Waals forces, hydrogen bonding, as well as electric and magnetic dipolar interactions. Among them, Coulombic interactions have remained largely underexplored, owing to the rapid charge exchange between nanoparticles bearing high densities of opposite charges (superionic nanoparticles). In this talk, I will describe a new method to assemble superionic nanoparticles under conditions (room temperature, concentrated salt solutions) that preserves their native surface charge density. Under these conditions, the Coulombic interactions between superionic nanoparticles are reminiscent of short-range intermolecular interactions. Our methodology was used to assemble oppositely charged NPs into high-quality superlattices exhibiting Catalan shapes. This methodology can be applied to a wide range of charged nanoparticles of various sizes, shapes, and compositions. I will also discuss how electrostatic interactions can be used to assemble nanoparticles into transient assemblies, whose lifetime depends on and can be controlled by the availability of a small-molecule ionic “fuel”.