Many water-hoarding materials exist in nature, such as the leaves of certain plants and the backs of desert beetles. Incredibly, spider silk also has a structure that is perfectly adapted to water collection.
In 2010, a team of Chinese researchers published a paper in the journal Nature revealing important details of this structure. The scientists showed that when spider silk gets wet, rough-textured bumps start to form along the otherwise smooth fibre of the silk. The difference in the texture of the silk creates differences in pressure and energy that drive water towards the bumps, enhancing the silk’s water-collecting ability.
This is why we see water clinging to a spider’s web in distinct droplets, with the bumps – or what the scientists called ‘spindle knots’ – acting as collection sites.
The challenge now is to create cheap, bio-inspired materials that mimic the structure of natural spider silk to harvest moisture from fog in dry regions. The materials, which are designed by Prof Yongmei Zheng and her team at Beihang University, are made by dip-coating a smooth artificial fibre in a polymer fluid that breaks up and dries to form the bumps, that are so crucial to the structure.
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