In case a football helmet withstands an impact severe enough to cause the wearer a concussion, chances are the safety features of the helmet are compromised, making it no longer safe for reuse. But engineers at Michigan State University (MSU) have recently developed a liquid nanofoam lining they claim can help helmets sustain repeated impacts, increasing their longevity and improving their protective features.
The new material is packed with tiny pores whose tiny diameters are nanometers in size, creating a significantly large surface area. “The whole area of MSU’s Spartan Stadium could be folded up into one gram of nanofoam,” explains Weiyi Lu, an MSU assistant professor of civil and environmental engineering.
In normal conditions, the material is rigid, and adding liquid to it would fill its pores. But the scientists overcame this problem by coating the material with a hydrophobic substance, preventing the material from absorbing liquid. As a result, the saltwater liquid inside the nanofoam becomes pressurized during an impact.
“When the pressure reaches the safety threshold, ions and water are forced into the nanopores making the material deformable for effective protection. In addition, the liquid-like material is pliable enough to form into any shape,” explains Lu. “Helmets are pretty much one shape but the liquid nanofoam material can be made to fit a person’s specific head shape or profile.”
In experiments, the scientists tested the eighth-inch liquid nanofoam liner alongside the three-quarter-inch piece of solid foam traditionally used in helmets. While both materials deformed after being struck with the same amount of force, the liquid nanofoam recovered between the continuous impacts of the test, which wasn’t the case for the solid foam.
“The liquid nanofoam outperformed the solid foam,” Lu says. “The nanofoam was able to mitigate continuous multiple impacts without damage; the results were identical from test one through test 10.”
The scientists behind the research envision the novel material finding use beyond football and military helmets. According to them, the liquid nanofoam could one day also be used in passive safety devices such as automobile airbags and bumpers, as well as making buildings more resilient in the face of earthquakes.