Why nature thinks bigger is better

IOWA STATE (US) — In a new paper, a team of scientists sheds light on coarsening, the natural process during which “the big get bigger.”

Coarsening happens when a group of objects of different sizes transforms into fewer objects with larger average size. Examples include the geologic formation of gemstones, the degradation of pharmaceutical suspensions, and the manufacture of structural steels.

To illustrate the concept, Patricia Thiel of Iowa State University and the U.S. Department of Energy’s Ames Laboratory puts a box of tissues to the right, a stack of coasters in the middle, and a trinket box to the left.

“Nature,” she says, “doesn’t want lots of little things.” So Thiel grabs the smaller things and slides them into a single pile next to the bigger tissue box. “Nature wants one big thing all together, like this.”

Thiel and colleagues have been using scanning tunneling microscope technology—an instrument that allows them to see individual atoms—to study how coarsening happens on the surface of objects. Their work is reported in the Oct. 29 issue of the journal Science.


They’ve studied nanoscale particles grown on the surface of silver and how adding sulfur can increase coarsening. They’re trying to learn the mechanism of that increase and understand the nature of the messengers that move atoms during the coarsening process.

What the researchers are looking for is a general principle that explains what they call additive-enhanced coarsening. To do that, Thiel says, they still need to collect and analyze data from more coarsening systems.

James Evans, an Iowa State professor of physics and astronomy and a faculty scientist for the Ames Laboratory, says a better understanding of the coarsening process can help researchers develop small structures—including nanoscale technologies, catalysts, or drug suspensions—that resist coarsening and are therefore more durable.

A better understanding could also help researchers manipulate coarsening to develop structures with a very narrow distribution of particle sizes, something important to some nanotechnologies.

“When we’re building something on a small scale, for it to be useful, it has to be robust, it has to survive,” Evans says. “And one thing we’re looking at is the stability of the very tiny structures that are crucial to nanoscale technologies.”

The work was supported by the National Science Foundation.

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