A Method for Promoting Assembly of Metallic and Nonmetallic Nanoparticles into Interfacial Monolayer Films

Abstract

Two-dimensional metal nanoparticle arrays are normally constructed at liquid-oil interfaces by modifying the surfaces of the constituent nanoparticles so that they self-assemble. Here we present a general and facile new approach for promoting such interfacial assembly without any surface modification. The method use salts that have hydrophobic ions of opposite charge to the nanoparticles, which sit in the oil layer and thus reduce the Coulombic repulsion between the particles in the organic phase, allowing the particles to sit in close proximity to each other at the interface. The advantage of this method is that because it does not require the surface of the particles to be modified it allows nonmetallic particles including TiO2 and SiO2 to be assembled into dense interfacial layers using the same procedure as is used for metallic particles. This opens up a route to a new family of nanostructured functional materials.

Rapid One‐Pot Preparation of Large Freestanding Nanoparticle‐Polymer Films

“…An elegant method of obtaining NP 2D arrays is through spontaneous self‐assembly at liquid–liquid interfaces to form metal liquid‐like films (MeLLFs). These are densely packed monolayers of metal NPs self‐assembled at the interface between two immiscible liquids, which can be obtained simply by shaking a non‐water‐miscible organic solvent with a portion of aqueous metal colloid in the presence of a low concentration of a chemical compound (a “promoter” or “modifier”) which promotes particle adsorption at the interface . These mobile arrays have the same characteristics as the best of the deposited NP films in that they are densely packed, electronically coupled monolayers of particles which can readily be prepared on the cm 2 scale at room temperature in minutes with no specialist equipment.…”

“…Figure illustrates the fabrication process: Initially a mixture of metal colloid and a polystyrene/dichloromethane (DCM) solution was shaken vigorously in the presence of a promoter in a hydrophobic container to form a lustrous and mobile film of NPs at the liquid–liquid interface (Figure a,b). The promoter, which consists of a hydrophobic cation, stabilizes the negatively charged NPs at the liquid‐liquid interface by providing charge‐screening . A hydrophobic container was used so that the DCM wrapped around the aqueous layer, meaning that the MeLLF partly sat at the top surface of the liquid–liquid interface (Figure c).…”

Self‐Assembly of Nanoparticles in 2D and 3D: Recent Advances and Future Trends

“…Comparing the results of both in situ atomic force microscopy and grazing incidence X‐ray small‐angle scattering, it is revealed that the average density of the nanoparticles at the interface varies with the concentration of the surfactant and the interaction between the tip and interface can be studied for the local determination of the acting interfacial interactions. Bell and co‐authors have presented a new approach for promoting 2D interfacial assembly of metal nanoparticles via the utilization of salts that possess oppositely charged hydrophobic ions to that of the nanoparticles residing at the organic layer. As a result, the coulombic repulsion between the particles in the oil phase is reduced that renders the particles to remain in close proximity to the interface.…”

Surface‐Enhanced Raman Spectroscopy for the Detection of a Metabolic Product in the Headspace Above Live Bacterial Cultures

“…In situ SERS monitoring of the headspace above the cultures used a SERS substrate composed of a densely‐packed monolayer of dry Ag or Au particles deposited onto a quartz window from a metal‐like liquid film created by assembling the particles at a water/dichloromethane interface . Data on characterisation of the Ag and Au substrates can be found in the Supporting Information (Figure S1).…”