Researchers have discovered some unique properties of spider silk that may lead to the development of new types of materials. The structure of spider silk allows certain sound frequencies through but not others, similar to an electronic band gap. The findings were just published in the journal Nature Materials.
Researchers from the United States, Europe, and Singapore collaborated in order to fully analyze the properties of spider silk. They looked at dragline strands, the threads of silk a spider uses to build the outermost sections of a web. Spiders also use dragline strands as a safety mechanism. If you’ve ever seen a spider seemingly suspended in the air, it was using a dragline strand. The researchers found that these special strands have unique acoustic properties that change depending on how much strain is placed on the thread.
The team conducted Brillouin light scattering experiments on the silk. With this technique, you can create phonons, quasiparticles of sound, and then analyze their movements within the material being tested. The researchers found that the silk could block specific sound frequencies. Interestingly, placing strain on the strand completely changed which frequencies were blocked. If the silk thread was super contracted, the bandwidth of frequencies the material blocked increased by 31%. If uncontracted, bandwidth decreased by 33%. The team also noticed a band gap of 14.8 gigahertz with a width of roughly 5.2 gigahertz when the strands were uncontracted. These properties are due to the phononic crystals present in spider silk. The crystals are joined together by softer chains. Placing varying levels of strain on the strand changes the connections of these crystals, also changing the acoustic properties of the silk.
Spider silk is unlike any currently available synthetic materials. By researching the properties of silk, scientists can potentially develop new types of material. Specifically, the authors believe their findings could lead to the development of novel sound or thermal insulation.
Dirk Schneider et al. Nonlinear control of high-frequency phonons in spider silk. Nature Materials (2016).