2018 MRS FALL MEETING: Symposium BM08: Materials-to-Devices for Integrated Wearable Systems—Energy Harvesting and Storage, Sensors/Actuators and Integration
Svetlana Boriskina, Massachusetts Institute of Technology
Wearable Fabrics for Passive Heating and Cooling - Can Polyethylene Do Both?
Written by Daniel Gregory
Fabrics provide a key additional layer that helps to regulate human body heat. In extreme environments, current clothing options are typically either very bulky, cool passively using moisture wicking from sweat, or have poorly integrated elaborate active cooling systems. Svetlana Boriskina explored the ability of polyethylene to provide both active and passive cooling effects. Polyethylene was chosen due to its low absorption of near-infrared wavelengths, emitted for radiative cooling in humans. Other textile fabrics usually absorb strongly in this region, and so are unable to let heat escape to cool properly, or reflect the heat back to the wearer, though metals can be added for this reflection.
The challenge with polyethylene is to make it visible in the near infrared yet opaque at visible wavelengths. To do this, Boriskina explained how she and her group were able to create fibers with diameters roughly equal to the wavelength of visible light but thinner than infrared radiation, causing a scattering effect that provided the visible light opacity. This was further demonstrated through infrared and visible camera comparisons. Polyethylene processed in several different ways was then compared to metallized emergency blankets and unprotected bare skin analogue in their ability to insulate heat given off by a surface and also keep that surface cool under sunlight. It was shown that powerful heating or cooling effects depended on the processing method, with knitted polyethylene outperforming the emergency blanket in thermal insulation while nanoporous polyethylene was the most effective cooling fabric, and showed promise as a material for thermal camouflage. Boriskina presented tests of moisture wicking and drying time, showing surprisingly that knitted polyethyelene performed best despite the polymer usually being hydrophobic. The material was also shown to have many other properties such as its light weight and the ability to be processed into fabric on conventional equipment and in a range of colors, as well as already having a well-established recycling procedure.