Engineers at the University of California, Irvine, have made a new and improved space blanket that allows users to control their temperature. The blanket, inspired by the adaptive properties of cephalopod skin, comprises a soft and stretchable polymer matrix that is transparent to infrared radiation covered with an array of infrared-deflecting metal domains anchored within the matrix.
Reflecting infrared radiation (heat) is important for many technologies, including electronic circuits, aircraft and spacecraft components, hospital warming devices, building insulation and speciality textiles and clothing. The drawback to most infrared-deflecting materials, however, is that they are static and unable to respond and adapt to changing environmental conditions. Although some adaptive systems have been developed, they are relatively expensive, energy inefficient and cumbersome.
Among passive thermal management systems, the “space blanket”, developed by NASA in the 1960s, is one of the most well-known. It generally consists of a plastic sheet overlaid with a thin continuous layer of metal such as aluminium. This hybrid structure, which has remained fundamentally unchanged since its conception, is very efficient at reflecting infrared radiation. It is thus routinely employed, in its various forms, in applications such as packaging and emergency covering. Athletes also use it as a protective shield that prevents them from losing too much body heat after a race.
Inspiration from the colour-changing skin of coleoid cephalopods
A team led by Alon Gorodetsky has now taken inspiration from the dynamic colour-changing skin of coleoid cephalopods (squid, octopuses and cuttlefish) to make a new version of the classic space blanket. Squid skin, for example, consists of multiple layers, one of which contains embedded chromatophore organs that are packed with pigment granules. These cells can be switched by the muscle cells in between them to contract and expand from minute points to flattened disks, thereby changing the wavelengths of light that they absorb and reflect.
Gorodetsky and colleagues used a similar concept in their work and designed a composite thermoregulatory material made up of a soft and stretchable infrared-transparent polymer matrix covered with an array of infrared-deflecting metal domains stably anchored within the matrix via column-like nanostructures.
“In our design, the polymer matrix emulates the chromatophore-containing transparent dermal layer of squid, while the metal domains emulate the embedded chromatophore organs themselves,” explain the researchers.
In the relaxed state, the metal domains are densely packed and completely cover the underlying matrix in a way that is similar to how the expanded plate-like chromatophores overlap in squid skin. In this configuration, the materials reflect nearly all incoming infrared radiation. When stretched, however, the anchored metal domains move apart and uncover parts of the underlying polymer matrix – just like the contracted point-like chromatophores distance themselves from each other in squid skin. The material thus transmits a large part of the incident infrared radiation – again, in the same way that arrays of contacted chromatophores transmit much more visible light.
Promising properties and possible applications
The researchers say that their material boasts an on/off switching ratio of around 25 for light transmittance. It is also capable of regulating a heat flux of around 36 W/m2 with a mechanical power input of just 3 W/m2. Finally, it can manage a quarter of the heat produced by a person at rest (their metabolic heat flux) and can modulate changes in the wearer’s body temperature by nearly 10-fold in real time. This means that it might be integrated into more advanced personal thermal management systems that are electrically or electromechanically actuated.
The material might find use in a host of applications, both traditional and emerging ones, says Gorodetsky. These include: reflective insulating inserts in buildings that adapt to different environmental conditions; tents that would help keep occupants at a comfortable temperature outdoors; and coatings to effectively manage the temperature of electronic components. Conformable electronic skin and untethered soft robots may also benefit.
Octopus skin inspires new infrared reflector
Clothing would be a particularly fitting application for the new, bio-inspired material, he adds. Indeed, the team is already collaborating with athletic clothing manufacturer Under Armour Inc.
“The temperature at which people are comfortable in an office is slightly different for everyone. Where one person might be fine at 70 degrees, the person at the next desk over might prefer 75 degrees,” he says. “Our invention could lead to clothing that adjusts to suit the comfort of each person indoors. This could result in potential savings of 30 to 40 percent on heating and air conditioning energy use.”
The research is detailed in Nature Communications.
