Controlling Coulomb Interactions Among Nanoparticles to Achieve Novel Assembly and Crystallization*

Controlling interactions among nanoparticles is paramount to achieving assemblies vital to technologies seeking to exploit their novel collective properties. Although various techniques have been advanced, robust ones are necessary for upscaling nanoparticle assembly and crystallization. Here, we show by grafting charge-end group (either -COOH or -NH₂) thiolated polyethylene glycol (PEG) to gold nanoparticles (AuNPs), the surface and total charge can be controlled by varying pH of the suspensions. Such control facilitates the formation of various exotic two- and three-dimensional ionic-like superstructures of oppositely charged binary constituents at the vapor/liquid interfaces or in bulk. Using surface-sensitive synchrotron-based X-ray diffraction at grazing angles of incidence (GISAXS), X-ray reflectivity (XR), and SAXS, we establish the formation of distinct checker-board square and hexagonal lattice structures in 2D and two different body-centered cubic lattices in 3D. In this talk, we will discuss X-ray diffraction and electron microscopy results and novel analytical techniques to explain the results.