Polar bear cold protection "black technology": use fur to keep still air
In early 2021, the extremely cold weather is still raging in some parts of the northern hemisphere, and Spain has suffered a super snowfall that has not been encountered in a century.
Before the arrival of spring, we still have to endure the cold and work hard to keep ourselves warm.
When it comes to warm clothing, in addition to fur coats protested by environmentalists, down jackets are currently the best choice.
But did you know: The technology used in down jackets is inspired by the most cold-proof creature on the planet-the polar bear?
In extreme cold weather, wind and water are the real enemies.
Imagine the feeling of falling into an ice cave, and the Titanic passengers who died in the cold water.
However, even in the coldest weather, polar bears can play on icebergs and swim more than 10 kilometers in the waters of the Arctic Ocean.
The fur of the polar bear can be said to be the most warm "natural clothing" in the world at this stage. The "black technology" contained in it can be said to be very powerful.
Black skin absorbs heat
Hollow capillary to keep warm
The fur of the polar bear is the best "natural clothing" on earth to keep warm.
People's winter clothing filled with thermal cotton, down jackets and heat reflection technology of cotton jackets all use bionic technology related to polar bear fur.
Here is a simple and key knowledge point: still air is a material with very low thermal conductivity, in other words it is a very warm material (when the air is still, heat convection cannot be generated, thereby reducing heat loss).
The main reason why the fur of the polar bear can keep warm is to "catch" and stabilize the air.
In fact, the reason why down can keep warm is also because the fibers can fix air; synthetic thermal cotton can keep warm, because the fibers are made into hollow tubes, and still air can be kept between the fiber pipes and the fibers.
There are two layers of fur on the polar bear. The outer layer is waterproof needle hair that contains grease, which can prevent seawater from intruding when swimming, and the inner layer is warm fluff.
Put the "white hair" of the polar bear under an electron microscope, you will find that the polar bear's hair is not white, but hollow and transparent hair tubes (see the lower right picture).
The "white" seen by human eyes is formed because the inner surface of the hair is rough and uneven, so that the light is refracted very messy.
The hair of each polar bear is about 15 cm long and the diameter is about the same thickness as a human hair.
If you look closely under a microscope, you will find that in addition to the middle tube, there are many more narrow and long translucent small holes around, which also stretch in the same direction.
In the hollow hair tube of a polar bear, there is a lot of still air. As mentioned above, still air has low thermal conductivity, so polar bear hair is an excellent thermal fiber.
Similarly, the reason why down keeps warm is that a lot of still air is locked between the down yarns to keep it warm, which is similar to polar bear hair.
In addition to the fur, the polar bear’s skin also has a warmth-its skin is black. This can be seen from the polar bear’s nose, paw pads, lips and the black skin around the eyes.
As we all know, black absorbs heat, so black skin also helps absorb heat.
The researchers also found that the special transparent capillary tube of the polar bear allows high-energy ultraviolet rays in the air to pass along the inside of the hair core, reflect to the black skin under the hair, and convert it into heat, which is then transported to the body by the blood under the skin.
Not only that, the fur of polar bears can also reflect infrared radiation.
Polar bears, like humans, are warm-blooded animals, radiating heat at all times, that is, thermal radiation.
But its "black technology" fur wraps its body, but it can fully reflect the body's heat radiation, so as to achieve the effect of almost no heat leakage.
How powerful is this effect?
Let's put it this way, even when shooting with an infrared camera, it is almost impossible to detect heat.
Imitating hair with silk
Imitate skin with aluminum foil
The fur of the polar bear is waterproof and warm. It can absorb ultraviolet heat and block the body heat. This series of magical structures makes it the warmest "clothing" in the world. It also gives mankind a lot of inspiration and develops related bionic product.
For example, with the structure of polar bear hair, the outer layer is waterproof, and the inner layer is hollow tubular warm cotton.
In 2018, the scientific research team of the School of Chemical Engineering and Biological Engineering of Zhejiang University also used a unique "freeze spinning" to spin almost a kind of man-made fiber, whose thermal insulation performance is comparable to that of polar bear hair.
The scientific research team used a 5% natural silk protein aqueous solution, after cooling it through a special process, the solution was re-shaped into fibers.
After these fibers are freeze-dried, they leave a strip of "imitation wool" composed of silk protein.
The thermal conductivity of this material is lower than that of natural polar bear hair, and it has better heat retention.
It's just a pity that this technology is currently limited to laboratories, and there is no way to achieve large-scale, low-cost mass production.
If mass production can be achieved in the future, then lighter and warmer winter clothes will surely become popular.
At that time, we may say goodbye to the heavy coat, put on a thin "artificial sweater" and go out;
In addition, in the structure of the early spacesuits, there were several layers of aluminum foil interlayers, which also imitated the fur of a polar bear, and kept warm by reflecting the heat radiation of the body.
In October 2019, NASA released a new generation of more flexible and safer spacesuits.
This kind of extravehicular spacesuit can work at temperatures between minus 157 degrees Celsius and above zero 121 degrees Celsius, protecting astronauts from radiation, moon dust and micrometeoroids.
This type of bionic technology is still under continuous development and is expected to exceed the warmth retention effect of polar bear fur.
(Brown squirrel)