The chain-mail-like material is exceptionally flexible and strong. It could be used for body armor, among other things.
The illustration shows how X-shaped monomers are linked together to create the first mechanically interlocking 2-D polymer. Similar to chain mail, the material exhibits exceptional strength.
Mark Seniw, Center for Regenerative Nanomedicine, Northwestern University
A team from Northwestern University in the US state of Illinois has developed the first two-dimensional material with mechanical interlocking. The nanoscale polymer resembles the interlocking links of a chain maille and is said to have exceptional flexibility and strength. According to the university, the material contains 100 trillion mechanical bonds per square centimeter – the highest density of mechanical bonds ever achieved. Possible uses include body armor, as well as other applications requiring lightweight, flexible, and robust materials.
“We have created a completely new polymer structure,” says Prof. William Dichtel, co-author of the study published in the Journal Science on January 17. Because each of the mechanical bonds has leeway, the structure cannot tear easily. “If you pull on it, it can dissipate the force in multiple directions. And if you want to tear it, you would have to break it in many, many different places. We are continuing to explore its properties and will probably study it for years to come,” says Dichtel.
New Process Led to the Goal
For many years, researchers had tried to develop mechanically interlocked molecules with polymers. But it was nearly impossible to get polymers to form mechanical bonds. That's why Dichtel's team took a new approach. They started with X-shaped monomers – the building blocks of polymers – and arranged them in a specific crystalline structure. They then reacted the crystals with another molecule to create bonds between the molecules within the crystal.
The resulting crystals consist of numerous layers of 2-D interlocking polymer sheets. Within these, the ends of the X-shaped monomers are connected to the ends of other X-shaped monomers. Then, more monomers are threaded through the spaces. Despite its rigid structure, the polymer is “surprisingly flexible,” according to the report.
Material can be Produced in Large Quantities
Dichtel's team also found that the layers of interlocking monomers peel away from each other when the polymer is dissolved. “Once the polymer is formed, there's not much holding the structure together,” Dichtel said. “So when we put it in a solvent, the crystal dissolves, but each 2-D layer holds together. We can manipulate those individual layers.”
The researchers produced 0.5 kg of the material and expect that even larger quantities will be possible once the most promising applications emerge. Previous polymers with mechanical bonds were usually produced in very small quantities using methods that are unlikely to be scalable.
Inspired by the inherent strength of the material, Dichtel's team at Duke University, led by Prof. Matthew Becker, added it to Ultem. Ultem is an amorphous polyimide, belongs to the same family as Kevlar and has high structural strength. It can withstand extreme temperatures as well as acidic and caustic chemicals. The researchers developed a composite material made of 97.5% Ultem fibers and only 2.5% of the 2-D polymer. This small percentage is said to have “significantly increased” the overall strength and toughness of Ultem.
Dichtel expects that the new polymer could have a future as a specialty material for lightweight body armor and ballistic fabrics: “We still have a lot of analysis to do, but we can say that it improves the strength of these composites.”
This is a partly automated translation of this german article.