Engineers weave state-of-the-art fabric that can cool and warm the wearer

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Textile engineers have developed a fabric woven from ultra-fine nano-yarns composed in part of phase-change materials and other advanced substances that combine to produce a fabric that can respond to temperature changes to heat and cool its carrier as needed. .

Materials scientists have designed an advanced textile with nanoscale yarns containing a phase-change material in their core that can store and release large amounts of heat as the material changes phase from liquid to solid. By combining the yarns with electrothermal and photothermal coatings that enhance the effect, they essentially developed a fabric that can both quickly cool the wearer and warm them up when conditions change.

An article describing the manufacturing technique appeared in the journal American Chemical Society ACS Nano August 10.

Many professions, from firefighters to farm workers, involve harsh hot or cold environments. Cold stores, ice rinks, steel forges, bakeries and many other job sites require workers to make frequent transitions between different and sometimes extreme temperatures. Such regular temperature changes are not only uncomfortable, but can also cause illness or even injury, and require a constant change of bulky clothes. A sweater will keep a worker warm in a cold meat locker, but could overheat the same worker when leaving that space.

One option for relieving heat or cold stress for these workers, or anyone else, from athletes to travelers, who experience such discomfort, is the emerging technology of personal thermal management textiles. These tissues can directly manage the temperature of localized areas around the body.

These fabrics often use phase change materials (PCM) which can store and then release large amounts of heat as the material changes phase (or state of matter, for example, from solid to liquid).

One of these materials is paraffin, which can in principle be incorporated into a textile material in various ways. When the temperature of the environment around paraffin reaches its melting point, its physical state changes from solid to liquid, which involves heat absorption. Then the heat is released when the temperature reaches the freezing point of paraffin.

Unfortunately, the inherently strong rigidity of PCMs in their solid form and leakage when liquid have so far hampered their application in the portable thermal control field. A number of different strategies, including microencapsulation (in which PCM such as paraffin is embedded in extremely small capsules), have been attempted to improve “packaging efficiency” to overcome stiffness issues. and leak.

“The problem here is that the manufacturing methods for phase-change microcapsules are complex and very expensive,” said Hideaki Morikawa, corresponding author of the paper and an advanced textile engineer at the Institute of Fiber Engineering at the Institute. Shinshu University. “Worse still, this option provides insufficient flexibility for any realistic portable application.”

So the researchers turned to an option called coaxial electrospinning. Electrospinning is a method of manufacturing extremely fine fibers with diameters in the nanometer range. When a polymer solution contained in a bulk reservoir, typically a syringe with a needle tip, is connected to a high voltage power source, an electrical charge builds up on the surface of the liquid. Soon a point is reached where the electrostatic repulsion of the accumulated charge is greater than the surface tension and this results in an extremely fine jet of the liquid. As the jet of liquid dries in flight, it is further elongated by that same electrostatic repulsion that gave rise to the jet, and the resulting ultrafine fiber is then collected on a drum.

Coaxial electrospinning is much the same, but involves two or more polymer solutions fed from neighboring spinnerets, allowing the production of coated or hollow nanofibers. These core and sheath fibers are similar in structure to the coaxial cable one might use on their home stereo, but are much, much smaller.

In this case, the researchers encapsulated the PCM in the center of the electrospun nanofiber to solve the PCM leakage problem. In addition, the ultra-fine fibers allow extremely favorable flexibility suitable for human clothing.

To further extend the range of work environments where the textile would work, and the accuracy of thermal regulation, the researchers paired the PCM material with two other personal thermal regulation technologies.

The combination of photosensitive materials – those that react to the presence of solar energy – with PCMs potentially offers the possibility of further increasing the energy storage capacity of the textile. Additionally, coating the composite material with polymers that convert electricity to heat (an electrothermal conductive coating) can offset a similar expansion of energy storage if the worker is in cloudy, rainy, or indoor conditions. .

The researchers combined the three options – PCM, carbon nanotubes and polydopamine solar absorbers, and electroconductive poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (known as ‘PEDOT:PSS’) polymers – into one ‘ trimode ‘thermoregulating and wearable textile.

This multi-core and shell structure enables synergistic cooperation between its various components and provides on-demand thermal regulation that can adapt to a wide range of environmental temperature changes.

The researchers now aim to further improve the phase transition properties of the fabric and develop practical and portable applications for their material.

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