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John O | June 2019

Scientists use polar bear hair as template for building new thermal insulating material


By Josh Perry, Editor
jperry@coolingzone.com

 

Researchers from the University of Science and Technology of China (USTC) in Hefei reproduced the structure of individual polar bear hairs with tube aerogels composed of carbon nanotubes to build a new material that could be as effective an insulator as the natural version.

 


This image shows electron microscopy of the hollow bioinspired carbon tube aerogel.
(Hui-Juan Zhan)

 

According to a press release from the school, polar bear hair prevents heat loss in cold and humid conditions and have long been a guide to building synthetic insulators for applications such as architecture and aerospace.

 

“Unlike the hairs of humans or other mammals, polar bear hairs are hollow,” the release continued. “Zoomed in under a microscope, each one has a long, cylindrical core punched straight through its center. The shapes and spacing of these cavities have long been known to be responsible for their distinctive white coats. But they also are the source of remarkable heat-holding capacity, water resistance, and stretchiness, all desirable properties to imitate in a thermal insulator.”

 

The hollow structure also makes the hairs lightweight, another property long coveted by materials scientists. The USTC researchers created millions of hollowed-out carbon nanotubes and wound them together in a “spaghetti-like aerogel block.” They discovered that this material was lighter and more resistant to heat flow than previous aerogels.

 

“As a bonus, the new material was extraordinarily stretchy, even more so than the hairs themselves, further boosting its engineering applicability,” the release added. Scaling this breakthrough for commercial applications will be the next step for researchers.

 

The research was recently published in Chem. The abstract stated:

 

“Inspired by microstructures of polar bear hair, herein, we describe a simple solution-based strategy to fabricate a macroscopic-scale and lightweight carbon tube aerogel with super-elasticity and excellent thermal insulation. The microstructure-derived thermal conductivity and super-elasticity are strongly dependent on the shell thickness of the interconnected tubes, as well as the aperture of the aerogel.

 

“Remarkably, the optimized aerogel can maintain structural integrity after more than one million compress-release cycles at 30% strain and 10,000 cycles at 90% strain. Moreover, this biomimetic aerogel offers a fast and accurate dynamic piezoresistive response to broad bandwidth frequency forces.

 

“Particularly, the super-elasticity is further confirmed by its fastest rebounding speed of 1,434 mm s−1 among the traditional elastic materials measured by a standard falling steel ball. Furthermore, the optimized minimum thermal conductivity is as low as 23 mW m−1 K−1 which performs better than the thermal conductivity of dry air.”

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