This image shows the stringlike particles formed by iron (Fe) and nickel (Ni) and the more globular clusters formed by copper (Cu). Image: Abbaschian, Zachariah, et. al. 2021.In order for metal nanomaterials to deliver on their promise to energy and electronics, they need to shape up – literally.
To deliver reliable mechanical and electric properties, nanomaterials must have consistent, predictable shapes and surfaces, as well as scalable production techniques. Engineers at the University of California (UC) Riverside are meeting this challenge by vaporizing metals within a magnetic field to direct the reassembly of the metal atoms into predictable shapes. They report their work in a paper in the Journal of Physical Chemistry Letters.
Nanomaterials comprising particles measuring 1–100nm are typically created within a liquid matrix, which is expensive for bulk production and in many cases cannot produce nanoparticles made of pure metals, such as aluminum or magnesium. More economical production techniques typically involve vapor-phase approaches, in which a a cloud of particles condenses from a vapor, but they suffer from a lack of control.
Reza Abbaschian, professor of mechanical engineering, and Michael Zachariah, professor of chemical and environmental engineering, joined forces to develop a novel technique for creating nanomaterials from iron, copper and nickel in a gas phase. Their technique involves placing solid metal within a powerful electromagnetic levitation coil to heat the metal beyond its melting point, vaporizing it.
The resulting metal droplets levitate in the gas within the coil and move in directions determined by their inherent interactions with the magnetic forces. When the droplets bond, they do so in an orderly fashion that the researchers found could be predicted from the type of metal and how and where they applied the magnetic fields.
Iron and nickel nanoparticles formed string-like aggregates, while copper nanoparticles formed globular clusters. When deposited on a carbon film, the iron and nickel aggregates gave the film a porous surface, while the carbon aggregates gave it a more compact, solid surface. The qualities of the materials on the carbon film mirrored at larger scales the properties of each type of nanoparticle.
Because the magnetic field can be thought of as an 'add-on', this approach could be applied to any vapor-phase technique for generating nanomaterials where structure is important, such as the fillers used in polymer composites for magnetic shielding. It could also help to improve the electrical and mechanical properties of nanomaterials.
"This 'field directed' approach enables one to manipulate the assembly process and change the architecture of the resulting particles from high fractal dimension objects to lower dimension string-like structures. The field strength can be used to manipulate the extent of this arrangement," said Zachariah.
This story is adapted from material from the University of California, Riverside, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.