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Warm "black technology" into reality!"Frozen spinning" technology shows great power! Feb 01, 2021

Warm "black technology" into reality!"Frozen spinning" technology shows great power!
A new round of cold air is moving south to "quick-freeze" Zhejiang Province after the aftereffects of the "overweening" cold wave have not dispersed.
According to the latest meteorological data analysis, affected by two cold air, Zhejiang will have continuous temperature drop, severe freezing, strong wind and light rain (snow) weather in the next few days.

Cold wave coincides with the "39" days, the north wind whistling on the face, how a "cold" word!
Have you done enough to keep warm on the way to work and school?
Want to have a set of "dark tech" clothes that are as warm as under the sheets?

Now, "dark tech" has come true.
The reporter interviewed Bai Hao, professor of College of Chemical Engineering and Biological Engineering of Zhejiang University, Lin Shisheng, professor of College of Information and Electronic Engineering, and Gao Chao, professor of Department of Polymer, to bring us into the forefront of thermal science.


▲ Bionic fiber prepared by the team of Baihao


Winters in the Arctic are long and cold, with surface temperatures as low as -50 ° C in most areas.

The polar bears, who live here without heat or bed, have to rely on thick "mink coats" to fight the polar cold.


Polar bears share a common ancestry with brown bears, scientific research has found.

With that white coat off, a polar bear's skin is actually black.

What's the secret to the polar bear's dense white fur, which completely covers the bear's body heat and effectively insulates it from the icy outdoors?


Bai Hao, a professor at the School of Chemical Engineering and Biological Engineering of Zhejiang University, said that the feel of polar bear hair is similar to the thick human hair.

Under an electron microscope, the cross section of a polar bear's hair looks like a tube filled with holes.

This structure has a very good reflection effect on the infrared rays inside the light.

At the same time, in cold weather, it can trap a lot of air, efficiently storing heat and transporting it to the polar bear's body surface.


▲ Put on "polar bear fur"
Inspired by polar bear hair, the Bochao team developed a technique called "freeze spinning."
The silk was dissolved in water to make a spinning solution with 95% water content.
Then a syringe is used to slowly squeeze the spinning solution into the freezing device to form a monofilament with a diameter of about 200 microns.
Finally, by freeze-drying, the ice crystals in the fibers are sublimated, leaving numerous ordered lamellar pores.
Thermal conductivity is the physical quantity of the heat conduction ability of the material, the lower the thermal conductivity, the more warm.
It is known that the thermal conductivity of still air is 26, and that of natural polar bear hair is about 27, which is very close to the thermal conductivity of still air.
The bionic fiber prepared by the team of Baihao has the lowest thermal conductivity of 19.
"This ordered porous fibrous material, like a polar bear's fur, has a number of evenly sized voids that insulate the cold air from the outside, providing a highly efficient insulation capability."
BaiHao said.

Bau Ho also told reporters that the bionic fiber is 95 percent air, silk is only 5 percent.
Compared with down jackets, the material cost of bionic fibers is relatively low.

In addition to the insulation, the bionic fiber can add more functions that are badly needed in winter.
The Bochao team created the electrically heated fabric by adding carbon nanotubes to the bionic fibers.
"At 5 volts, the temperature of the electrically heated fabric can rise from 24℃ to 36℃ in a minute.
That means it can be passively insulated or actively generated."
The team has also recently developed heat-resistant insulation fabrics and underwater insulation fabrics to explore more possibilities for bionic fibers, says Bow Ho.


Bring the graphene

From obscure niche brands to well-known head brands, the word "graphene" frequently appears in the propaganda of various thermal insulation products, becoming a synonym for "black technology".

What is graphene?

Why can it become "hot property"?

Like diamond, graphite is a substance made of the element carbon.

Diamond is the hardest natural gemstone on the surface, while graphite, on the contrary, is in the same Mos hardness range as talc, the softest known mineral.

Graphene is a thin sheet of carbon atoms that form a hexagonal ring between them. The rings connect to form a honeycombed plane, and one layer on top of another makes graphite.

Swipe a pencil across the paper, and what you're left with are several or even dozens of layers of graphene.


As a single atomic layer of material, one of the characteristics of graphene is thin, it is the world's thinnest material.

It's only about one atom thick, about 0.3 nanometers, and about 60,000 layers of graphene are about the thickness of a human hair.

Thin, strong, conductive, heat conduction......

These properties of graphene give people a lot of imagination.


"Graphene opens the door to the study of atom-thick materials, allowing us to explore new materials at a quantized level."

Zhejiang University College of Information and Electronic Engineering Professor Lin Shisheng said.


To make graphene, you have to make the graphite thin.

We certainly had the experience when we were kids, when we made a mistake on a piece of paper, we used Scotch tape to get it out.


In 2004, Geim and Novoselov of the University of Manchester in the United Kingdom repeatedly pasted and ripped a piece of graphite with transparent adhesive, gradually reducing the thickness of the graphite sheet, and finally forming graphene with a thickness of only 0.335 nanometers.

This is the first time in the world that a single layer of graphene has been made.


Lin's team has focused on graphene research for many years.

A Bluetooth smart temperature-controlled graphene scarf has left the lab.

According to the introduction, the thick graphene film in the lining of the scarf can be heated to 30℃ to 60℃, and the built-in mobile power supply placement area can be recycled charging, and the temperature of the scarf can be precisely controlled at the appropriate temperature through the mobile APP.


"In fact, graphene doesn't heat up on its own.

"It's only when an electric current is passed through that electrons run very quickly through the graphene, colliding with the carbon atoms, causing them to vibrate and radiate infra-red light, which warms the body."

So we had to connect to an external power source to "charge" the graphene suits while wearing them, Lin said.


Lin Shi-sheng told reporters that the electron movement speed in the graphene is close to 300 times the speed of light, the radiation area is large, the heat conduction ability is strong, so the graphene heating efficiency is very high.

At the same time, the heat distribution of graphene is very uniform, there is no local hot spots.

Graphene also has a strong battery life, which allows it to generate the most heat with the least amount of electricity.


Using Bluetooth smart temperature control, for example, a graphene scarf can be kept at 42 ° C for 11 to 12 hours.

Moreover, graphene emits far-infrared light waves with wavelengths ranging from 8 microns to 14 microns after being electrified, which corresponds to the infrared wavelengths of the human body, like a miniature portable "therapy apparatus" that can promote blood circulation.


Graphene scarves, graphene blankets, graphene thermal clothing...

In the future, there will be more graphene products into People's Daily life, when you put on different graphene products, you can freely control the temperature of the corresponding parts.

"We hope to achieve an intelligent temperature control system by linking graphene to the smart chip, so that the temperature control system is convenient, intelligent, chip-based and humanized."

Lin Shisheng said that graphene intelligent temperature control system, including heat dissipation and heating, is not only for clothing, but also can be applied to a wide range of fields such as new energy vehicles, mobile phones and 5G base stations in the future.


Discriminate between warm science and fiction


The current market is labeled "high-tech" warm clothes, so dazzling, difficult to distinguish.

There is both real science and pseudoscience.


Department of high polymer of Zhejiang University professor superb thinks, many products on the current market only hit concept, without immanence.

For example, some so-called graphene thermal clothing is actually made of metal wire inside, and lacks good temperature control ability, which may cause the risk of scalding the body because the temperature is too high at one point.


"We had our spinning grade single-layer GO 10-ton production line back in 2019, which was internationally certified.

It is because of our production experience that we can see what products have problems when we test them."

The healthy multifunctional graphene composite fibers developed by the Gaogao team are now used in clothing such as sweaters.


The sweater can "lock in" body heat, causing the wearer's body temperature to rise three to four degrees quickly.

"Even on a cold winter day, a sweater and a coat are enough. There is no need for a heavy down jacket."

Superb said.


Gao pointed out that studies have shown that the surface of oxidized graphene contains a large number of oxygen-containing functional groups, which can produce reactive oxygen species (ROS) to cause oxidative stress and disrupt the bacterial metabolism process, thus inhibiting or killing bacteria.

In addition, the team produced graphene products with UV protection, anti-static, negative ion generation and other functions.


While breaking the superstition of "pseudoscience", true science shines in the field of scientific research.


Aerogel, as a new solid material of nano-porous structural materials, has excellent properties such as ultra-light, heat insulation, transparency, heat preservation and fire prevention. It has been awarded the title of "the lightest solid in the world" by Guinness World Records.


Since aerogel is typically more than 80 percent air, it has a very good insulating effect. An inch thick aerogel can insulate as well as 20 to 30 ordinary pieces of glass.

Aerogel also has a variety of applications in space exploration, including the Russian space station Mir and the American Mars Pathfinder probes.


At present, some researchers in China have developed an aerogel using Kevlar fiber.

Compared with ordinary thermal insulation materials, it can perform thermal insulation performance at extremely low and extremely high temperatures for a long time.


Data show that the new material can protect against cold and heat in temperatures ranging from minus 196 degrees Celsius to 300 degrees Celsius.

At minus 60 degrees Celsius, it holds heat 2.8 times better than cotton fiber.

Compared with hollow fiber and microfiber, two of the best man-made insulation fiber materials on the market, the new material also has significantly better insulation performance.


In addition, the aerogel fiber has excellent chemical stability and can be modified by dyeing, hydrophobic and electroless plating without damaging the skeleton structure of aerogel.


"The characteristics of aerogel with light weight and good thermal insulation also meet our requirements for winter warm clothing, but it is only used in industry for a variety of reasons at present, and its safety and effectiveness are still to be verified."

Superb said.



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