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Chandler reports breakthough in solving the puzzle of glass

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David Chandler
David Chandler

If you could zoom in on the atomic-level structure of water, you could easily tell whether it was in its liquid or solid state. As a liquid, the molecules of water are jumbled up, compared to the orderly crystalline pattern of ice.

But if you were to zoom in on the atoms of molten and solid glass, you would have a hard time knowing which was which. "Like molten glass," says chemistry professor David Chandler, "solid glass is a jumble of molecules without an orderly crystalline pattern. So what makes it a solid? We don't know the entire answer, but we have discovered an important part of it."

Along with colleague Juan P. Garrahan of the University of Nottingham, England, the Chandler group has published a paper entitled "Dynamic Order-Disorder in Atomistic Models of Structural Glass Formers." In addition to Garrahan and Chandler, co-authors include current Chandler postdoc Lester Hedges and former Chandler postdoc Robert Jack of The University of Bath, England. The paper is available on-line through Science Express, which provides electronic publication of selected Science magazine papers in advance of print.

The Romans brought glassmaking to England around 55 BCE, but nature has been making forms of glass for billions of years. In what is now the United States, Native Americans chipped arrowheads from obsidian, a glassy material formed when molten lava cooled too quickly to form a crystalline structure. The black sand beaches of the island of Hawaii are formed from lava that spills into ocean, shatters as it suddenly cools, and eventually washes up onshore as small glassy pebbles.

Says Hedges, "Many people are under the mistaken impression that because glass lacks a crystalline structure, it's not really a solid, but some sort of super slow-motion liquid. They point to the unevenness of window glass in old buildings as evidence that the glass has been slowly flowing over decades or centuries. But the unevenness of old glass comes from crude manufacturing techniques. It really is a solid, although one with unusual properties."

For over a century, principles of thermodynamics have aided the design of ordered solids, materials like steel and aluminum alloys. No similar principles have been discovered for the production of glassy solids. But Chandler and colleagues have made a significant step towards developing such principles, and they did so not through experiments (which are difficult to conduct on solidifying glass) but through theory and the use of computers.

In effect, the researchers were able to theoretically simulate the process of melting and hardening glass. They have created complex computational techniques that allow them to model glass as it passes through the phase change from liquid to solid.  It proves to be an unusual phase change, one that becomes apparent only when viewed in both space and time.

"Now that we have a better sense of what to look for," says Chandler, "we hope to work with the experimenters to find protocols for collecting empirical data to verify the phase transition phenomena described in our work."

Ultimately, understanding the glass transition is important because the principles governing it can guide scientists and engineers towards methods for producing longer lasting and stronger varieties of glass — materials that affect our lives everyday, from windows to kitchen equipment, from optical lenses to plastics to ceramics.

More Information

Science Express
Chandler Research Group

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