Spider Silk More Conductive than Copper
Xinwei Wang, Guoqing Liu and Xiaopeng Huang (left to right) analyze the thermal conductivity of spider silk. Photo by Bob Elbert.
Iowa State University associate professor Xinwei Wang has conducted experiments measuring the thermal conductivity of materials for years. After testing many of the known thermal conductors such as copper, aluminum, or diamonds, Wang wanted to find an organic material with higher-than-expected conductivity. His target candidate came in the form of spider silk—in particular, dragline thread of golden silk orbweaver spiders.
When Wang measured the silk, which is only 4 microns thick (human hair is 15 times that diameter), and was surprised by the results. In a paper just published in the Advanced Materials journal, Wang specifies that the dragline silk has a thermal conductivity of 416 watts per meter Kelvin. Copper, a well-known conductor, conducts heat at a rate of 401 watts per meter Kelvin. "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."
Wang also discovered that spider silk becomes more conductive when it is stretched; not less conductive as is the case with many materials. The conductivity rate is also directly proportional to the length: a 20 percent increase in length of the silk results in a 20 percent increase in conductivity. Wang attributes the high rate of conductivity to the pure molecular structure of the material, as well as its nanocrystal-carrying proteins and the coil-shaped structures that connect them.
Future applications of Wang's discovery might include heat-dissapating electronics, clothing, or bandages, as well as other products that prioritize thermal management. "Our discoveries will revolutionize the conventional thought on the low thermal conductivity of biological materials," Wang says.