MIT Scientists Make a Polyethylene Heatsink

arcticstoat calls our attention to MIT research that has produced a version of polyethylene that can conduct heat away from computer chips. Polyethylene is the most widely used plastic. It's not clear how practical this research is for industrial-scale use, involving as it does an atomic-force microscope. The work is detailed in a paper published in Nature Nanotechnology this month. "The new process causes the polymer to conduct heat very efficiently in just one direction, unlike metals, which conduct equally well in all directions. ... 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 fiber 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 fiber. This fiber was about 300 times more thermally conductive than normal polyethylene along the direction of the individual fibers, says the team’s leader..."

Comments

Re:Article is wrong.

[krnpimpsta]

Yes, I was really intrigued and confused, after reading the line:

"The new process causes the polymer to conduct heat very efficiently in just one direction,"

I was thinking, wow, is this even possible? If this is true, I think they've just created a material that could behave like a passive air-conditioner, heater, refridgerator, etc., while using NO power, ever. That alone must be breaking some serious laws of thermodynamics..

"One dimension" or "one axis," would have been more appropriate than "one direction."

Thermal conductivity

[MartinSchou]

Since neither the summary nor the article has been kind enough to expand on "300 times more thermally conductive than normal polyethylene", I figured I'd look it up.
Thermal Conductivity of some common Materials:
Polyethylene HD: 0.42 - 0.51 W/mK
Aluminium: 250W/mK
Copper: 401 W/mK

Best case scenario: 153 W/mK or 61% as conductive as aluminium, 38% as conductive as copper. Not exactly impressive for a heat sink

Re:Thermal conductivity

[jank1887]

don't forget the rest, though:

Density:
copper: 8.96g/cm3
aluminum: 2.7 g/cm3
silicon: 2.33 g/cm3
AluminumNitride (high thermal conductivity insulating ceramic, k~160to190W/mK): 3.33g/cm3

LDPE and HDPE: 0.92-0.97 g/cm3.

So, you're getting a factor of 2-10x in weight savings. Tell that to a aerospace designer and he'll make it work. It's also a cheap material (well, feedstock's cheap. and normal PE is cheap, especially relative to copper these days). Who knows how expensive this stuff might be if they can make more than single fibers.

Re:Article is wrong.

[srussia]

krnpimsta said:

Yes, I was really intrigued and confused, after reading the line: "The new process causes the polymer to conduct heat very efficiently in just one direction,"

You said:

You connect a heat source to the bottom of a water tank, as it heats water on the bottom, the density of water in vicinity decreases and flow upward in one direction.

He was talking about conduction. You're talking about convection.

Re:What about therm interface Re:Thermal conductiv

[metamechanical]

The problem with that is that most likely, the interface for the Polyethylene heat sink would be worse than for an aluminum one; The Polyethylene molecule is vastly more complicated than the Aluminum atom, and not nearly as mobile once cast (and would be just as likely to capture little insulating pockets of air, etc.). Even if the Polyethylene molecules on the end could "mold" to the interface, there is not guarantee they wouldn't flop over and become insulating - an Aluminum sink "molded" to the interface wouldn't care, as it's isothermal.

Re:Heat Diode

[clone53421]

No, they did not.

They built a material that allows heat to flow along one axis. It can go either way through it, but only in that one dimension.