Nature reports on materials engineers stealing the secrets of octopus skin to create substances that can change color and texture on demand:
Very small sub-micrometre bumps or grooves, comparable in size to visible-light wavelengths, and larger ones up to millimetres affect how a surface scatters light. This can make a material more or less dull, or change its colour when observed from different angles. Molluscs, such as octopuses and cuttlefish, use tiny muscles embedded in their skin to produce these effects for camouflage or communication.
Siddharth Doshi, a materials scientist at Stanford University in California, and his collaborators built what they call metasurfaces out of PEDOT:PSS, a type of polymer that has been used in solar panels and printable electronics. They chose the material because it swells on contact with water, but in a reversible way: it will release the water and shrink when exposed to other liquids, such as certain alcohols.
To create materials with a controllable texture, the researchers put a layer of the polymer on a substrate and used an electron beam to create regions that can absorb varying amounts of water, producing a ‘landscape’ of bumps on the surface. The result was materials that could drastically change their appearance when wet. To be used practically, the surfaces could be covered by a transparent film — allowing the flow of water to be controlled, or for water to be mixed with varying concentrations of the alcohol 2-propanol. “Just applying the alcohol is enough to squeeze the water out,” says Doshi.
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Video at the link.