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Summertime means boat owners have lots of work to do, scraping their boats free of barnacles, seaweed, and other uninvited passengers. But boat paint that keeps them off also leaches poison into the seas and onto your favorite beach. As this ScienCentral News video reports, one nanotechnologist is working on better ways to repel unwanted marine hitchhikers.
Sticking It to Barnacles, and Pollution Too
When barnacles, seaweed and other marine plants and animals attach themselves to the surfaces of boats, it's called "fouling." These unwanted hitchhikers can slow down even the largest naval or commercial ships to such a degree that they need 30 percent more fuel. Marine organisms also can corrode or damage ships. Right now, small boat owners, commercial shipping lines, and the U.S. Navy try to combat fouling with paint that repels unwelcome passengers. But these paints also leach toxic metals into the seas, contaminating harbors and beaches.
For more than ten years, Christopher Ober, professor of materials science and engineering at Cornell University has been tackling the fouling problem. He starts from the point of view of a would-be foulant. "What a marine organism sees when it encounters a boat surface is something that, first of all, it wants to explore," he says. "So whether it's a simple single-cell or more complicated marine organism, it first explores the surface, and then uses a variety of tools, which we don't know much about, to decide whether it might want to settle there or not. If it chooses to settle on the surface, it actually can excrete a type of cement. Bacteria can do this; barnacles can do this; marine plants can do this."
Paint made with toxic metals does keep boats clean, but unfortunately, it also pollutes the water. Ober says that toxic metals in paint, like copper or a tin-based compound, "do remove barnacles, or do prevent barnacles from landing on a ship's surface. But these metals do accumulate in the environment and it is believed that that is a long-term hazard."
Ober is out to change all that by preventing fouling and ocean pollution at the same time. He and Sitaraman Krishnan, a member of his research team, are working on rubbery coatings made of non-toxic types of plastic. Ober adds fluorine, used to make water-repellent coatings for cookware, like Teflon. "We've designed our nanometer-thick coatings to be heavily fluorinated, and we've done it in a special way so that our materials are even more non-wetting than a material like Teflon," Ober explains. Another material he uses is polyethylene glycol (PEG). "Chemically, it's a lot like the material used to make soft contact lenses," he says. This compound also is widely used to make cosmetics and toiletries. "Just as you would paint the walls of your house with a latex plastic, we plan to coat ships with our special type of plastic."
Scraping off barnacles image: ABC News
On a plastic base, Ober's teams builds extremely thin surfaces to which marine organisms cannot attach themselves. These nanometer-thick surfaces also allow ships' hulls to clean off as they move through water. And if a ship arrives in port with any marine organisms still clinging to it, the new coating makes them very easy to remove.
One type of surface is hydrophobic. It repels water, and any would-be hitchhikers along with it. Ober compares this type of surface to the glossy paper used to back sticky labels. "The typical adhesive that a marine organism will try to extrude is based on protein, and so this protein wants to make contact with a surface that can be wettened," says Ober. "If this organism is encountering the water repellent surface, its adhesive simply can't stick very well."
Another type of surface is hydrophilic. It attracts water, and by doing so, creates an extremely thin barrier made of water between a marine organism and a ship's surface. "The marine organism encounters a structure that's almost like water itself," Ober explains. "It's so swollen with water that the organism has difficulty recognizing that it's a surface at all. So when the plant or animal's adhesive makes contact with this surface, it's a little bit like trying to glue the marine organism onto a droplet of water. Imagine trying to put a band-aid on very wet skin. It doesn't want to stick."
So far, tests of both types of Ober's new coatings have shown that any marine plant or animal that does manage to stick is far easier to clean off. His next step is to find out how long these coatings will last. He believes that his coatings also could be useful to medicine: as coatings for surgical instruments, for example, they could repel bacteria and help prevent infection.
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