This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
WASHINGTON, D.C. — Soldiers can’t achieve peak performance when they’re chilled to the bone. So in winter weather, some soldiers may don up to seven layers of clothing. That much fabric can weigh them down. Later, soldiers might find themselves overdressed, now getting hot and sweaty. That sweat, in turn, can turn to ice if the weather is super cold. But it doesn't have to. Researchers have just come up with a way to lighten a winter warrior’s load and fight the threat of frozen sweat.
They’ve designed a new high-performance fabric. It could become the basis of underwear for troops deployed in places blasted by Arctic cold. Scientists unveiled it here, last August, at the fall meeting of the American Chemical Society.
Paola D’Angelo is a bioengineer. She uses principles of biology to solve problems. Elizabeth Hirst is a chemist. Both work at the U.S. Army Natick Soldier Research, Development and Engineering Center in Massachusetts. Their team got the initial idea for this innovation from some earlier work by a group at Stanford University in California. Their new fabric improves on that earlier research. It also adds an important new twist.
Yi Cui and Po-Chun Hsu are materials scientists at Stanford University. Their team already had been using metal nanowires to create see-through electrical conductors. Such materials could be handy for things such as thinner smartphones, displays on car windshields and more. Teeny, tiny nanowires have diameters at the scale of billionths of a meter.
At Cui’s suggestion, the Stanford team set out to use conductive nanowires in a fabric. It would be “warm, lightweight and breathable,” explains Hsu. That way, it could help reduce the energy needed for indoor heating.
The team got itty bitty wires of silver to form a mesh across cotton fabric. The silvery metal can reflect body heat back to someone’s skin. The treated fabric also can carry an electrical current. So, batteries could deliver extra heat when needed. Cui’s team described its work two years ago in Nano Letters.
Now the Army’s team has been tweaking that idea to work not just with cotton, but also with high-performance fabrics. Athletes, soldiers and others often turn to such fabrics when they’re doing things that call for lots of physical activity or that expose them to extreme conditions.
Examples of these special fabrics include polyester, nylon and other synthetic fabrics. Their fibers are engineered by people, instead of coming from natural materials, such as plant fibers or animal hair. The Army uses synthetic fabrics (or blends that include synthetics) for gloves, socks and a soldier’s base layer. That’s the “underwear” that sits closest to the skin. And it's for that layer that this team has been building upon the Stanford group’s work.
Besides getting the concept to work with other fabrics, the Army researchers tested the ability of such fabrics to hold up through repeated washings. And their fabric indeed performed well.
In addition, the Army team packed more fibers onto each area of fabric than the Stanford team had. That denser wire mesh can carry more current and provide more warmth. Three volts of electricity is enough to warm a test swatch that’s 6.45 square centimeters (1-square-inch) in one minute by 56 degrees Celsius (100 degrees Fahrenheit), D’Angelo reports. A typical watch battery is all that’s needed to provide those 3 volts.
Soldiers won’t want their underwear that hot. But the fabric could provide quick heat in a hurry. With the right controls, soldiers could even customize how warm their clothes get.
Super soakers for sweat
That material would still not be a perfect solution for working in cold weather, however. Even if it were used under with the Army’s current winter wear, soldiers can get sweaty as they hike, climb or carry out other tasks. That’s because the synthetic fabric of the base layer is not good at wicking away moisture, Hirst explains. Instead, sweat soaks into the fabric. As water in the sweat cools, it can ice up. That’s “obviously very uncomfortable,” she adds.
To deal with this, her team is working with hydrogel beads. A hydrogel is a type of “super soaker” material that can absorb a lot of water. In this case, the beads can sop up as much as 40 times their weight in water, Hirst says. The molecules of the beads are made from polymers. These are long chains of identical repeating units. A part of each unit in the hydrogel has a segment that attracts water.
Researchers could tweak the hydrogel to act differently at different temperatures, Hirst points out. As a soldier sweats, the fabric would warm. That warming could lead the hydrogel to soak up any sweat, moving moisture away from the skin. Later, when the soldier took off the underwear, it would cool down. Moisture in the hydrogel beads could then evaporate into the air. Now the fabric would be ready to wear again.
Don’t expect to see the new fabric on soldiers just yet. “We are in the basic research stages,” Hirst says. Among other things, her team will play with different ways to attach the hydrogel beads to the wired fabric. Her group also wants to work on a protective coating for the nanowires. That would help the silver resist tarnishing, which could reduce its reflectiveness.
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“We look forward to seeing their cloth combining silver nanowire and hydrogel together,” says Hsu. In his view, it makes good sense to combine features that would provide both heating and cooling as needed. “In the future stages of this research,” he suspects, “there might be some trade-off between the total amount of heating and cooling that the cloth can provide versus its compactness and weight.”
In addition to developing better winter underwear, the Army team hopes the new fabric might lead to warmer gloves and socks. After lots and lots of field testing by soldiers, the fabric might find its way into civilian clothes, too. Then anyone could wear it for skiing, winter walks, snowboarding or other cold-weather fun.
The outdoor temperature topped 32º C (90º F) when the researchers unveiled their new fabric in Washington, D.C. Few folks at the meeting were ready for winter. Later, however, many might appreciate that some scientists and engineers had been thinking ahead.
basic research Research performed to gain a general understanding of how things work, and not with any particular application in mind. This type of work is contrasted with applied research, which is work done to accomplish a particular purpose — such as to cure disease, make a building stronger or make a fuel burn cleaner.
battery A device that can convert chemical energy into electrical energy.
bioengineer Someone who applies engineering to solve problems in biology or in systems that will use living organisms.
biology The study of living things. The scientists who study them are known as biologists.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
conductive Able to carry an electric current.
conductor (in physics and engineering) A material through which an electrical current can flow.
current A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of electricity moving through some point over a particular period of time.
diameter The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.
electricity A flow of charge, usually from the movement of negatively charged particles, called electrons.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
engineering The field of research that uses math and science to solve practical problems.
evaporate To turn from liquid into vapor.
fabric Any flexible material that is woven, knitted or can be fused into a sheet by heat.
fiber Something whose shape resembles a thread or filament. (in nutrition) Components of many fibrous plant-based foods. These so-called non-digestible fibers tend to come from cellulose, lignin, and pectin — all plant constituents that resist breakdown by the body’s digestive enzymes.
field An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.
hydrogel A “smart” material that can change its structure in response to its environment, such as the local temperature, pH, salt or water concentration. The material is made from a polymer — a chain made from links of identical units — that have free, water-attracting ends sticking out. So in the presence of water, it may hold (bond) those water molecules for quite a while. Some hydrogels are used in baby diapers to hold urine, in potting soils to hold water near to plants until they need it and in wound dressings to keep a sore from drying out.
innovation (v. to innovate; adj. innovative) An adaptation or improvement to an existing idea, process or product that is new, clever, more effective or more practical.
materials science The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.
metal Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure).
moisture Small amounts of water present in the air, as vapor. It can also be present as a liquid, such as water droplets condensed on the inside of a window, or dampness present in clothing or soil.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
nano A prefix indicating a billionth. In the metric system of measurements, it’s often used as an abbreviation to refer to objects that are a billionth of a meter long or in diameter.
nanowire A wire or rod on the order of a billionth of a meter in cross-section or in circumference. It is usually made from some type of semiconducting material. However some bacteria make string-like anchoring structures on the same size scale. Like the semiconductor wire, the bacterial ones also can transport electrons.
nylon A silky material that is made from long, manufactured molecules called polymers. These are long chains of atoms linked together.
polyester A synthetic material used chiefly to make fabrics. The actual chemical name for the material used is polyethylene terephthalate.
polymer A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).
synthetic An adjective that describes something that did not arise naturally, but was instead created by people. Many synthetic materials have been developed to stand in for natural materials, such as synthetic rubber, synthetic diamond or a synthetic hormone. Some may even have a chemical makeup and structure identical to the original.
weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.
Meeting: P. D’Angelo et al. Wearable personal thermal management through silver nanowire-coated textiles. American Chemical Society 2017 fall meeting. August 20, 2017. Washington, D.C.
Meeting: E. Hirst et al. Effect of extreme cold treatment on morphology and behavior of hydrogel microparticles. American Chemical Society 2017 fall meeting. August 20, 2017. Washington, D.C.
Journal: P. Hsu et al. Personal thermal management by nanowire-coated textile. Nano Letters, Vol. 15, January 14, 2015, p. 365. doi: 10.1021/nl5036572.