As bulletproof materials prove their importance on the battlefield once in the ongoing battle between Ukraine and Russia, a group of scientists has forged a material made of nanotubes , which outperforms Kevlar and steel with its unique chemical properties.

When working on bullet-proof materials, researchers consider the weight of the material as a key subject in order to keep the armored units mobile while keeping them safe.

A team of engineers from the University of Wisconsin-Madison has forged a new ultralight armor material called “nanofiber mat”.

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The new form is based on tiny cylinders of carbon that are at the same thickness as a single atom. This new material, called carbon nanotubes, has shown promise as the next-generation material in various fields, such as in the fight against climate change or in saving lives.

The authors of the study used multi-walled carbon nanotubes and combined them with Kevlar nanofibers to create a new bullet-proof material. Carbon nanotubes were used in the study as they have demonstrated impact absorbing properties in earlier research.

“Nano-fibrous materials are very attractive for protective applications because nanoscale fibers have outstanding strength, toughness, and stiffness compared to macroscale fibers,” says Ramathasan Thevamaran a UW–Madison assistant professor of engineering physics, who led the research. “Carbon nanotube mats have shown the best energy absorption so far, and we wanted to see if we could further improve their performance.”

Upon finding out about the absorption properties of carbon nanotubes, the team of scientists turned to chemistry. Incorporating the right ratio of Kevlar nanofibers and “nanofiber mats” made up of carbon nanotubes they have managed to produce hydrogen bonds between fibers, which resulted in a dramatic leap in performance. 

“The hydrogen bond is a dynamic bond, which means it can continuously break and re-form again, allowing it to dissipate a high amount of energy through this dynamic process,” Thevamaran said. “In addition, hydrogen bonds provide more stiffness to that interaction, which strengthens and stiffens the nanofiber mat. When we modified the interfacial interactions in our mats by adding Kevlar nanofibers, we were able to achieve nearly 100 percent improvement in energy dissipation performance at certain supersonic impact velocities.”

The new material was tested with a microprojectile impact testing system, which launches micro bullets at varying speeds at materials. The test results showed that the new material is more protective against high-speed impacts than Kevlar or steel plates.

The researchers estimate that the material has the potential to allow spacecraft to absorb impacts from high-speed space debris.

Achieving extreme dynamic performance in nanofibrous materials requires synergistic exploitation of intrinsic nanofiber properties and inter-fiber interactions. Regardless of the superior intrinsic stiffness and strength of carbon nanotubes (CNTs), the weak nature of van der Waals interactions limits the CNT mats from achieving greater performance. We present an efficient approach to augment the inter-fiber interactions by introducing aramid nanofiber (ANF) links between CNTs, which forms stronger and reconfigurable interfacial hydrogen bonds and π–π stacking interactions, leading to synergistic performance improvement with failure retardation. Under supersonic impacts, strengthened interactions in CNT mats enhance their specific energy absorption up to 3.6 MJ/kg, which outperforms widely used bulk Kevlar-fiber-based protective materials. The distinct response time scales of hydrogen bond breaking and reformation at ultrahigh-strain-rate (∼107–108  s–1) deformations additionally manifest a strain-rate-dependent dynamic performance enhancement. Our findings show the potential of nanofiber mats augmented with interfacial dynamic bonds─such as the hydrogen bonds─as low-density structural materials with superior specific properties and high-temperature stability for extreme engineering applications.