The new material is inspired by the color-changing and shape-changing properties of octopus skin. Credit: Ethan Daniels/Alamy
Researchers have created the first materials that can change not only their color but also their surface texture on command, inspired by how octopuses adjust their skin to blend in with the rocks they sit on. Artificial “skin” can go from matte to shiny and display a variety of other effects, before returning to its initial state. The results were published today in nature1.
Bumps or grooves of different sizes — from sub-micrometer scales of visible light wavelengths down to millimeters — affect how a surface scatters light. This can make the material more or less faint, or change color when observed from different angles. Molluscs, such as octopuses and squid, use small 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 have built what they call metasurfaces from 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 the opposite way: it will release water and shrink when exposed to other liquids, such as some alcohols.
Patterns made on thin polymer films using an electron beam affect how the surface texture changes when exposed to water.Credit: Siddharth Doshi, Nirav Soneji, Katie Richards
To create materials with a controllable texture, the researchers placed a layer of polymer on a substrate and used an electron beam to create areas capable of absorbing varying amounts of water, creating “landscapes” of bumps on the surface. The result was materials that could radically change their appearance when wet. When used in practice, surfaces can be covered with a transparent film, allowing control of water flow, or mixing of water with different concentrations of 2-propanol alcohol. “Just applying alcohol is enough to get the water out,” says Doshi.
Unique applications
Philippe Lalanne, a nanophotonics researcher at the Aquitaine Institute of Optics in Talens, France, says the group’s demonstrations are “completely unique” and open the door to creating consumer products or buildings that can change their appearance on demand, in unprecedented ways.