신기하네~ 열 전달하는 플라스틱 Heat-conducting plastic developed at U-Michigan
김진상 美 미시간대 교수팀,
기존보다 10배나 열 잘 전달하는 플라스틱
source ns.umich.edu
연구진은 길고 짧은 고분자 사슬(파랑, 녹색)을 강력하게 결합(빨강)시키는
방식으로 플라스틱 내부에 열이 전달되는 통로(노랑)를 만들었다.
- 네이처 머티리얼스 제공
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가볍고 유연한 플라스틱이 열을 잘 전달하지 않는다는 사실은 상식이다. 하지만 재미 과학자가 이끈 미국 연구진이 기존 플라스틱의 장점에 열을 잘 전달하는 성질까지 더해 활용도를 높이는 데 성공했다.
김진상 미국 미시간대 교수팀은 케빈 파이프 교수팀과 공동으로 기존 플라스틱보다 열을 10배나 더 잘 전달하는 플라스틱을 개발했다고 7일 밝혔다.
지금까지 열을 잘 전달하는 고분자 물질을 만들려면 금속이나 세라믹 재료를 추가로 넣는 방식을 써 왔다. 이 방식으로는 무게와 가격이 올라가고 투명하게 만들기 어렵다는 한계가 있었다.
연구진은 열에너지가 분자진동을 통해 전달된다는 점에 초점을 맞췄다. ‘폴리아크릴산(PAA)’이라는 긴 고분자 사슬과 ‘폴리아크릴로일 피레리딘(PAP)’이라는 짧은 고분자 물질을 사용해 서로 강력하게 결합시키는 방법을 개발해 열이 연속적으로 전달되는 ‘통로’를 만들 수 있었다. 기존 플라스틱은 각 고분자 사슬들이 길고 느슨하게 결합돼 있어서 열이 잘 전달되지 않았다.
이렇게 만든 플라스틱은 기존 플라스틱보다 수소결합력이 10~100배나 강력했으며 실제로 열을 10배나 잘 전달하는 것으로 나타났다.
김 교수는 “아직 금속이 열을 전달하는 능력의 10분의 1에 불과하지만 성능을 끌어올릴 수 있는 해법을 찾은 만큼 추가 실험을 진행하고 있다”고 말했다.
이 연구결과는 ‘네이처’의 자매지 ‘네이처 머티리얼스’ 지난달 24일자에 실렸다.
동아사이언스 이재웅 기자 ilju2@donga.com |
Heat-conducting plastic developed
at U-Michigan
|
Nicole Casal Moore ANN ARBOR—The spaghetti-like internal structure of most plastics makes it hard for them to cast away heat, but a University of Michigan research team has made a plastic blend that does so 10 times better than its conventional counterparts. Plastics are inexpensive, lightweight and flexible, but because they restrict the flow of heat, their use is limited in technologies like computers, smartphones, cars or airplanes—places that could benefit from their properties but where heat dissipation is important. The new U-M work could lead to light, versatile, metal-replacement materials that make possible more powerful electronics or more efficient vehicles, among other applications. The new material, which is actually a blend, results 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 U-M material has none of those drawbacks, and it's easy to manufacture with conventional methods, the researchers say. "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," said Kevin Pipe, U-M associate professor of mechanical engineering and corresponding author of a paper on the work published in the current issue of Nature Materials. Pipe led the project with Jinsang Kim, another corresponding author and associate professor of materials science and engineering. 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, it gets trapped, meaning the substance stays hot. "The polymer chains in most plastics are like spaghetti," Pipe said. "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. "We improved those connections so the heat energy can find continuous pathways through the material," Kim said. "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. "We found that some samples conducted heat exceptionally well," said Gun-Ho Kim, first author of the paper and a postdoctoral fellow in mechanical engineering and materials science and engineering. "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." Two other first authors are Dongwook Lee and Apoorv Shanker, graduate students in macromolecular science and engineering. The paper is titled "High thermal conductivity in amorphous polymer blends by engineered interchain interactions." The research was funded by the U.S. Department of Energy, Office of Basic Energy Sciences as part of the Center for Solar and Thermal Energy Conversion in Complex Materials, an Energy Frontier Research Center. Gun-Ho Kim has also received a fellowship from the U-M Energy Institute. Related Links:
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