Coherent Plasmon-Exciton Coupling in Silver Platelet-J-aggregate Nanocomposites

Hybrid nanostructures that couple plasmon and exciton resonances generate hybridized energy states, called plexcitons, which may result in unusual light-matter interactions. We report the formation of a transparency dip in the visible spectra of colloidal suspensions containing silver nanoplatelets and a cyanine dye, 1,1′-diethyl-2,2′-cyanine iodide (PIC). PIC was electrostatically adsorbed onto the surface of silver nanoplatelet core particles, forming an outer J-aggregate shell. This core–shell architecture provided a framework for coupling the plasmon resonance of the silver nanoplatelet core with the exciton resonance of the J-aggregate shell. The sizes and aspect ratios of the silver nanoplatelets were controlled to ensure the overlap of the plasmon and exciton resonances. As a measure of the plasmon-exciton coupling strength in the system, the experimentally observed transparency dips correspond to a Rabi splitting energy of 207 meV, among the highest reported for colloidal nanoparticles. The optical properties of the silver platelet-J-aggregate nanocomposites were supported numerically and analytically by the boundary-element method and temporal coupled-mode theory, respectively. Our theoretical predictions and experimental results confirm the presence of a transparency dip for the silver nanoplatelet core J-aggregate shell structures. Additionally, the numerical and analytical calculations indicate that the observed transparencies are dominated by the coupling of absorptive resonances, as opposed to the coupling of scattering resonances. Hence, we describe the suppressed extinction in this study as an induced transparency rather than a Fano resonance.United States. Army (Basic Research Program)United States. Army Edgewood Chemical Biological CenterUnited States. Army Research Office. Institute for Soldier Nanotechnologies (Contract No. W911NF-13-D-0001

Ionomers for Tunable Softening of Thermoplastic Polyurethane

Thermoplastic polyurethane (TPU) sulfonate ionomers with quaternary ammonium cations were synthesized to achieve soft TPUs without using conventional low molecular weight plasticizers. The sulfonated monomer <i>N</i>,<i>N</i>-bis­(2-hydroxy­ethyl)-2-amino­ethane­sulfonic acid (BES) neutralized with bulky ammonium counterions was incorporated as a chain extender to internally plasticize the TPU. Increasing the steric bulk of the counterion and the concentration of the ionic species produced softer TPUs with improved melt processability. The incorporation of the sulfonate species suppressed crystallinity of the TPU hard block, which was mainly responsible for the softening of the polymer. The synthetic procedure developed allows for facile tuning of the mechanical properties of the TPU by simply switching the counterion and/or increasing the feed ratio of ionic monomer. The precursors in this study were synthesized and analyzed via ¹H NMR, and the thermomechanical properties of the resulting TPU ionomers were characterized by differential scanning calorimetry, dynamic mechanical analysis, Shore A hardness, and static mechanical testing

Tuning Optical Properties of Plasmonic Aerosols through Ligand–Solvent Interactions

Plasmonic nanoparticles are highly tunable light-harvesting materials with a wide array of applications in photonics and catalysis. More recently, there has been interest in using aerosolized plasmonic nanoparticles for cloud formation, airborne photocatalysts, and molecular sensors, all of which take advantage of the large scattering cross sections and the ability of these particles to support intense local field enhancement (“hot spots”). While extensive research has investigated properties of plasmonic particles in the solution phase, surfaces, and films, aerosolized plasmonics are relatively unexplored. Here, we demonstrate how the capping ligand, suspension solvent, and atomization conditions used for aerosol generation control the steady-state optical properties of aerosolized Silica@Au plasmonic nanoshells. Our experimental results, supported with spectral simulations, illustrate that ligand coverage and atomization conditions control the degree of solvent retention and thus the spectral characteristics and potential access to surfaces for catalysis in the aerosol phase, opening a new regime for tunable applications of plasmonic metamaterials

Fabrication of Anisotropic Silver Nanoplatelets on the Surface of TiO2 Fibers for Enhanced Photocatalysis of a Chemical Warfare Agent Simulant, Methyl Paraoxon

Among the world’s most deadly toxins are a class of organophosphates that are used as chemical warfare agents (CWAs). It is imperative to continue to develop novel means for mitigation and protection against these chemical threats. Sensitizing the surface of metal oxide semiconductors with plasmonic nanoparticles for photocatalytic degradation of chemical threats has been a prominent area of research in recent years. Anisotropic silver nanoplateles were purposefully grown on the surface of TiO2 fibers, in order to determine the impact of silver nanoparticle shape on (1) the generation of hot electrons by the silver, (2) the subsequent transfer of those electrons from the silver into the TiO2, and (3) the photocatalytic behavior of the Ag−TiO2 composite. To elucidate the charge injection properties of the composites, transient absorption experiments (pump−probe experiments) were undertaken. These involved pumping the composite samples with a range of discrete visible wavelengths and probing the composite within the intraband transitions of the TiO2. As a complement to these experiments, the photocatalytic properties of the Ag−TiO2 composite fibers were studied via the photocatalytic hydrolysis of methyl paraoxon, a chemical warfare agent simulant. This involved exposure of the methyl paraoxon to either red, green, blue, or white LED illumination. For both the transient absorption and photocatalytic experiments, maximum efficiency was observed for those scenarios in which the resonance of the silver platelets most closely matched the wavelength of incident radiation. Furthermore, the composite with silver nanoplatelets clearly outperformed its counterpart with silver nanospheres, in terms of both charge injection and photocatalytic behavior. We believe these results shall serve as a basis for future catalytic research in which the resonance of anisotropic plasmonic nanoparticles (in a given composite) shall be designed to match the wavelength of incident radiation