Self-Assembly of Poly(ethylene glycol)-Functionalized Gold Nanorods at the Vapor/Liquid Interface*

Using surface sensitive synchrotron X-ray diffraction, we report on the self-assembly of gold nanorods (AuNRs) into 2D films at the vapor/liquid interface. The films are facilitated by grafting the AuNRs with poly(ethylene glycol) (PEG). Grazing incidence small angle X-ray scattering (GISAXS) and specular X-ray reflectivity (XRR), show that PEG-AuNRs in aqueous suspensions migrate to the vapor/liquid interface in the presence of salt, forming a uniform monolayer with planar-to-surface orientation. Furthermore, the 2D assembled PEG functionalized AuNRs exhibit short range order into rectangular symmetry with side-by-side and tail-to-tail nearest-neighbor packing. The effect of PEG chain length and salt concentration on the 2D assembly are also reported.