By Josh Perry, Editor
[email protected]

Scientists at Duke University (Durham, N.C.) proposed a new theory based on the separation of oil and vinegar in a vinaigrette for the assembly of nanoparticle structures with unique architectures, according to a report from the university.

This approach is depicted across the center of the image, while the resulting structures can be seen from different angles above and below. (Duke University)

This “oil-and-vinegar” approach would use a layer of liquids that refuse to mix together to force spherical nanoparticles to form single layers on the interface between the liquids. Rather than clumping together and forming random clusters, the scientists would be able to control the size of the layers by adding more or less of the particles that to each liquid.

“By altering this property along with others such as the nanoparticles’ composition and size, materials scientists can make all sorts of interesting shapes, from spindly molecule-like structures to zig-zag structures where only two nanoparticles touch at a time,” the article explained. “One could even imagine several different layers working together to arrange a system of nanoparticles.”

In the research paper, scientists described nanoparticles made of any material from gold to semiconductors to metallic elements and the substrates are modeled after polymers that can be used in specific applications.

The research was recently published in ACS Nano. The abstract stated:

“We propose a strategy for assembling spherical nanoparticles (NPs) into anisotropic architectures in a polymer matrix. The approach takes advantage of the interfacial tension between two mutually immiscible polymers forming a bilayer and differences in the compatibility of the two polymer layers with polymer grafts on particles to trap NPs within two-dimensional planes parallel to the interface.

“The ability to precisely tune the location of the entrapment planes via the NP grafting density, and to trap multiple interacting particles within distinct planes, can then be used to assemble NPs into unconventional arrangements near the interface. We carry out molecular dynamics simulations of polymer-grafted NPs in a polymer bilayer to demonstrate the viability of the proposed approach in both trapping NPs at tunable distances from the interface and assembling them into a variety of unusual nanostructures.

“We illustrate the assembly of NP clusters, such as dimers with tunable tilt relative to the interface and trimers with tunable bending angle, as well as anisotropic macroscopic phases, including serpentine and branched structures, ridged hexagonal monolayers, and square-ordered bilayers.

“We also develop a theoretical model to predict the preferred positions and free energies of NPs trapped at or near the interface that could help guide the design of polymer-grafted NPs for achieving target NP architectures.

“Overall, this work suggests that interfacial assembly of NPs could be a promising approach for fabricating next-generation polymer nanocomposites with potential applications in plasmonics, electronics, optics, and catalysis where precise arrangement of polymer-embedded NPs is required for function."