IOWA STATE (US) — In the search for organic heat conductors, researchers have discovered spider silks transfer heat better than silicon, aluminum, and pure iron.
Spider silks—particularly the draglines that anchor webs in place—also conduct heat 1,000 times better than woven silkworm silk and 800 times better than other organic tissues.
The journal Advanced Materials recently published a paper detailing the discovery.
“Our discoveries will revolutionize the conventional thought on the low thermal conductivity of biological materials,” according to lead researcher Xinwei Wang, an associate professor of mechanical engineering at Iowa State University.
Spider hunch
Wang had a hunch that spider webs were worth a much closer look.
So he ordered eight spiders—Nephila clavipes, golden silk orbweavers—and put them to work eating crickets and spinning webs in the cages he set up in an Iowa State greenhouse.
Wang studies thermal conductivity, the ability of materials to conduct heat. He’s been looking for organic materials that can effectively transfer heat. It’s something diamonds, copper and aluminum are very good at; most materials from living things aren’t very good at all.
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But spider silk has some interesting properties: it’s very strong, very stretchy, only 4 microns thick (human hair is about 60 microns) and, according to some speculation, could be a good conductor of heat. But nobody had actually tested spider silk for its thermal conductivity.
And so Wang, with partial support from the Army Research Office and the National Science Foundation, decided to try some lab experiments. Xiaopeng Huang, a post-doctoral research associate in mechanical engineering; and Guoqing Liu, a doctoral student in mechanical engineering, helped with the project.
“I think we tried the right material,” Wang says of the results.
The paper reports that using laboratory techniques developed by Wang—”this takes time and patience”—spider silk conducts heat at the rate of 416 watts per meter Kelvin. Copper measures 401. And skin tissues measure .6.
“This is very surprising because spider silk is organic material,” Wang says. “For organic material, this is the highest ever. There are only a few materials higher—silver and diamond.”
Even more surprising, he says, is when spider silk is stretched, thermal conductivity also goes up. Wang says stretching spider silk to its 20 percent limit also increases conductivity by 20 percent. Most materials lose thermal conductivity when they’re stretched.
That discovery “opens a door for soft materials to be another option for thermal conductivity tuning,” Wang writes in the paper.
That could lead to spider silk helping to create flexible, heat-dissipating parts for electronics, better clothes for hot weather, bandages that don’t trap heat, and many other everyday applications.
Why spider silk?
Wang says it’s all about the defect-free molecular structure of spider silk, including proteins that contain nanocrystals and the spring-shaped structures connecting the proteins. More research needs to be done to fully understand spider silk’s heat-conducting abilities, Wang adds.
Wang is curious if spider silk can be modified in ways that enhance its thermal conductivity. He says the researchers’ preliminary results are very promising.
More news from Iowa State University: www.news.iastate.edu/
