Fabrication and Optical Properties of Polymer-Grafted Gold Nanorod Assemblies

Precise, large-scale assembly of polymer-grafted nanoparticles (PGNs) has shown great promise for the scalable manufacturing of sensors, energy storage devices, and photonic elements. Different than traditional ligand-coated nanoparticles, PGNs are stabilized by high molecular weight polymers at relatively low grafting densities. In this regard, PGNs behave as soft colloids, possessing favorable processing properties typical of polymer systems while still retaining the ability to pack into ordered structures. Herein, we demonstrate that large scale, highly uniform monolayer films of gold-polystyrene nanorods can be fabricated from PGN inks within a few seconds using a simple flow-coating technique. Using a combination of AFM, SEM, and GISAXS, we observe nanorod positional and orientational order dependent on coupling between processing conditions, polymer canopy, and surface energy. Additionally, optical extinction measurements reveal strong plasmonic coupling between the gold nanorods which can systematically be tuned by varying film morphology. With fundamental understanding of structure-processing relationships, we demonstrate optical notch filters using laser-induced reshaping of resonant nanoparticle subpoulations.