Ramathasan Thevamaran, a UW–Madison assistant professor of engineering physics who led the research, said the nanofibre mats exhibit protective properties that far surpass other material systems at much lighter weight.
Thevamaran and his collaborators detailed the advance in a paper published in ACS Nano.
To create the material, Thevamaran and postdoctoral researcher Jizhe Cai mixed multi-walled carbon nanotubes with Kevlar nanofibres. The resulting nanofibre mats are said to be superior at dissipating energy from the impact of tiny projectiles moving faster than the speed of sound.
The advance lays the groundwork for carbon nanotube use in lightweight, high-performance armour materials such as bulletproof vests or in shields around spacecraft to mitigate damage from flying high-speed microdebris.
“Nano-fibrous materials are very attractive for protective applications because nanoscale fibres have outstanding strength, toughness, and stiffness compared to macroscale fibres,” Thevamaran said in a statement. “Carbon nanotube mats have shown the best energy absorption so far, and we wanted to see if we could further improve their performance.”
The team synthesised Kevlar nanofibres and incorporated a tiny amount of them into their carbon nanotube mats, which created hydrogen bonds between the fibres. Those hydrogen bonds modified the interactions between the nanofibres and, along with just the right mixture of Kevlar nanofibres and carbon nanotubes, caused a leap in the overall material’s 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 nanofibre mat. When we modified the interfacial interactions in our mats by adding Kevlar nanofibres, we were able to achieve nearly 100 per cent improvement in energy dissipation performance at certain supersonic impact velocities.”
The researchers tested their new material using a laser-induced microprojectile impact testing system in Thevamaran’s lab. One of only a handful like it in the United States, the system uses lasers to shoot micro-bullets into the material samples.
“Our system is designed such that we can actually pick a single bullet under a microscope and shoot it against the target in a very controlled way, with a very controlled velocity that can be varied from 100 metres per second all the way to over 1km per second,” Thevamaran said. “This allowed us to conduct experiments at a time scale where we could observe the material’s response — as the hydrogen bond interactions happen.”
The new nanofibre material is also stable at very high and very low temperatures, making it useful for applications in a wide range of extreme environments.
The researchers are patenting their nanofibre material through the Wisconsin Alumni Research Foundation.