Interfacial and Bulk Assembly of Anisotropic Gold Nanostructures: Implications for Photonics and Plasmonics

We report on the assembly of polymer-grafted nanostructures at the vapor/aqueous interface and in bulk solutions using synchrotron X-ray diffraction methods. Triangular- and octahedral-shaped gold nanostructures are synthesized and grafted with poly(ethylene glycol) (referred to as PEG-AuNTs and PEG-AuNOh, respectively), and their suspensions are manipulated with salts, (poly)electrolytes that induce interpolymer complexation and HCl to achieve organized assemblies. The assemblies at the vapor/liquid interface are explored by X-ray reflectivity and grazing-incidence small-angle X-ray scattering. Results show that PEG-AuNTs and PEG-AuNOh populate the interface, with some degree of orientation with respect to the liquid surface. The resulting assemblies can be tuned by the regulating electrolyte and pH levels of the suspensions. Similar suspension manipulations also induce three-dimensional assemblies that are revealed with solution small-angle X-ray scattering. In addition to controlling the three-dimensional (3D) aggregates by regulating the (poly)electrolytes and pH levels, we show that raising the temperature of the suspensions from 20 to above 50 °C induces and even improves the ordering of the assemblies. Our findings provide tools that can be used to assemble and orient anisotropic nanostructures for potential applications in photonics and plasmonics.