China University of Science and Technology develops insulation aerogel imitating polar bear hair
Unlike human or other mammal hair, polar bear hair is hollow. After magnifying under the microscope, each hair has a cavity structure. This hollow tubular structure not only reduces the density of polar bear hair, but also helps to reduce the thermal conductivity, and the amount of heat insulation diffuses from the polar bear's skin surface to the surrounding In low temperature environments, it is worth designing new artificial insulation materials to follow suit.
Inspired by the hollow structure of polar bear hair, the research team led by Professor Yu Shuhong of the University of Science and Technology of China developed a method for artificially synthesizing a hollow carbon tube aerogel (CTA) of polar bear-like hair, which exhibits superelasticity And low thermal conductivity. Relevant research results are titled Biomimetic Carbon Tube Aerogel Enables Super-Elasticity and Thermal Insulation, published in "Chemistry" (Chem 2019, CHEMJOURNAL-D-19-00185R1) on June 6. The first author of the thesis is the doctoral student Zhan Huijuan.
Nature has undergone hundreds of millions of years of development and evolution, and its rich structure and variety are worth learning and developing. The team used one-dimensional nanowires as templates to prepare macro-scale carbon tube aerogels using the template method (Figure 1). Due to its unique microstructure, this aerogel material exhibits excellent light weight, thermal insulation, hydrophobicity and mechanical properties (Figure 2). Its density can be as low as 8 kg / m3, which is lower than most reported thermal insulation materials; its contact angle is 146o, and it can be kept at 56% relative humidity for 120 days, and it can still keep the thermal conductivity basically unchanged; Since the inner diameter of the hollow carbon tube (35 nm) is much smaller than the average free path of the air (75 nm), the air in the tube hardly transfers heat, so the carbon tube aerogel has good thermal insulation performance and its minimum thermal conductivity Only 23 mW m-1 K-1, lower than the thermal conductivity of dry air.
The carbon tube aerogel has a macroscopic three-dimensional network structure, and thus has super elasticity. When the free-falling small steel ball falls on the surface of the carbon tube aerogel, the high rebound speed (1434 mm s-1), even Compressed one million times at 30% strain or 10,000 times at 90% strain, the carbon tube aerogel still keeps the structure intact. The researchers also explored its related properties as a piezoresistive sensor. After compressing 10,000 times at 30% strain, its relative resistance value remained basically unchanged.
This new carbon tube aerogel designed and synthesized by the polar bear hair hollow structure is expected to meet the demand for high-performance materials under extreme conditions, such as lightweight thermal insulation materials and elastomer materials used in the aerospace industry.
The research was supported by the National Natural Science Foundation of China Innovation Research Group, the National Natural Science Foundation of China Key Projects, the Chinese Academy of Sciences Frontier Science Key Research Projects, the Chinese Academy of Sciences Nanoscience Excellence Innovation Center, the Suzhou Nanotechnology Collaborative Innovation Center, etc.
Figure 1. Preparation of CTA. (A) Structure of polar bear hair; (B) Schematic diagram showing the method of preparing CTA using one-dimensional nanowires as templates; (C) Transmission chart of CTA; (D) CTA is compressed under the condition of 90% compression deformation Ten thousand times of stress-strain curve; (E) Thermal infrared image of CTA on a hot stage at 400 ℃, indicating good thermal insulation ability.
Figure 2. Performance characterization of CTA. (A) Comparison of the density of different materials; (B) Comparison of the thermal conductivity of different materials; (C) Comparison of the recovery speed of different materials; (D) CTA compresses one million times under the condition of 30% compression deformation Mechanical properties change; (D) The mechanical properties of CTA are compressed ten thousand times under the condition of 90% compression deformation.
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