Associated Press February 27, 2003

New plastic coating sheds water, may be better than a duck's back

by Randolph E. Schmid

WASHINGTON, Feb. 27 — Self-cleaning traffic signs and antennas and roofs that shed ice like water off a duck's back could be in the future thanks to a newly developed coating that is super at sending water on its way.

A team of Turkish materials researchers took the sacred lotus plant as their inspiration in developing the coating.

H. Yildirim Erbil, leader of the team that developed the plastic at Kocaeli University in Izmit, Turkey, said possible applications could range from water repellant fabrics to traffic signs, cables and even ship hulls that slice easily through the ocean.

''It was marvelous,'' said Erbil of the sight of water drops dancing across the coating surface. Their results are reported in Friday's issue of the journal Science.

Erbil said the coating should be inexpensive if it can be made on a larger scale and can have a variety of uses. But, as it is white and not transparent, it cannot be used for windows. Other water-repelling chemicals that are clear are on the market, however.

Richey M. Davis, a professor of chemical engineering at Virginia Polytechnic Institute, said the finding ''is important because it describes an elegant and simple approach to making a variety of surfaces highly nonwettable.''

''In recent years, the materials science community has come up with one example after another of engineered structures that mimic the form or the chemistry of biological structures,'' added Davis, who was not part of the research team. ''There are certainly many technologies and applications that could benefit from having a simple, inexpensive method for making a surface'' resist water.

The ability of a surface to avoid becoming wet can be increased by making it rougher, the team reported, citing as an example the leaves of the lotus plant, an aquatic perennial originally from Indonesia and India. In some Asian religions, the sacred lotus is a symbol for purity.

At very small scale — millionths of a yard — those leaves have a roughness that forms tiny air pockets, leaving water with little plant surface to stick to. Reducing the amount of plant — or plastic — that comes in contact with the water lessens the water's ability to stick.

The sacred lotus leaves have a waxy coating that the researchers studied for its self-cleaning ability to shed water and debris.
Seeking to mimic that effect, Erbil's team dissolved a commercially available plastic — isotactic polypropylene — in a solvent. Then they added a second chemical that caused the plastic to crystalize and coat a glass surface. Other surfaces could also be used, Erbil said, as long as they aren't dissolved by the solvent.

By varying the conditions the researchers were able to change the size and distribution of the plastic crystals on the surface, increasing its roughness and making it more water-resistant.

The research was curiosity driven and not backed by any industrial company, Erbil said.

The team was ''surprised and pleased'' by the result, said Erbil, a chemist who studies the physical surface of materials.

File Date: 03.01.03