Researchers gain control over internal structure of self-assembled composite materials

January 15, 2020

CHAMPAIGN, Ill. -- Composites made from self-assembling inorganic materials are valued for their unique strength and thermal, optical and magnetic properties. However, because self-assembly can be difficult to control, the structures formed can be highly disordered, leading to defects during large-scale production. Researchers at the University of Illinois and the University of Michigan have developed a templating technique that instills greater order and gives rise to new 3D structures in a special class of materials, called eutectics, to form new, high-performance materials.

The findings of the collaborative study are published in the journal Nature.

Eutectic materials contain elements and compounds that have different melting and solidification temperatures. When combined, however, the composite formed has single melting and freezing temperatures - like when salt and water combined to form brine, which freezes at a lower temperature than water or salt alone, the researchers said. When a eutectic liquid solidifies, the individual components separate, forming a cohesive structure - most commonly in a layered form. The fact that eutectic materials self-assemble into composites makes them highly desirable to many modern technologies, ranging from high-performance turbine blades to solder alloys.

"Having a single melting point has advantages in composite materials processing," said Paul Braun, a professor of materials science and engineering and director of the Materials Research Lab at the U. of I., who led the project. "Instead of depositing layers of material individually, we start with a liquid that self-assembles as it solidifies. This can speed up production and allows us to make larger volumes at one time."

However, self-assembly can lead to problems, he said, as its uncontrolled nature can form defects.

"Templating is a common practice used in organic polymers processing," said Ashish Kulkarni, an Illinois graduate student and the first author of the study. "However, it is not something that has been explored in inorganic materials processing because inorganic microstructures are more rigid and harder to control."

To demonstrate this process in the lab, the team built templates with tiny posts arranged in hexagonal shapes to control the resolidification of a melt containing silver chloride and potassium chloride - a eutectic material that naturally forms layers as it cools.

"If not controlled, the only microstructures this system will form are layers," said Katsuyo Thornton, a professor of materials science and engineering at Michigan, who conducted computer simulations with graduate student Erik Hanson, both of whom are study co-authors. "We can vary the cooling rate to make the layers thicker or thinner, but the pattern stays the same. By adding a template that the liquid solidifies around, we hoped new patterns would emerge."

The team found that as the silver and potassium chloride melt to solidify around the hexagonal-shaped templates, the posts get in the way of the layer formation and produce a composite with an array of different square, triangular and honeycomb-shaped microstructures instead - the specifics of structure depending on the distance between the posts on the template.

"The repeating nature of these templates and newly formed structures reduces the chances for defects to form," Braun said. "So, not only did we form exciting new microstructures, but we also reduced the number of defects in the resulting composite material."

The researchers will explore how the new microstructures influence the physical properties of a wide range of eutectic materials.

"The materials we used in our experiments are transparent, so the first direction to head in might be to explore optical materials, and there is a lot of potential in the area of photonic crystals," Braun said. "We're still a long way from real application, but the possibilities are abundant."
-end-
Braun also is affiliated with the department of chemistry, the department of mechanical science and engineering, the Holonyak Micro & Nanotechnology Lab and the Beckman Institute for Advanced Science and Technology at the U. of I.

This research was supported by the Air Force Office of Scientific Research.

Editor's notes:

To reach Paul Braun, call 217-244-7293; email pbraun@illinois.edu.

The paper "Archimedean lattices emerge in template directed eutectic solidification" is available online and from the U. of I. News Bureau. DOI: 10.1038/s41586-019-1893-9

University of Illinois at Urbana-Champaign, News Bureau

Related Magnetic Properties Articles from Brightsurf:

Scientists design magnets with outstanding properties
An international team of researchers led by the Centre de Recherche Paul Pascal (UMR 5031, CNRS -University of Bordeaux) has discovered a novel way to design magnets with outstanding physical properties, which could make them complementary to, or even competitive with traditional inorganic magnets, which are widely used in everyday appliances.

Topology gets magnetic: The new wave of topological magnetic materials
The electronic structure of nonmagnetic crystals can be classified by complete theories of band topology, reminiscent of a 'topological periodic table.' However, such a classification for magnetic materials has so far been elusive, and hence very few magnetic topological materials have been discovered to date.

Bridging the gap between the magnetic and electronic properties of topological insulators
Scientists at Tokyo Institute of Technology shed light on the relationship between the magnetic properties of topological insulators and their electronic band structure.

Nano-microscope gives first direct observation of the magnetic properties of 2D materials
Widefield nitrogen-vacancy microscope solves problem of there being no way to tell exactly how strongly magnetic a 2D material was.

Spintronics: Researchers show how to make non-magnetic materials magnetic
A complex process can modify non-magnetic oxide materials in such a way to make them magnetic.

Probing the properties of magnetic quasi-particles
Researchers have for the first time measured a fundamental property of magnets called magnon polarisation -- and in the process, are making progress towards building low-energy devices.

Manipulating non-magnetic atoms in a chromium halide enables tuning of magnetic properties
The magnetic properties of a chromium halide can be tuned by manipulating the non-magnetic atoms in the material, a team, led by Boston College researchers, reports in the most recent edition of ScienceAdvances.

Turmeric could have antiviral properties
Curcumin, a natural compound found in the spice turmeric, could help eliminate certain viruses, research has found.

Elucidating how asymmetry confers chemical properties
New research by Carnegie's Olivier Gagné and collaborator Frank Hawthorne of the University of Manitoba categorizes the causes of structural asymmetry, some surprising, which underpin useful properties of crystals, including ferroelectricity, photoluminescence, and photovoltaic ability.

Coupled magnetic materials show interesting properties for quantum applications
In a new study led by the US Department of Energy's Argonne National Laboratory, researchers have uncovered a novel way in which the excitations of magnetic spins in two different thin films can be strongly coupled to each other through their common interface.

Read More: Magnetic Properties News and Magnetic Properties Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.