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Weaving a tapestry of spiral chemical waves.

Oscillating chemical reactions display a rich repertoire of moving patterns. Waves of color in the shape of spirals and concentric rings drift gracefully through thin liquid films, moving in sync with the periodic rise and fall in the concentrations of the chemicals involved.

But the sights are even more spectacular when two sets of chemical waves interact. "This kind of chemistry is very pleasing to the eye," says chemist Kenneth Showalter of West Virginia University in Morgantown. "There's a tremendous richness here to explore."

To study how chemical waves interact, Showalter and his co-workers watch the formation of patterns on both surfaces of a thin polymer membrane stretched out like a drumhead and immersed in a solution-filled reaction vessel. The solution contains the ingredients for a widely studied oscillating chemical system known as the Belousov-Zhabotinsky reaction (SN: 7/1/89, p.6).

By loading the membrane with ferroin, an iron-containing catalyst, the researchers ensure that the reaction takes place only on the membrane surfaces rather than in the solution. As the stirred chemical reagents swirl past each surface, they react to produce the distinctive red and blue bands characteristic of this reaction. The membrane's transparency allows the researchers to see the two chemical wave patterns superimposed on each other.

The membrane also acts as a kind of gatekeeper, allowing only certain chemical species to pass through. Thus, the wave pattern formed on one side of the membrane initially appears quite independent of that formed on the other. But over several hours, the two patterns evolve in such a way as to indicate that they somehow "feel" each other, Showalter and his colleagues observe.

This coupling of the two sets of chemical waves produces a geometrical complexity not seen in the patterns formed by a single set of waves. At first, the coupling spontaneously gives rise to spiral waves. More complex, irregular patterns often appear at later stages. Eventually, the two waves become synchronized in time and space.

Such studies may offer insights into the chemical communication that occurs across biological cell membranes, Showalter says. He and his co-workers describe their experiments in the May 9 NATURE.
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Title Annotation:how chemical waves interact
Author:Peterson, Ivars
Publication:Science News
Date:May 18, 1991
Words:356
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