<DIV data thumb = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/tmb/2019/newpolymerfi.jpg" data SRC = "https://3c1703fe8d.site.internapcdn.net/ Newman / GFX / news / 2019 / newpolymerfi.jpg «data sub-HTML =" by mixing the polymer powder in the solution to create a film that they then stretched, MIT researchers modified polyethylene microstructure of spaghetti-like clumps of molecular chains (left) to evenly strands (right), which allows for heat through the polymer, better than most metals loan :. Gang Chen and other. ">
Polymers tend to go to the material for insulation. Think of silicone oven mitt or Styrofoam cups of coffee, and made of a polymeric material that retains heat well.
Now MIT engineers have inverted picture standard polymeric insulator, by manufacturing of thin polymer films that conduct heat capacity normally associated with metals. In experiments, they found films that are thinner than plastic wrap, conducts heat better than many metals, including steel and ceramics.
Team results, published in the journal nature communicationsIt can stimulate the development of composite insulators as light, flexible and corrosion-resistant alternative to traditional metal heat conductors, for applications ranging from heat dissipates materials laptops and mobile phones, the cooling elements of cars and refrigerators.
"We believe that this result is a & # 39 is a step to stimulate the field," said Gang Chen, the Carl Richard Soderberg Professor of Energy at MIT and senior co-author on the paper. "Our vision is more, these properties of polymers can create new applications, and perhaps new industries, and can replace metals as heat exchangers."
coauthors include senior author Chen Yanfei Those, along with Daniel Kremer, BAE songs, Zhou Jiawei, James Loomis, Jianjian Van, Migda Lee Go Ghasemi, Huang Xiaoping and Li Xiaobo from the MIT, and Zhang Jiang from Argonne National Laboratory.
In 2010, the team reported success in the manufacture of thin fibers made of polyethylene, which were 300 times higher thermal conductivity than conventional polyethylene, as well as on how to spend, like most metals. Their results, published in Nature Nanotechnology, attracted the attention of a variety of industries, including heat exchangers manufacturers, computer processors, and even race cars.
It soon became clear that, for polymeric conductors to run on any of these applications, the materials must be extended ultrafine fiber (single fiber is measured by a cell diameter of a human hair) to a more controlled film
"While we were talking, and not a single fiber, we can try to make a letter," said Chen. "It turns out that this is a very laborious process."
The researchers not only had to come up with a way to produce a thermally conductive polymer letters, but they also had to create a special unit to test the thermal conductivity of the material, as well as to develop computer code for image analysis of microscopic structure of the material.
Eventually, the team was able to produce a thin conductive polymer films, since commercial polyethylene powder. Typically, the microscopic structure of the polyethylene polymers and most resembles spaghetti-like entanglement of molecular chains. Heat has a difficult time flowing through this mixed disorder, which explains the internal insulating properties of the polymer, c.
Sowing and colleagues have looked for ways to unravel the molecular polyethylene units, in forming branch circuits at which heat can better hold. To do this, they are dissolved in a solution of polyethylene powder, which caused the roll circuit to expand and untangled. Custom Built flow system further unravel the molecular chain, and spit out the solution on liquid nitrogen plate is cooled to form the film thickness, which was then placed on a roll-to-roll drawing machine which is heated and the film is stretched until it was thinner than the plastic film.
The team then built a machine to test the thermal conductivity of the film. While most polymers conduct heat in the range of 0.1 to 0.5 watts per meter kelvin, this has found a new polyethylene film measured about 60 watts per meter kelvin. (Diamond, better thermal conductivity material comes to approximately 2000 watts per meter kelvin, and ceramic least about 30, and steel, about 15.) As it turns out, the film on command two orders of magnitude greater thermal conductivity than most polymers, as well as more wire than steel and ceramics.
To understand why these engineered plastic films have such an unusually high thermal conductivity, the team conducted experiments on the scattering of X-rays at the US Department of Energy Advanced Photon Source (APS) at the National Laboratory of Argon.
"These experiments, in one of the most brilliant synchrotron X-ray machines in the world, let us see the detail of the nanostructure within the individual fibers comprising the stretched film," says Jiang.
In the preparation of ultrathin films of images, researchers noted that films which have better thermal conductivity consisted of nanofibres from less randomly coiled chains, compared with those in general polymers which resemble spaghetti tangled. Their observations may help scientists engineer the microstructure of the polymer to conduct heat efficiently.
"This work is a dream come true in the end," says Xu.
Looking ahead, the researchers are looking for ways to do more polymeric heat pipes, both by adjusting the manufacturing process and experimenting with different types of polymers.
Zhou shows that the polyethylene film team conducts heat only over the length of the fibers constituting the film. Such unidirectional heat conductor may be useful in conducting heat away in a predetermined direction inside the device, such as portable computers and other electronics. But ideally, he says, that the film must be more effectively dissipate heat in any direction.
"If we have an isotropic polymer with a high conductivity, it is possible to easily mix the material in the composite material, and we have the potential to replace a plurality of conductive materials," says Zhou. "Thus, we are looking for better thermal conductivity in all three dimensions."
color and the thermal properties of the material separately Researchers Tune
Yanfei Xu et al nanostructured polymer films with a metal, the thermal conductivity, nature communications (2019). DOI: 10.1038 / s41467-019-09697-7
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New polymer film conductors of heat, rather than catching it (2019, April 29)
received April 29, 2019
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