Think of armor as light as cloth but stronger than steel, made from materials that interlock like molecular chainmail. Scientists may have just taken the first step in making this a reality.

A team of researchers led by Northwestern University scientists has created what may be the first two-dimensional (2D) mechanically interlocked material, similar to chainmail links. The material, detailed in a January 16 study published in the journal Scienceis exceptionally flexible and strong, with promising applications in products such as lightweight body armor and ballistic fabric.

The researchers built the material at the nanoscale level, meaning its individual components can be measured in nanometers. This is technically a polymer: a substance made of large molecules, which are themselves composed of smaller chemical units called monomers. Examples of polymers include proteins, cellulose, and nucleic acids.

A 2D mechanically interlocked material is a polymer structure that uses mechanical bonds—bonds with physical interlocking, as opposed to, for example, covalent bonds, which often consist of polymers and involve the sharing of electrons. The material has 100 trillion mechanical bonds per 0.16 square inch (1 square centimeter), which is the highest density of mechanical bonds ever created, according to the researchers.

“We created a completely new polymer structure,” said study co-author William Dichtel of Northwestern University in a university statement. “It’s like chainmail in that it doesn’t break easily because each of the mechanical links has a little freedom to slide around. If you pull it, it can dissipate the applied force in many directions. And if you want to break it down, you have to break it down in many, many different places. We’ve been exploring its properties and probably studying it for years.”

The biggest challenge in making mechanically interlocked molecules lies in figuring out how to guide the polymers to form mechanical bonds. Madison Bardot of Northwestern University, who led the study, is credited with developing a new method to achieve this. The team put x-shaped monomers into a crystal structure (a specific ordered arrangement) and reacted the crystals with another molecule. This reaction creates mechanical bonds within the crystals. The final product is 2D layers of interlocked polymer sheets made of these bonds between X-shaped monomers, whose gaps the researchers filled with more X-shaped monomers.

“This is a high-risk, high-reward idea where we have to question our assumptions about what kinds of reactions are possible in molecular crystals,” Dichtel said. The resulting material is extremely strong, but still flexible and easy to manipulate, because the individual sheets of interlocked molecules are separated from each other when the polymer is dissolved in a solvent.

“After the polymer is formed, there is not a whole lot that holds the structure together,” he added. “So, when we put it in a solvent, the crystal dissolves, but each 2D layer holds together. We can manipulate individual sheets. “

While previous researchers have made mechanically bound polymers in very small quantities that are difficult to mass produce, the team’s new method is surprisingly scalable. They produced more than a pound (0.5 kg) of material, and suggested the possibility of producing more.

Even a small percentage of the new polymer structure, however, can improve other components. The researchers made a material composed of 97.5% Ultem fiber (an extremely tough material in the same family as Kevlar) and 2.5% of 2D polymer, and concluded that the mixture made the former significantly stronger. on.

“We still have a lot of analysis to do, but we can say that it improves the strength of these composite materials,” continued Dichtel. “Almost every property we measure is unique in some way.”

This incredibly strong and flexible material may be the armor of the future.