Scientists have developed a new adaptive material that can make liquid droplets of oil and water deposited on it defy gravity or let them slide off.
The tunable composite of four layers — smooth, clear and flat in its resting state — can also change from transparent to opaque when stretched.
Engineers at Harvard’s Wyss Institute who came up with the material say it opens up the possibility of self-adjusting pipelines that can change to optimize the rate that liquids flow through them, contact lenses that clean themselves and water-repellent transparent tents that can darken to block sunlight on bright days.
A porous Teflon layer is attached to a base of elastic silicone. The Teflon is infused with a lubricating liquid that is inspired by the layer produced by tears in the eye.
"The new material is a liquid-infused elastic porous surface, which is what allows for the fine control over so many adaptive responses above and beyond its ability to repel a wide range of substances," said Wyss’s Joanna Aizenberg, the senior author of the paper describing the new material published online April 7 in the journal Nature Materials. "A whole range of surface properties can now be tuned, or switched on and off on demand, through stimulus-induced deformation of the elastic material."
So far, the team has been able to demonstrate fine control of the material’s transparency and wettability, a property of the surface to maintain contact with liquid. By stretching it, the composite material’s pores change shape, which in turn changes the surface roughness of the liquid lubricant layer. This is what causes the droplet that should be rolling down the surface to magically stop or keep going without leaving so much as a moist trail.
"It is based on a core concept: any deformation of the substrate — such as stretching, poking, or swelling — changes the size of the pores, which causes the liquid surface to change its shape," the researchers said in an announcement about their development.
Xi Yao, a Wyss postdoctoral fellow who also authored the study, said researchers would be able to alter any other property of the material that could be changed with the surface’s topography, like the ability for contaminants to adhere to it. They can also design it respond to changes in environmental conditions like temperature, light, magnetic or electric fields, chemical signals or pressure.
"This sophisticated new class of adaptive materials … have the potential to be game-changers in everything from oil and gas pipelines, to microfluidic and optical systems, building design and construction, textiles, and more," said Dr. Donald Ingber, the director of the Wyss Institute.