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Polar Bear Inspired, Energy-efficient Building Insulation

Scientists have designed a nature-inspired carbon tube aerogel thermal insulating material based upon the microstructure of polar bear hair. This lightweight, highly-elastic and more efficient heat insulator opens up new avenues for energy-efficient building insulation


 
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Polar bear hair helps the animal to prevent heat loss in cold and humid climatic conditions in the frigid Arctic circle. Polar bear hair is naturally hollow unlike human hair or other mammals. Each hair strand has a long, cylindrical core running through its center. It is this shape and spacing of the cavities which gives polar bear hair the distinct white coat. These cavities have multitude of properties like exceptional heat-holding, water resistance, elasticity etc. which makes them a very good thermal insulator material. The hollow centers restrict movement of heat while design-wise making every strand extremely lightweight. Also, the non-wettable nature of polar bear hair keeps the animal warm when they are swimming in sub-zero temperatures and also under humid conditions. Polar bear hair is thus a very good model for designing synthetic materials which can provide efficient insulation from heat just like polar bear hair does it naturally.

In a new study published on June 6 in Chem, scientists have developed a novel insulator taking inspiration from and mimicking the microstructure of individual polar bear hairs and hence acquiring all of its unique properties. They fabricated millions of super-elastic, lightweight hollowed-out carbon tubes, each the size of a single hair strand and wound these into an aerogel block. The design process first started with making cable hydrogel from tellurium (Te) nanowires as a template which was coated with a carbon shell. Then they fabricated a carbon tube aerogel (CTA) from this hydrogel by first drying it and next calcinating it in an argon inert atmosphere at 900 °C to remove Te nanowires. This unique design makes CTA an excellent thermal insulator and also super-elastic in nature as it rebound at the speed of 1434 mm/s. This is the fastest ever compared to all conventional elastic materials. Authors point out that it is even more elastic than polar bear hair.

Due to the hollow structure of carbon tubes, the material exhibits excellent thermal conductivity which is lower than that of dry air owing to the material's inner diameter being less than of free path of air. The material showed longevity by maintaining its thermal conductivity after being stored for 3 months at room temperature with 56% relative humidity. The CTA is lightweight with density of 8 kg/m3; lighter than majority of available thermal insulator materials. It doesn’t get affected by water as it is non-wettable. Also, the mechanical structure of the CTA is maintained even after numerous compress-release cycles at different strains.

The current study describes a new carbon tube aerogel - inspired from polar-bear hair’s hollow tube design - which acts as an excellent thermal insulator. Compared to other aerogel insulation materials available, this polar-bear inspired hollow-tube design is light in weight, more resistant to heat flow, water proof and doesn’t degrade over its lifetime.

Improved and more efficient thermal insulation systems hold promise for conserving primary energy consumption. Energy is now in short supply while energy costs are escalating. One of the ways to conserve energy is to improve thermal insulation of buildings. Aerogels are already showing great promise for wide variety of such applications. This study opens up avenues to design high performance material which is light weight, super-elastic and thermally insulating for applications in buildings, aerospace industry especially in extreme environments. Because of its extreme stretch ability, its appeal is enhanced for various applications.

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{You may read the original research paper by clicking the DOI link given below in the list of cited source(s)}


Source(s)

Zhan, H et al. 2019. Biomimetic Carbon Tube Aerogel Enables Super-Elasticity and Thermal Insulation. Chem. http://dx.doi.org/10.1016/j.chempr.2019.04.025



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Vol.2 Issue 6 June 2019

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