Spider Silk Found To Have High Heat Conductivity

Xinwei Wang, an associate professor of mechanical engineering at Iowa State University, and his research team recently discovered that spider silk---particularly the draglines that anchor webs in place---conducts heat better than most materials. Spider silk even conducts heat better than silicon, aluminum, and pure iron. Furthermore, it conducts heat 1000 times better than woven silkworm silk and 800 times better than other organic tissues. Wang based his discovery on webs spun by golden silk orbweavers in an Iowa State greenhouse. He had some support from the Army Research Office and the National Science Foundation.

(Silk studied for its potential medical applications has appeared a few other times on this blog recently. See this story and this one. News about spider silk, specifically, includes this story from 2010.)

An article about Wang's discovery, "New Secrets of Spider Silk: Exceptionally High Thermal Conductivity and its Abnormal Change under Stretching," was published online by the journal Advanced Materials. "Our discoveries will revolutionize the conventional thought on the low thermal conductivity of biological materials," Wang wrote in the article.

By way of laboratory techniques developed by Wang, spider silk conducts heat at the rate of 416 watts per meter Kelvin, according to the Advanced Materials article. To put this in context, copper measures 401. Skin tissues measure 0.6. "This is very surprising because spider silk is organic material," Wang said. "For organic material, this is the highest [heat conductivity] ever [measured]. There are only a few materials higher: silver and diamond."

Even more surprising, he said, is that when spider silk is stretched, thermal conductivity also goes up. Wang said stretching spider silk to its 20-percent limit also increases conductivity by 20 percent. Most materials lose thermal conductivity when stretched. That discovery "opens a door for soft materials to be another option for thermal conductivity tuning," Wang wrote in the Advanced Materials article. It could also make spider silk a valuable material for helping to create flexible, heat-dissipating parts for electronics and bandages that don't trap heat.

Wang says it is the defect-free molecular structure of spider silk, including proteins that contain nanocrystals and the spring-shaped structures connecting the proteins, that gives the material its heat-conducing properties. He said that more research needs to be done to fully understand those properties. Wang also wonders if spider silk can be modified in ways that enhance its thermal conductivity. He said the researchers' preliminary results are promising.