Mar
12

A polymer material that could dissipate heat

Most polymers — materials made of long, chain-like molecules — are very good insulators for both heat and electricity. But an MIT team has found a way to transform the most widely used polymer, polyethylene, into a material that conducts heat just as well as most metals, yet remains an electrical insulator.

thermoconductive polymer

The illustration to the left displays the tangled nature of the polymer filaments, with heat-stopping voids indicated as dark blobs. When drawn and heated into a thin thread (illustration to the right), the molecules line up and the voids are compressed, making the material a good conductor (illustrations courtesy of Gang Chen).

The new process causes the polymer to conduct heat very efficiently in just one direction, unlike metals, which conduct equally well in all directions. This may make the new material especially useful for applications where it is important to draw heat away from an object, such as a computer processor chip. The work is described in a paper published in Nature Nanotechnology.

The key to the transformation was getting all the polymer molecules to line up the same way, rather than forming a chaotic tangled mass, as they normally do. The team did that by slowly drawing a polyethylene fibre out of a solution, using the finely controllable cantilever of an atomic force microscope, which they also used to measure the properties of the resulting fibre.

This fibre was about 300 times more thermally conductive than normal polyethylene along the direction of the individual fibres, says the team’s leader, Gang Chen, professor of power engineering and director of MIT’s Pappalardo Micro and Nano Engineering Laboratories.

The high thermal conductivity could make such fibres useful for dissipating heat in many applications where metals are now used, such as solar hot water collectors, heat exchangers and electronics. Chen explains that most attempts to create polymers with improved thermal conductivity have focused on adding in other materials, such as carbon nanotubes, but these have achieved only modest increases in conductivity because the interfaces between the two kinds of material tend to add thermal resistance. “The interfaces actually scatter heat, so you don’t get much improvement,” Chen says. But using this new method, the conductivity was enhanced so much that it was actually better than that of about half of all pure metals, including iron and platinum.

Producing the new fibres, in which the polymer molecules are all aligned instead of jumbled, required a two-stage process, explains graduate student Sheng Shen, the lead author of the paper. The polymer is initially heated and drawn out, then heated again to stretch it further. “Once it solidifies at room temperature, you can’t do any large deformation,” Shen says, “so we heat it up twice.”

Even greater gains are likely to be possible as the technique is improved, says Chen, noting that the results achieved so far already represent the highest thermal conductivity ever seen in any polymer material. Already, the degree of conductivity they produce, if such fibres could be made in quantity, could provide a cheaper alternative to metals used for heat transfer in many applications, especially ones where the directional characteristics would come in handy, such as heat-exchanger fins (like the coils on the back of a refrigerator or in an air conditioner), cell-phone casings or the plastic packaging for computer chips. Other applications might be devised that take advantage of the material’s unusual combination of thermal conductivity with light weight, chemical stability and electrical insulation.

So far, the team has just produced individual fibres in a laboratory setting, Chen says, but “we’re hoping that down the road, we can scale up to a macro scale,” producing whole sheets of material with the same properties. Ravi Prasher, an engineer at Intel, says that “this is a very significant finding” that could have many applications in electronics. The remaining question, he says, is “how scalable is the manufacturing of these fibres? How easy is it to integrate these fibres in real-world applications?”

Source: original article

6 Comments to “A polymer material that could dissipate heat”

  • Soohie Friday April 9th, 2010 at 03:28 PM

    bonjour, ton blog est super genial, continue sur cette voie.

  • Chase D. Saturday April 10th, 2010 at 01:59 AM

    Wow this is a great resource.. I’m enjoying it.. good article

  • Lillian S. Thursday July 8th, 2010 at 08:34 AM

    Very interesting.

  • Prof. Dr. Lubos Hes, FTI (hon). Friday July 9th, 2010 at 09:48 AM

    Dear Sirs,
    I am excited. I would like to cooperate with Prof. Gang Chen direclly. I am inventor of various commercialized instruments for the measurment of low thermal conductivity of textiles and common polymers (till 1 W/m. K), but recently we have invented and we will also patent a new instrument for the steady – state measurement of thermal conductivity of carbon composites, with lambda over 50 W/m. K. We are now receiving orders for this instrument.
    2 prototytypes succesfully working at the Tech,. Univ. of Liberec, Czech Republic and Aachen Univ. in Germany.
    I am sure I can also contribute to the development of PE components with high lambda – we have got enough experience of the heat scattering in the interfaces.
    Please answer to my e-mail address.

  • Jorge Tobar Friday July 9th, 2010 at 12:48 PM

    Excelente investigación.

  • Telefon Schnurloses Sunday August 15th, 2010 at 09:39 AM

    the valuable thoughts you presented do help our team’s investigation for my company, appreciate that.

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