Materials Physicists Attracted to Spider Webs
By Eric Betz
Among the many breakthroughs in materials science presented at this year’s March Meeting, it was hard not to be drawn in by a physicist claiming to have figured out the physics of spider webs.
If you were a fly, freeing yourself from a spider web would be an insurmountable task, but why the spider’s glue is so sticky has been an unsolved mystery. Even in wet weather, the spider’s natural net is often the end for a non-observant insect. And according to Vasav Sahni of the University of Akron, studying what makes spider webs sticky could lead to myriad adhesive applications.
Sahni is tight-lipped about what his team is currently developing, but in a press conference at the meeting, he discussed how his team was able to replicate the spider’s glue in his lab.
Sahni said that spider webs are made from two different types of silk. The first type is called dragline silk, which makes up the radial lines going from the outer edges of the web toward the center. The second type is called capture silk, and these lines are responsible for absorbing momentum when the prey collides with the web. However, the soft and highly sensitive capture silk must also ensure that they prey is caught and can’t get away after impact.
These lines have a silk core with tiny water and polymer nodules dispersed along them. Sahni and his colleagues set out to find exactly how these nodules behaved so that they could mimic the system.
To do that, they met in their lab at night so as to avoid any tiny vibrations that might be created by their coworkers. “If you breathe, you can see it on the force sensor,” said Sahni.
They inserted a custom glass probe into the tiny glue droplets and measured the force needed to stretch one individually. They determined that the nodules behave like a viscoelastic solid and then used that information to create their own spider glue. Sahni said the technology could be used for everything from underwater sealants to in-body sutures.
Among the other materials advances at the meeting was a presentation by Tobin Filleter of Northwestern University on a new fabric made by weaving together carbon nanotubes. Filleter said that scaling carbon nanotubes up into larger structures has been difficult so far, but he thinks his team may have found a solution.
By irradiating fibers of carbon nanotubes with an electron beam, Filleter was able to induce crosslinking between the fibers and cause them to bundle into a much tougher carbon nanotube twine. His next step is to try to produce a macroscopic yarn, and if his methods hold up, Filleter said it could lead to some of the toughest textiles ever made.
Ming Xu, a researcher from the National Institute of Advanced Industrial Science and Technology in Japan, also demonstrated a new rubber-like material that she and her colleagues were developing, which is capable of withstanding a record range of temperatures. Xu said the viscoelastic material is made entirely of carbon nanotubes and that a sample withstood her team shooting metal spheres at it while they exposed it to temperatures ranging from -196 C to 1000 C.
Xu said the ultimate applications were unknown, but that it could be used in anything from spacecraft to earthquake retrofitting.