The new materials are inspired by the colour-changing, shape-shifting properties of octopus skin. Credit: Ethan Daniels/Alamy
Researchers have created the first materials that can change not just their colour, but also their surface texture on demand — inspired by how octopuses adjust their skin to blend in with the rocks they sit on. The artificial ‘skin’ can switch from matte to shiny and display a variety of other effects, before reverting back to its initial state. The results were published today in Nature1.
Bumps or grooves of a range of sizes — from the sub-micrometre scales of visible-light wavelengths 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.
Patterns made on thin polymer films using an electron beam affect how the texture of the surface changes when exposed to water.Credit: Siddharth Doshi, Neerav Soneji, Katie Richards
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 capable of absorbing varying amounts of water, producing a ‘landscape’ of bumps on the surface. The result was materials that could drastically change their appearance when wet. When 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.
Unique applications
The group’s demonstrations are “quite unique”, and open the door to creating consumer products or buildings that can change their appearance on demand and in unprecedented ways, says Philippe Lalanne, a nanophotonics researcher at the Aquitaine Institute of Optics in Talence, France.