(510h) Many-Bodied Plasmon Ruler for Nanoparticle Dispersions and Assemblies

Self-assembly of plasmonic nanoparticles is a promising strategy for tuning the optical properties of soft materials through control of particle microstructure. A variety of complex plasmonic structures have been assembled experimentally, including nanoparticle clusters, superlattices, and gel networks, and system-specific electromagnetic simulations have connected each material’s optical response to their microstructural features. But, do the system-specific details matter, or are just a few key variables (e.g. overall or local nanoparticle density) enough to explain most observed optical features? Such generic, low-dimensional representations of structure/property relations would be incredibly useful for designing new plasmonic soft materials with desired optical properties. In this talk, we investigate the plasmonic properties of a simple thermodynamic model for colloidal nanoparticles – sticky hard spheres – which display an array of assembled states, including random dispersions, structured fluids, arrested colloidal gels, and ordered superlattices. We employ our recently developed mutual polarization method to obtain both macroscopic spectral features, e.g. optical extinction, as well as detailed microscopic information about the spatial and spectral distribution of electric field intensity and individual nanoparticle polarization moments. We use these data to establish many-bodied plasmon “rulers” expressing the colloidal material’s resonant frequency, linewidth, and near-field enhancement as functions of a small number of coarse-grained variables, the nanoparticle volume fraction, attraction strength, and surface-to-surface distance of closest approach. These plasmon rulers apply generically to a wide array of assembled structures and will aid in future design of soft optical materials.