Scientists engineer unsinkable metal tubes

University of Rochester

More than a century after the Titanic sank, engineers still have hopes of someday creating “unsinkable” ships. In a step toward reaching that lofty goal, researchers at the University of Rochester’s Institute of Optics have developed a new process that turns ordinary metal tubes unsinkable—meaning they will stay afloat no matter how long they are forced into water or how heavily they are damaged.

Chunlei Guo, a professor of optics and of physics and a senior scientist at URochester’s Laboratory for Laser Energetics, and his team describe their process for creating aluminum tubes with remarkable floating abilities in a study published in Advanced Functional Materials. By etching the interior of aluminum tubes, the researchers create micro- and nano-pits on the surface that turn it superhydrophobic, repelling water and staying dry.

When the treated tube enters water, the superhydrophobic surface traps a stable bubble of air inside the tube, which prevents the tube from getting waterlogged and sinking. The mechanism is similar to how diving bell spiders trap an air bubble to stay buoyant underwater or how fire ants form floating rafts with their hydrophobic bodies.

“Importantly, we added a divider to the middle of the tube so that even if you push it vertically into the water, the bubble of air remains trapped inside and the tube retains its floating ability,” says Guo.

Guo and his lab first demonstrated superhydrophobic floating devices in 2019, featuring two superhydrophobic disks that were sealed together to create their buoyancy. But the current tube design simplifies and improves the technology in several key areas. The disks that the researchers previously developed could lose their ability to float when turned at extreme angles, but the tubes are resilient against turbulent conditions like those found at sea.

“We tested them in some really rough environments for weeks at a time and found no degradation to their buoyancy,” says Guo. “You can poke big holes in them, and we showed that even if you severely damage the tubes with as many holes as you can punch, they still float.”

Multiple tubes can be linked together to create rafts that could be the basis for ships, buoys, and floating platforms. In lab experiments, the team tested the design using tubes of varying lengths, up to almost half a meter, and Guo says the technology could be easily scaled to the larger sizes needed for load-bearing floating devices.

The researchers also showed how rafts made from superhydrophobic tubes could be used to harvest water waves to generate electricity, offering a promising renewable energy application.