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Teflon grid brings order to thin films.

The nonstick surface that made pots and pans so much easier to wash now promises to ease the jobs of chemists who seek to create well-ordered materials.

Two materials scientists have discovered they can make single crystals line up by depositing them on a very thin film of poly(tetrafluoroethylene). Better known as Teflon, the film helps orient molecules by acting as a microscopic grid, report Jean Claude Wittmann of the Charles Sadron Institute in Strasbourg, France, and Paul Smith of the University of California, Santa Barbara (UCSB).

Well-aligned crystals make materials stronger and stiffer - 100 times more so in the case of some crystalline polymers, say Smith and Wittman. Compounds also tend to conduct electricity and transmit light better when their molecules line up, notes Richard Friend of the Cavendish Laboratory in Cambridge, England.

Chemists often make polymers more ordered by spinning and stretching them under tension. But depositing them on Teflon results in a much greater degree of alignment, Smith says.

"The technique provides a particularly versatile method that will allow fabrication of ordered molecular films drawn from a wider range of materials," writes Friend in an editorial accompanying the research report in the Aug. 1 Nature. He sees the process as a boon to researchers creating molecular-sized devices for electronics.

Wittmann and Smith were studying properties of well-ordered materials when they first noticed that rubbing a piece of white Teflon on glass under the right temperature and pressure conditions, and at the right speed, left behind a very thin layer of Teflon molecules. In recent work by Helen Hansma at UCSB, atomic force microscopy revealed that these long chains lie flat on the glass, forming parallel ridges along the direction of rubbing, Smith says. Scientists studying friction had observed this tendency years earlier, he notes, but he and Wittmann were the first to realize they could use the ordered array as a template for making other films.

They can now control the temperature, pressure and deposition rate of vapors or melted material well enough to make ultrathin, nearly transparent films. Smith says he has used the thin-film grid to order many materials, including nylon, liquid crystals and polyaniline, a promising conducting polymer. Theoretically, the technique could also yield very large-area films, he adds.

But don't expect to fry up an exotic thin film in your kitchen. Teflon pans have blended, baked-on coatings whose molecules actually lack order, Smith explains.
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Title Annotation:Teflon with molecules in well-ordered rows
Author:Pennisi, Elizabeth
Publication:Science News
Date:Aug 3, 1991
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