"Here's the mystery," ruminates associate professor of chemistry Dr. James D. Martin. “What's the structure of something that's not supposed to have structure?"

Liquids and glass have long been understood by scientists to be amorphous, meaning without structure. Basic chemistry textbooks frequently present cartoon representations showing liquids to be much like gases—a collection of randomly moving atoms or molecules. But Martin has discovered a few things about the nature of liquids and glasses at the atomic and molecular levels that suggest the need to revise many of those books. Martin's breakthrough, featured in a September 2002 issue of the journal Nature, could lead to the development of totally new materials with valuable optical and electronic properties for computing and communications technologies, where the ability to direct movement of light and/or current through matter is critical.

Like many discoveries, Martin's was an unforeseen result of other basic research. Several years ago, he noticed that as he designed and synthesized crystals, he also produced a lot of liquid and glassy blobs. He originally dismissed the blobs as trash, but became curious about them because they appeared so frequently. His curiosity led him into the study of the molecular structure of liquids and glasses, an area not well understood by science.

Did the blobs have a common structure? An analogy occurred to him one day as he watched his children "swim" through big playpens filled with plastic balls. "No matter how kids moved around in the playpen, the balls always touched each other in about the same way,” Martin says. “And the arrangement of the balls looked very much like my tennis ball models of the molecules in crystals."
Martin deduced that if similar bonding interactions hold molecules in liquids, glasses and crystals, then it should be possible to engineer the structure in liquids and glasses just as it's possible to engineer the structure of crystals. And he was right. "If you understand the network's structure and the chemical bonds within the structure, you can manipulate the structure," he explains. "And if you change the structure, you change the properties."

In the lab, Martin and graduate student Steve Goettler have proven this by introducing molecules of a different substance into glasses and liquids, thereby changing the original properties. The foreign molecules were engineered at the atomic level to fit within the liquid's structure and interact with the liquid's own molecules. The presence of these foreign molecules changes the liquid's characteristics, such as the melting point, viscosity, and manner in which light travels through the material. Control of these properties is important in mechanical applications such as lubrication and liquid crystal displays.

"Just as a symphony is much more than a collection of random notes," says Martin, "the atoms and molecules in a liquid are quite organized—more like those in a crystal than a gas." With this new understanding of the structural organization in amorphous materials comes the ability to engineer specific atomic and molecular arrangements. In essence, Martin and his colleagues have discovered chemical principles that allow them to "write new symphonic masterpieces" opening a new area of scientific research—amorphous materials engineering.

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