“People who are skiing or hiking in colder weather usually wear layers so they can adjust how much heat their clothing is trapping as their body heats up,” said Po-Chun Hsu, assistant professor of mechanical engineering and materials science at Duke.
Strategically placing patches of a material that can let out heat when a person is sweating, results in making a one-piece-fits-all textile.
When attempting to make such a dual-purpose material, scientists turned to nylon. It is inexpensive, lightweight, soft, and if cut into flaps, nylon curls in on itself a little bit when one side is exposed to moisture.
However, Nylon is not known for making particularly warm clothing, so they added a layer of heat-trapping silver on top.
Expecting the weight of the silver to bog down the nylon flaps, the layer was kept as thin as possible. But to their surprise, the silver addition made the flaps curl back even more.
After experimenting with various thicknesses of silver, scientists discovered a Goldilocks spot around 50 nanometers, which is 2,000 times thinner than a sheet of paper.
Any thinner and the phenomena would not be as strong. Any thicker and the weight of the silver started interfering with the vents opening.
Scientists explained this confusing finding that when the bottom layer of nylon gets wet, it wants to expand like a sheet being pulled from its sides since it is attached to the silver on top, it cannot stretch in those directions.
The easiest option remaining is for the two-layer material to curl up, allowing the nylon to expand while forcing the silver to shrink. Then researchers created a patch about the size of a human hand with flaps about the size of a fingernail.
Compared with an average traditional textile represented by a blend of polyester and spandex, the material is about 16% warmer when dry with the flaps closed and 14% cooler when humid with the flaps open.
This approach has advantages to existing methods of venting heat through warm clothing, such as placing zippers beneath the armpits. The sweating parts of the body need to be vented, which is not necessarily the underarms.
Scientists are working on making the vents as small as possible while retaining their effectiveness. They are also exploring using a top nanocomposite layer that could make the material any color without changing its thermal attributes.
Source: Medindia
