The conditioner and the fan are they really the only solution to the scorching heat and summer heat waves? Researchers at the University Pritzker School of Molecular Engineering of Chicago have found another way. The research group has developed a new material which manages to break down the temperature of the wearer. This material is a multilayer that starts with a polymer base and can therefore take on different shapes, a bit like plastic. For this reason it can find application in various fields, not only for clothing but also for food preservation, to prevent cars from overheating and for insulation in buildings. Among the various shapes it can take, it can also be transformed into textile fiberso we can get a tissue to be used for our clothes or for seat covers in cars.
How the new material works
The design of the new material aims to mitigate the effect of the urban heat islands, where the perceived heat comes from the Sunfrom the cement and from surrounding buildingsThe challenge is therefore to produce a material with two property optics: high reflectance from the radiation solar and reduction of the absorption heat from the environment (infrared rays).
The result is this: a multilayer of different materials which, when put together, are able to reflect solar radiation on one side and reduce heat absorption on the other.
How the new temperature-reducing material is made
The materials used are, from outside to inside:
- a polymer layer in polymethylpentene (PMP) which selectively reflects radiation infrared solar;
- an intermediate layer of silver nanowires which reflects incoming thermal radiation;
- one last one wool in contact with the skin which serves to move heat from the skin to the intermediate layer.
Outer layer: PMP
This layer must issue heat selectively in the required wavelength range. Among all the materials the most suitable is the PMP polymer, polymethylpentene.
To make this polymer spinnable, theelectrospinninga technique that allows to obtain fibers with extremely small diameters, from micrometers to a few nanometers. First the polymer is dissolved in a solvent, then extruded into fibers and then into micro fibersThe latter are deposited to create the first layer of fabric.
Middle layer: nsilver anophiles
The PMP could not be in contact with human skin alone, otherwise it would have absorbed the thermal radiation, compromising the entire emission. For this reason, a second layer was needed and silver was chosen as the material, excellent conductor. In fact, we find a lager of silver nanowires, which is a kind of net one-dimensional and hyper-thin silver. This is also deposited behind the PMP with spray coating.
Inner layer: wool
Finally, a layer of woolwithout which the heat emitted by the skin would be reflex from the silver layer inside the air gap between skin and fabric, blocking the heat exchange between body and fabric. Wool can also be replaced by other natural fabricsbut in general we know that wool alone is an excellent thermal insulator, thanks to its flake structure.
What are the first results obtained: up to 6.2 °C less than the ambient temperature
The result of these layered materials creates a fabric with double optical property. It has a high emissivity in the required wavelength range (8-13 µm), which allows it to emit heat into outer space. At the same time, it reflects – i.e. has low absorbency – in another wavelength range, which minimizes heat absorption from the surrounding space.
After a series of digital simulations, the researchers conducted some experiments with samples of the prototype. Positioned horizontally and vertically, the samples of the new fabric are respectively 2.3 °C And 6.2 °C cooler than room temperature.
The fabric was also tested on a radiator to simulate the effect on a human body and the experiment recorded a temperature of 2.6°C less than cotton. A volunteer tested the fabric on his forearm and the temperature difference between the new fabric and the cotton was found to be 1.8 °C.
All that remains is to continue with the experiments, testing them in an urban scenario.
Possible future developments
The material is spinnable and, once transformed into fabric, also has good mechanical properties and is wearable and washable.
Called SSHF (=Selective Hierarchical Fabricor “spectrally selective hierarchical tissue”), is currently pending a patent.
Especially in the current context of global warming, projects like this take on great importance because they create a way to reduce temperatures without using electricity, as is the case with air conditioners or fans. In this case, in fact, we are talking about passive cooling.
