Interfacial and Bulk Assembly of Anisotropic Gold Nanostructures: Implications for Photonics and Plasmonics

Abstract

We report on the assembly of polymer-grafted nanostructures at the vapor/aqueous interface and in bulk solutions using synchrotron X-ray diffraction methods. Triangular-and octahedral-shaped gold nanostructures are synthesized and grafted with poly(ethylene glycol) (referred to as PEG-AuNTs and PEG-AuNOh, respectively), and their suspensions are manipulated with salts, (poly)electrolytes that induce interpolymer complexation and HCl to achieve organized assemblies. The assemblies at the vapor/liquid interface are explored by X-ray reflectivity and grazing-incidence small-angle X-ray scattering. Results show that PEG-AuNTs and PEG-AuNOh populate the interface, with some degree of orientation with respect to the liquid surface. The resulting assemblies can be tuned by the regulating electrolyte and pH levels of the suspensions. Similar suspension manipulations also induce three-dimensional assemblies that are revealed with solution small-angle X-ray scattering. In addition to controlling the three-dimensional (3D) aggregates by regulating the (poly)electrolytes and pH levels, we show that raising the temperature of the suspensions from 20 to above 50 degrees C induces and even improves the ordering of the assemblies. Our findings provide tools that can be used to assemble and orient anisotropic nanostructures for potential applications in photonics and plasmonics.

Distinct thermoresponsive behaviour of oligo- and poly-ethylene glycol protected gold nanoparticles in concentrated salt solutions

“…However, they do not induce 3D assembly into supercrystals. 26 Different strategies that include salt concentration, interpolymer complexation, pH and temperature changes demonstrate that the self-assembly of structures other than spheres is also possible as it has been observed for gold nanorods 29 and gold nanotriangles 30 grafted with an EGn polymer corona. In this work, we present a study of the stability of EGn-AuNPs formed with methoxy-terminated oligo-or poly-ethylene glycol of different chain length (Scheme 1).…”

“…22 Moreover, the steric hindrance generated by the reorganization of flexible hydrophilic polymer brushes during interparticle association is critical for the morphological selectivity in the assembly. 23 Taking advantage of the hydrophobic/hydrophilic tuneable characteristics of the PEG polymers depending on the experimental conditions, Vaknin et al have dedicate great efforts to elucidate the influence of different salt concentrations [24][25][26][27][28] and temperature of the suspensions [29][30][31] in the interfacial assembly of EGn-AuNPs. The addition of ions to the solution impinges a poor solvent character for the polymers that could provoke the self-assembly of the EGn-AuNPs and its phase separation.…”

Effect of Polymer Chain Length on the Superlattice Assembly of Functionalized Gold Nanoparticles

“…Recently, we have demonstrated the assembly and crystallization of gold nanoparticles (AuNPs) grafted with water-soluble polymers, such as polyethylene glycol (PEG) and poly­( N -isopropylacrylamide). − By adding salt to the PEG-grafted AuNP suspensions, two-dimensional (2D) superlattices are formed at the liquid/vapor interface. , At sufficiently high salt concentrations, three-dimensional (3D) crystalline aggregates are formed in the bulk, which partially precipitate out from the solution. , At moderate salt concentrations, raising the temperature from 20 to 80 °C and subsequent temperature heating–cooling cycling induces spontaneous crystallization. − Longer chains are required to achieve a NIR; , however, the use of relatively long chain polymers adds new levels of complexity. The challenges are twofold.…”

“…16−24 By adding salt to the PEGgrafted AuNP suspensions, two-dimensional (2D) superlattices are formed at the liquid/vapor interface. 23,25 At sufficiently high salt concentrations, three-dimensional (3D) crystalline aggregates are formed in the bulk, which partially precipitate out from the solution. 24,26 At moderate salt concentrations, raising the temperature from 20 to 80 °C and subsequent temperature heating−cooling cycling induces spontaneous crystallization.…”

Symmetric and asymmetric overgrowth of a Ag shell onto gold nanorods assisted by Pt pre-deposition

“…The longitudinal LSPR of AuNRs can be simply tuned by the aspect ratio (length/diameter) of the AuNR, from the visible (∼600 nm) to the near infrared region (>1200 nm). Thus, AuNRs have shown great promise in optical devices, 8 biological sensing, 9 photochemistry, 10 photonics, 11 catalysis, 12,13 and surface-enhanced Raman spectroscopy (SERS). 14,15 In recent years, overgrowth of a second metal on AuNRs, such as Pt, Pd, and Ag (named AuNR–M afterwards, M = Pt, Pd, or Ag), have been extensively studied.…”