New Metal Structure is Unsinkable
University of Rochester researchers, inspired by diving bell spiders and rafts of fire ants, have created a metallic structure that is so water repellent, it doesn't sink no matter how often it is forced into water or how much it is damaged or punctured.
The researchers, led by Chunlei Guo, believe that it could lead to the construction of unsinkable ships, a wearable flotation device that will still float after being punctured and electronic monitoring devices that can survive in long term in the ocean.
The structure uses a technique developed for using femtosecond bursts of lasers to “etch” the surfaces of metals with intricate micro- and nanoscale patterns that trap air and make the surfaces super-hydrophobic or water repellent.
The researchers found, however, that after being immersed in water for long periods of time, the surfaces may start to lose their hydrophobic properties. They then considered how the spiders and fire ants survive long periods under or on the surface of water by trapping air in an enclosed area. Argyroneta aquatic spiders, for example, create an underwater dome-shaped web, a so-called diving bell, that they fill with air carried from the surface between their super-hydrophobic legs and abdomens. Similarly, fire ants can form a raft by trapping air among their super-hydrophobic bodies.
Guo’s lab created a structure in which the treated surfaces on two parallel aluminum plates face inward, not outward, so they are enclosed and free from external wear and abrasion. The surfaces are separated by just the right distance to trap and hold enough air to keep the structure floating, in essence creating a waterproof compartment. The super-hydrophobic surfaces will keep water from entering the compartment even when the structure is forced to submerge in water.
Even after being forced to submerge for two months, the structures immediately bounced back to the surface after the load was released. The structures also retained this ability after being punctured multiple times, because air remains trapped in remaining parts of the compartment or adjoining structures.
Though the team used aluminum for this project, the etching process could be used for any metals.
When the Guo lab first demonstrated the etching technique, it took an hour to pattern a one-inch-by-one-inch area of surface. Now, by using lasers seven times as powerful, and faster scanning, the lab has sped up the process, making it more feasible for scaling up for commercial applications.
The project was supported by funding from the Bill & Melinda Gates Foundation, the U.S. Army Research Office and National Science Foundation.
Co-researchers include Zhibing Zhan, Mohamed ElKabbash, Jihua Zhang and Subhash Singh, all PhD candidates or postdoctoral fellows in Guo’s lab, and Jinluo Cheng, associate professor at the Changchun Institute of Optics, Fine Mechanics, and Physics in China.