Tuning Hierarchical Order and Plasmonic Coupling of Large-Area, Polymer-Grafted Gold Nanorod Assemblies via Flow-Coating

Abstract

Solution-based printing of anisotropic nanostructures is foundational to many emerging technologies, such as energy storage devices, photonic elements, and sensors. Methods to rapidly (>mm/s) manufacture large area assemblies (≫cm2) with simultaneous control of thickness (<10 nm), nanoparticle spacing (<5 nm), surface roughness (<5 nm), and global and local orientational order are still lacking. Herein, we demonstrate such capability using flow-coating to fabricate robust, self-supporting mono- and bilayer films of polystyrene-grafted gold nanorods (PS-AuNRs) onto solid substrates. The relationship among solvent evaporation, deposition speed, substrate surface energy, concentration, and film thickness for solutions of such hairy hybrid nanoparticles spans the Landau–Levich and evaporative film formation regimes. In the Landau–Levich regime, solvent evaporation rapidly concentrates the PS-AuNRs, leading to the formation of thin films with distinct, randomized side-by-side domains. Alternatively, processing at slower velocities in the evaporative regime results in the global alignment of PS-AuNRs. Processing speed and substrate surface energy afford tuning of the film’s optical extinction of a given PS-AuNR via fine control of inter-rod distance and subsequent plasmonic coupling between neighboring nanorods. Because the concept of the polymer-grafted nanorod can be expanded to a variety of different polymer canopies, shapes, and core materials, the processing–structure relationships established in this work will have important implications on the future development of anisotropic nanostructure-based applications.

Plasmon-Mediated Chiroptical Second Harmonic Generation from Seemingly Achiral Gold Nanorods

“…The Stokes parameters were also analyzed to determine the purity, or degree of polarization, of the harmonic field. For pure light polarization states, either linear or circular, S 0 2 = S 1 2 + S 2 2 + S 3 2 , whereas mixed polarization states yield S 0 2 > S 1 2 + S 2 2 + S 3 2 . Hence, a nonzero difference between S 0 2 and the summation over the remaining Stokes parameters indicates the harmonic wave is a superposition of polarization states.…”

“…Indeed, changes in metal–metal atom bond lengths on the subangstrom scale are known to induce large second-order responses in 2-D metals . Most commonly, gold nanorods are formed in solution by silver-ion-assisted, seed-mediated synthesis that utilizes cationic surfactants, such as cetyltrimethylammonium bromide (CTAB). − Although this approach typically yields single-crystalline nanorods, the final structures are characterized by rounded or faceted tips and an overall asymmetric shape when viewed at the atomic level . Scanning transmission electron microscopy (STEM) images of several gold nanorods used in this study are shown in Figures A and S1A.…”

“…For pure light polarization states, either linear or circular, S 0 2 = S 1 2 + S 2 2 + S 3 2 , whereas mixed polarization states yield S 0 2 > S 1 2 + S 2 2 + S 3 2 . 27 Hence, a nonzero difference between S 0 2 and the summation over the remaining Stokes parameters indicates the harmonic wave is a superposition of polarization states. The resultant degree of polarization, DOP, for the harmonic signal is calculated as .…”

Supplementary document for Towards maximum optical efficiency of ensembles of colloidal nanorods - 5830321.pdf

“…The AuNRs were prepared according to the scale up protocol. 2,3 The growth solution was prepared by mixing HAuCl 4 (500 µL, 0.1 M), AgNO 3 (500 µL, 0.1 M), CTAB (0.1g). Next, hydroquinone (1.25 ml, 0.1M) was added to the growth solution as a mild reducing agent.…”

Coexistence and Phase Behavior of Solvent–Polystyrene-Grafted Gold Nanoparticle Systems

“…The appeal of PGNs stems from their tunability, where the design modularity of the nanoparticle core (size, geometry, and composition) and polymer canopy (graft density, composition, and molecular weight) prescribe their properties, processability, and interparticle potential. , As with stars and other architected macromolecules, PGNs bridge the gap between colloids and linear chains. , Due to the irreversibility of chain grafting and the range of composition, shape, and size, PGNs are expected to exhibit a rich array of phase behavior within the canopy, among nearest neighbors, as well as with respect to the shape of the assembly. For example, the polymer-grafted canopy has been shown to exhibit micro-phase separation in response to solvent and temperature. , Additionally, finite clusters of spherical PGNs exhibit directionally dependent interparticle potential due to the deformability of the grafted canopy .…”