Despite being produced in the salivary glands of moth larvae, silk is a highly desirable material, as much for its luxuriousness as for its toughness. Now, researchers have discovered that silkworms produce silk with even more impressive mechanical properties if fed graphene or carbon nanotubes, all of which could lead to the creation of highly useful super-silks.
Graphene is a material made of sheets of carbon that are one atom thick, and as a result of its structure is about 100 times stronger than steel.
After spraying mulberry leaves with aqueous solutions of graphene or single-walled carbon nanotubes (SWNTs) and then feeding them to silkworms, scientists at Tsinghua University in Beijing found that the insects spun their cocoons with silk fibers that were much stronger than normal.
Whereas the worms’ regular silk had a toughness modulus of 22.7, those fed graphene produced silk with a toughness modulus of 38.04, while this figure rose to 48.24 for worms that ate leaves coated in SWNTs.
The silk of carbon-fed worms was also found to conduct electricity, which is quite remarkable given that normal silk does not. Detailing their work in the journal Nano Letters, the study authors explain that this is probably because the introduction of carbon compounds altered the molecular arrangement of the silk fibers so that they contained more helical than flat structures, and therefore had more movable parts.
The researchers say that this technique is more effective and environmentally friendly than trying to chemically alter the properties of silk after it has been spun, and hope to see carbon-infused silk being mass-produced in the near future.
Such a material could potentially find a wide range of applications, like manufacturing extra-strong protective clothing and environmentally friendly electronics.