Researchers at the University of Rochester in the state of New York, USA, have created a new metallic structure which, they say, is so water-repellent it won't sink – no matter how often it is forced into water or how much it is damaged or punctured.
The team are confident the new metal could lead to the construction of “unsinkable ships, wearable flotation devices, and ocean monitoring equipment”.
They developed a groundbreaking technique using femtosecond bursts of lasers to ‘etch’ the surfaces of metals with intricate micro- and nanoscale patterns that trap air and make the surfaces superhydrophobic, or water repellent.
However, they found that after being immersed in water for long periods of time, the surfaces started to lose their hydrophobic properties.
As they tried to find a solution, inspiration struck them when they considered the life habits of aquatic spiders that can survive for long periods under water by creating dome-shaped webs – so-called diving bells – which they fill with air carried from the surface between their super-hydrophobic legs and abdomens.
“It was a very timely observation,” explains Chunlie Guo, professor of optics and physics at the University of Rochester, who led the research.
“The key insight was that multifaceted superhydrophobic (SH) surfaces can trap a large air volume – which points towards the possibility of using SH surfaces to create buoyant devices.”
Guo’s team went on to create a structure in which the treated surfaces on two parallel aluminium plates face inward, not outward – so that they are enclosed and free from external wear and abrasion.
The surfaces are then separated by an exactly calculated distance to trap and hold enough air to keep the structure floating, by creating a waterproof compartment.
The superhydrophobic surfaces keep water from entering the compartment even when the structure is forced to submerge in water.
“Even after being submerged for two months, the structures immediately bounced back to the surface after the load was released,” says Guo.
“The structures retained this ability even after being punctured multiple times, because air remains trapped in remaining parts of the compartment or adjoining structures.
“Although we used aluminium for this development, we believe that the technique could be used for many other metals or materials.”