(543b) Three-Phase Self-Assembly of Gold Nanoparticle Monolayers – Overcoming Ligand Size Limitations
A simple yet effective technique was developed to prepare centimeter-scale monolayer gold nanoparticle (Au NP) films of long-range order with hydrophobic ligands. Aqueous Au NPs were entrapped at an oil/water interface where the Au NP surface could be modified with various types of amine-terminated ligands, including alkanes and polystyrene. The Au NPs then spontaneously translocated to an air/water interface to form a monolayer film. The spontaneous formation of an Au NP film at an air/water interface was due to the minimization of the system Helmholtz free energy. The self-assembled Au NP films are of a hexagonal close packed structure. The interparticle center-to-center space was dictated by the amine ligand length. These Au NP monolayers exhibit tunable surface plasma resonance and excellent spacial homogeneity for surface-enhanced Raman-scattering. The â??air/water/oilâ? self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to scale up the manufacture of plasmonic nanoparticle devices with precisely designed optical properties.