Dec
9
A Plastic Designed to Conduct Heat
December 9, 2014 | Leave a Comment
A University of Michigan (UM) team led by Professor Jinsang Kim and Associate Professor Kevin Pipe developed a new polymer plastic that disperses heat better than other polymers. The UM research team has made a plastic blend that does so 10 times better than its conventional counterparts.
Plastic Blend of Polyacrylic Acid with Short Strands of Polyacryloyl Piperidine. The new blend relies on hydrogen bonds that are 10-to-100 times stronger. Image Credit: University of Michigan. Click image for the largest view.
While plastics are inexpensive, lightweight and flexible they restrict the flow of heat. That causes their use to be limited in technologies like computers, smartphones, cars or airplanes, the types of places that could benefit from their properties but where heat dissipation is also important.
Its the spaghetti-like internal structure of most plastics makes it hard for them to move and cast off heat. The new UM work could lead to light, versatile, metal-replacement materials that make possible more powerful electronics or more efficient vehicles and many other applications.
The new material is actually a blend, a result from one of the first attempts to engineer the flow of heat in an amorphous polymer. A polymer is a large molecule made of smaller repeating molecules. Plastics are common synthetic polymers.
Previous efforts to boost heat transfer in polymers have relied on metal or ceramic filler materials or stretching molecule chains into straight lines. Those approaches can be difficult to scale up and can increase a material’s weight and cost, make it more opaque, and affect how it conducts electricity and reflects light. The UM material has none of those drawbacks, and the researchers said it’s easy to manufacture with conventional methods.
Kevin Pipe, UM associate professor of mechanical engineering and corresponding author of the paper titled “High Thermal Conductivity in Amorphous Polymer Blends by Engineered Interchain Interactions”on the work published in the current issue of Nature Materials said, “Researchers have paid a lot of attention to designing polymers that conduct electricity well for organic LEDs and solar cells, but engineering of thermal properties by molecular design has been largely neglected, even though there are many current and future polymer applications for which heat transfer is important.”
Heat energy travels through substances as molecular vibrations. For heat to efficiently move through a material it needs continuous pathways of strongly bound atoms and molecules. Otherwise, the thermal stalls like a trap and the substance stays hot.
Pipe explained, “The polymer chains in most plastics are like spaghetti. They’re long and don’t bind well to each other. When heat is applied to one end of the material, it causes the molecules there to vibrate, but these vibrations, which carry the heat, can’t move between the chains well because the chains are so loosely bound together.”
The Pipe and Kim research groups devised a way to strongly link long polymer chains of a plastic called polyacrylic acid (PAA) with short strands of another called polyacryloyl piperidine (PAP). The new blend relies on hydrogen bonds that are 10-to-100 times stronger than the forces that loosely hold together the long strands in most other plastics.
Kim pointed out, “We improved those connections so the heat energy can find continuous pathways through the material. There’s still a long way to go, but this is a very important step we made to understand how to engineer plastics in this way. Ten times better is still a lot lower heat conductivity than metals, but we’ve opened the door to continue improving.”
To arrive at these results, the researchers blended PAP plastic strands separately with three other polymers that they knew would form hydrogen bonds in different ways. Then they tested how each conducted heat.
Gun-Ho Kim, first author of the paper and a postdoctoral fellow in mechanical engineering and materials science and engineering fills out the results with, “We found that some samples conducted heat exceptionally well. By performing numerous measurements of the polymer blend structures and their physical properties, we learned many important material design principles that govern heat transfer in amorphous polymers.”
The two other first authors are Dongwook Lee and Apoorv Shanker, graduate students in macromolecular science and engineering.
Professor Kim noted, ” . . . we’ve opened the door to continue improving.” You can bet there will be a big group of folks following up on this one. Keep in mind that the conduction doesn’t need to be in the silver copper and aluminum range. It just has to be a lot better than the typical engineering choices of today.
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