Breathable clothing is important for soldiers looking to avoid heat stress and exhaustion, but in some situations, added protection is needed against biological and chemical agents. Current protective equipment struggles to effectively offer both at once, but now scientists at Lawrence Livermore National Laboratory (LLNL) have developed a material that begins to bridge the gap, using carbon nanotubes to actively block contaminants while still allowing water vapor to escape.
The material is a flexible polymer membrane containing an array of aligned carbon nanotubes (CNTs), which function as extremely tiny pores. The key to how they block biological agents is simple: these tubes have a diameter of under 5 nanometers, which is 5,000 times smaller than a human hair, and crucially, less than half the size of most bacteria and viruses. Sweat, in the form of water vapor, can easily escape from the wearer's skin through these pores, yet bacteria are just too big to get in.
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"We demonstrated that these membranes provide rates of water vapor transport that surpass those of commercial breathable fabrics like GoreTex, even though the CNT pores are only a few nanometers wide," says Ngoc Bui, the lead author of the paper.
During filtration tests, the nanotube membranes were exposed to liquid solutions containing dengue virus and successfully kept the bugs out, even when the material was wet.
Chemical agents, on the other hand, pose more of a challenge. Particles are smaller, so size exclusion alone won't work. Instead, the team is modifying the surface of the material with groups of atoms that sense chemical threats and respond by closing the pores. Another possibility is having the material's surface peel off in response to contact with chemicals, similar to how living skin reacts.
"The material will be like a smart second skin that responds to the environment," says Kuang Jen Wu, another author of the study. "In this way, the fabric will be able to block chemical agents such as sulfur mustard (blister agent), GD and VX nerve agents, toxins such as staphylococcal enterotoxin and biological spores such as anthrax."
The team is now working on speeding up the material's transition between its breathable and protective states, with swatch-level tests beginning in early 2018. It says that uniforms made from the material could be in the field within a decade.
The research was published in the journal, Advanced Materials, and the team discusses the project in the video below.