Material scientists design polar bear hair-inspired heat insulator

Materials World magazine
,
7 Jun 2019

By reproducing the structure of individual polar bear hairs, a lightweight, stretchy heat insulation material has been created.

Studying the insulating properties of polar bears – provided by their fat, skin, and fur, materials scientists from the University of Science and Technology of China (USTC) have developed a synthetic insulator that mimics the properties of polar bear hair. The team are scaling toward a material composed of many hairs for real-world applications in the architecture and aerospace sectors. 

Recently published in the journal Chem, the study shown that the insulator has a similar hollow structure to that of polar bear hair. On a microscopic inspection, polar bear hair is a long cavity, shaped as a cylinder, through its centre that gives the bear significant heat-holding capabilities. 

‘Polar bear hair has been evolutionarily optimized to help prevent heat loss in cold and humid conditions, which makes it an excellent model for a synthetic heat insulator,’ said USTC Chemistry Professor and co-senior author, Yu Shuhong. 

‘By making tube aerogel out of carbon tubes, we can design an analogous elastic and lightweight material that traps heat without degrading noticeably over its lifetime.’

It is widely recognised that polar bear’s distinctive white coats is a result of the shapes spacing of the cavities. The hair not only has remarkable heat-holding properties, but it is also water resistant and stretchy – desirable properties to imitate in a thermal insulator. 

‘The hollow centres limit the movement of heat and also make the individual hairs lightweight, which is one of the most outstanding advantages in materials science,’ said USTC Associate Professor Jian-Wei Liu. The researchers imitated the structure and scale to a practical size by manufacturing millions of hollowed-out carbon tubes, each equivalent to a single strand of hair, and wound them into a spaghetti-like aerogel block. 

According to the study, as the air inside the tiny cavity is only 35 nanometres in its inner diameter, the heat conductivity of the material is even lower than that of dry air. The minimum density of the material is also only eight kilograms per cubic meter, making it lighter than the majority of other aerogels and insulation components. The new material was extraordinarily elastic, and it could maintain its structure after one million compress-release cycles at a 30% strain, which further boosts its engineering applicability. 

The next step for the team is to scale up the manufacturing process to make itrelevant for industrial uses. ‘While our carbon-tube material cannot easily be mass produced at the moment, we expect to overcome these size limitations as we work toward extreme aerospace applications,’ said Yu. An approach to scalability can be achieved by building insulators on the meter scale rather than the centimetre one.