Harvard SEAS scientists have created a new lightweight, multifunctional nanofiber material to protect its wearers from extreme temperatures and ballistic threats.
Developed in collaboration with the U.S. Army, the new material could be a boon to soldiers, astronauts, firefighters and other first responders.
Most American combat casualties are caused by explosions and not gunshot wounds as it is generally perceived.
The U.S. Army has thus been developing protective equipment that come with multiple layers of different materials. This however results in a bulky, heavy gear.
As pointed out by senior author and Harvard SEAS professor Kit Parker, the three primary tasks for soldiers on the battlefield are to move, shoot, and communicate.
If you limit one of those, you decrease survivability and you endanger mission success, says Parker.
“Our goal was to design a multifunctional material that could protect someone working in an extreme environment, such as an astronaut, firefighter or soldier, from the many different threats they face,” points out first author and postdoc Grant M. Gonzalez.
The scientists had to first explore the trade-off between mechanical protection and thermal insulation.
Materials such as metals and ceramics, have a highly ordered and aligned molecular structure. This allows them to withstand and distribute the energy of a direct blow.
Insulating materials, on the other hand, have a much less ordered structure, which prevents the transmission of heat through the material.
Woven Kevlar, for example, has a highly aligned crystalline structure and is used in protective bulletproof vests.
Porous Kevlar aerogels, on the other hand, have been shown to have high thermal insulation.
“Our idea was to use this Kevlar polymer to combine the woven, ordered structure of fibers with the porosity of aerogels to make long, continuous fibers with porous spacing in between,” said Gonzalez.
“In this system, the long fibers could resist a mechanical impact while the pores would limit heat diffusion.”
The research team used immersion Rotary Jet-Spinning (iRJS), a technique developed by Parker’s Disease Biophysics Group, to manufacture the fibers.
In this technique, a liquid polymer solution is loaded into a reservoir and pushed out through a tiny opening by centrifugal force as the device spins.
When the polymer solution shoots out of the reservoir, it first passes through an area of open air, where the polymers elongate and the chains align.
Then the solution hits a liquid bath that removes the solvent and precipitates the polymers to form solid fibers.
Since the bath is also spinning – like water in a salad spinner – the nanofibers follow the stream of the vortex and wrap around a rotating collector at the base of the device.
By tuning the viscosity of the liquid polymer solution, the researchers were able to spin long, aligned nanofibers into porous sheets.
These sheets provide enough order to protect against projectiles but enough disorder to protect against heat.
Image and content: Grant Gonzalez/Harvard SEAS