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A group of researchers from MIT developed a new class of small molecules that spontaneously assemble into nanoribbons stronger than steel.

The team says its surprising findings will likely be applicable for a wide variety of different use cases, including battery technology and water decontamination. Their findings were published on Jan. 21 in Nature Nanotechnology.


Secret sauce for self-assembly

The MIT group’s material is modeled after a cell membrane, the outer part of which is “hydrophilic,” meaning it is stable in water. The inner part, meanwhile, is “hydrophobic,” meaning it avoids water.

This is the secret sauce of the material, Julia Ortony, assistant professor in MIT’s Department of Materials Science and Engineering (DMSE), explains, as it “provides a driving force for self-assembly.”

The molecules orient themselves to lessen interactions between the hydrophobic part and water, leading them to take on a nanoscale shape.

Kevlar inspiration

The researchers then devised a way to stop the whole structure from collapsing when it dries, as would typically be the case.

One method for slowing down molecules, Ty Christoff-Tempesta, a Ph.D. student and first author of the paper, notes, “is to have them cling to each other more strongly than in biological systems.”

As Christoff-Tempesta explains, that can be accomplished via a dense network of strong hydrogen bonds joining the molecules together:

“That’s what gives a material like Kevlar — constructed of so-called ‘aramids’ — its chemical stability and strength,” he states in a press release.

‘Stronger than steel’

The team incorporated this idea into their design of a molecule with three main components: an outer portion that likes to interact with water, aramids in the middle for binding, and an inner part that has a strong aversion to water.

The researchers settled on a molecule that led to long ribbons with nanometer-scale thickness. When measuring the nanoribbons’ strength and stiffness after including Kevlar-style interactions between molecules and found that the nanoribbons were, surprisingly, stronger than steel.

The team says that they are still in the process of finding applications for their exciting new material, though it may be used to pull heavy metals, like lead or arsenic out of contaminated water, or used to greatly enhance the efficiency of electronic devices and batteries.

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