IMAGINE how great it would be if, after dinner, you could stack the greasy dishes, pots, pans and utensils in the sink and let plain old water rinse away the grime — with no help from detergents, and little or no scrubbing. Bye-bye, dishpan hands.
Plastic coatings under development may someday bring that moment to pass, rendering dinnerware, bathroom mirrors and even factory equipment sparkling clean with water alone.
The new materials may be appreciated not only by dish-washing family members, but also by environmentalists concerned about all of the soap that disappears down the drain. Detergents that end up in wastewater can cause algae to bloom, among other effects.
“We want to cut soap out of the equation for cleanup,” said Jeffrey P. Youngblood, an associate professor of materials engineering at Purdue University in West Lafayette, Ind.
In experiments, Dr. Youngblood and his colleagues attached the coatings chemically to the surface of glass. But he is now working on polymer additives for liquids that can be poured into a spray bottle, for example, and then used to clean mirrors and even eyeglasses or goggles.
Scientists call the coatings self-cleaning because, once they are applied to a surface, they do much of the work of scrubbing away oily residue — like that from a greasy fingerprint. “The oil beads up and then the water moves under the oil, lifting it up so it floats away,” said Kirsten Genson, a postdoctoral researcher in Dr. Youngblood’s group.
Getting the coating to do this is ingenious, said Michael F. Rubner, a professor of polymer materials science and engineering, and director of the Center for Materials Science and Engineering at the Massachusetts Institute of Technology. “Jeff figured out a way to have molecules on the surface that can rearrange themselves so they can self-clean, rejecting grease,” he said.
William J. Brittain, a program director at the National Science Foundation and a chemist, said Dr. Youngblood’s coatings were effective, in part because they repel oil but not water.
In the usual cleanup, soap allows oil on soiled surfaces to disperse into water as an emulsion, causing the dishwater to cloud up. But the new coatings allow water to displace oil without soap, said John Howarter, a former student of Dr. Youngblood who helped develop them and is now doing postdoctoral research at the National Institute of Standards and Technology in Gaithersburg, Md. “We get the oil to remove itself,” he said.
The self-cleaning coatings created by the Purdue team are made of polymers formed in long chains. Each part of the chain can be engineered to have a different property, said Stephen G. Boyes, an assistant professor of chemistry at the Colorado School of Mines in Golden. Here, one part has Teflon-like properties that encourage oil to bead up, and another that encourages water to wash the oil away.
The Purdue researchers have also applied the coating to filters or membranes that collect beads of oil suspended in water, but let the water itself pass through, Dr. Howarter said. Such membranes might be used in cleaning up an oil spill, for example, or for water purification.
Similar coatings might also be used on glasses, car windshields or bathroom mirrors, so that they resist fogging, as well as being easy to clean. “When you take a shower,” Dr. Genson explained, “the mirror that has our coating won’t fog up.”
Instead of forming beads, the water coats the surface in one continuous thin layer. The layer doesn’t get in the way of visibility: the mirror looks normal and clear, and people can see themselves in it.
But if it is smudged later, the smudge will be easier to remove, because it doesn’t attach directly to the mirror. “It sits on top of the surface of our coating,” she said, ready to be washed clean.
Dr. Youngblood said that he was in discussions with companies about ways to further develop the coatings and additives. “Probably we will have different permutations,” he said, depending, for example, on whether the product is for coating and cleaning windows or for treating a stain.
Here’s one suggestion for him: Come up with a permanent self-cleaning shield for our teeth. Then, in addition to dishwashing, we could eliminate another chore: daily brushing.
