Plasmonic Ruler at the Liquid–Liquid Interface

Abstract

We report on a simple, fast, and inexpensive method to study adsorption and desorption of metallic nanoparticles at a liquid/liquid interface. These interfaces provide an ideal platform for the formation of two-dimensional monolayers of nanoparticles, as they form spontaneously, cannot be broken, and are defectcorrecting, acting as 2D 'nanoparticle traps'. Such two-dimensional self-assembled nanoparticle arrays have a vast range of potential applications in displays, catalysis, plasmonic rulers, optoelectronics, sensors and detectors. Here, we show that 16 nm diameter gold nanoparticles can be controllably adsorbed to a water/1,2-dichloroethane interface, and we can direct the average inter-particle spacing at the interface over the range 6-35 nm. The particle density and average inter-particle spacing are experimentally assessed by measuring the optical plasmonic response of the nanoparticles in the bulk and at the interface, and by comparing the experimental data with existing theoretical results.Keywords: liquid-liquid interface, Plasmonic Ruler, Nanoparticles, Self Assembly, Centrifugation. Nanoparticle (NP) adsorption at liquid-liquid interfaces (LLI) is a well established phenomenon that was first reported independently more than a century ago by Ramsden and Pickering. 1, 2 More recently, plasmonic NPs at LLIs have been reported to possess novel "metal liquid like" properties 3 that have sparked a renewed interest. Driven by the growing need for cheap, fast and reproducible bottom-up assembly for nanotechnological applications, the unique optical, 4 magnetic, 5 electrical 6 and chemical 7 properties of such films has attracted intensive research in a rapidly growing field.NP assemblies at LLIs hold great promise in diverse fields ranging from electrovariable optics 8 to templates for hierarchical self assembly, 9 and plasmonic rulers. 10 One of the main benefits of localising NPs at a LLI for these applications is the aforementioned self-assembly. 11 Currently, most technological applications of nanoassemblies are based around solid-state fabrication. Although the control that the solid interface offers is unparalleled, it does have several drawbacks when compared to a LLI. One such drawback is topological defects -these can be introduced either during or post-manufacturing and are extremely difficult to correct. In fact it is often easier to fabricate a new device rather than attempting to repair defects. Conversely, a LLI system has the ability to self-correct without any external manipulation. 12 An additional drawback of a solid state system becomes clear when introducing the exciting concept of a plasmonic ruler. [13][14][15] The coupling between excitations of localized plasmons in NPs can allow for precise spatial information. This concept has been demonstrated between 2D arrays, 10 particle dimers 14 at solid interfaces and tethered NPs in bulk solution. 16 It has even been recently demonstrated to provide 3-dimensional structural information. 17 The use of plasmonic particles at the LLI sh...

Interactions and Stress Relaxation in Monolayers of Soft Nanoparticles at Fluid-Fluid Interfaces

“…Ligand-grafted metal or semiconductor nanocrystals at fluid-fluid interfaces are widely used in nanomaterials synthesis [13][14][15] and in catalytic processes [16]. Simulation studies predict the rearrangement of the ligand brush into anisotropic lensshaped configurations when these nanoparticles adsorb at fluid-fluid interfaces [4][5][6]8].…”

Gold Nanofilm Redox Catalysis for Oxygen Reduction at Soft Interfaces

“…Recently, biphasic O 2 reduction has been achieved under neutral and alkaline conditions [17]. Therein, the ET reduction of organic solubilised O 2 was facilitated by IT of hydrated metal cations (M + ) across the soft interface (see equations (3) and (4)). …”

“…An interface between two immiscible electrolyte solutions (ITIES) or a "soft" interface is an attractive platform at which to assemble nanoparticles (NPs) due to its electrochemical polarisability, inherent defect-free nature, mechanical flexibility and the ease with which NPs may be manipulated and precisely tuned therein [1][2][3][4][5][6][7][8]. A burgeoning area of research is concerned with the biphasic electrocatalysis of redox reactions of interest for energy research, including the oxygen (O 2 ) reduction reaction (ORR) [9][10][11][12][13][14][15][16][17][18][19] and the hydrogen (H 2 ) evolution reaction (HER) [20][21][22][23][24][25][26][27][28], using soft interfaces functionalized with molecular species, metallic NPs or inorganic non-precious metal-based materials.…”

Interfacial Redox Catalysis on Gold Nanofilms at Soft Interfaces

“…Since Reincke and co-workers 24 reported the spontaneous self-assembly of AuNPs at a water | heptane interface following the addition of alcohol, numerous alternative approaches have been described to trigger the assembly of metallic NPs at soft interfaces. 15,25,26 The alcohol injection method is still one of the most convenient but requires introducing a substantial volume of alcohol (at least 10 vol %) 27À29 close to the interface and lacks a precise control of the interfacial surface coverage of AuNPs in the film. The redox properties of metallic NPs, and by extension their self-assembled 2D films, depend directly, but not exclusively, on the excess charge present on the metallic NP.…”