An untreated piece of metal (left) sinks to the bottom, while one etched to make it superhydrophobic (right) stays afloat (Credit: University of Rochester)

Though it has been over a century since the R.M.S. Titanic sank after hitting an iceberg, modern-day ships remain as vulnerable to such catastrophes. The most recent disaster occurred in May 2019, when a sightseeing boat on the Danube River in Hungary capsized and sank after colliding with a river cruise ship, killing 28 of the 35 tourists aboard. Now, researchers from New York's University of Rochester may have found a way to avert such tragedies, with a water-repellant metal that can stay afloat even after having several holes drilled in it.

The team, led by the university's optics and physics professor Chunlei Guo, began by creating tiny grooves on a metal surface with femtosecond ‚ÄĒ one quadrillionth of a second ‚ÄĒ laser blasts. The air trapped inside the tiny etchings helped form a protective barrier around the exterior, causing water droplets to slide off. Though the technique worked for short periods, friction with the water molecules for extended amounts of time caused the metal to lose its hydrophobic ability.

To find a solution, the researchers turned to insects ‚ÄĒ specifically the Argyroneta aquatica, or diving bell spider, and the fire ant ‚ÄĒ which have both devised unique techniques to survive in water for extended periods. The arachnids, who spend their entire lives underwater, carry their oxygen supply with them inside a dome-shaped web that sits between their super-hydrophobic legs and abdomens. When the air runs out, the spiders simply return to the water's surface and create another bubble. Though fire ants do not live underwater, they are known to survive floods by linking their bodies close enough together to develop raft-like structures. This helps trap air between the insects' water-resistant limbs and allows them to stay afloat.

The insect-inspired metal stays afloat even after being punctured (Credit: University of Rochester)

The insect-inspired unsinkable metal comprises two laser-treated aluminum surfaces. Facing each other, they are connected with a small central pole at a distance carefully measured to trap the maximum amount of air. The researchers, who tested the metal's resilience by weighing it down underwater for two months, said it jumped back to the surface as soon as the load was removed. More impressively, thanks to the optimal amount of air trapped between the plates, it stayed afloat even after they drilled six holes in the plates measuring 3 mm, and one measuring 6 mm.

Though the team, who published their findings in the journal ACS Applied Materials & Interfaces on November 6th, 2019, used aluminum, they believe the "etching process" would be equally effective on other metals and other materials as well. "This could lead to an unsinkable ship, a wearable flotation device that will still float after being punctured and even electronic monitoring devices that can survive in long term in the ocean," said Guo.