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Materials

Joel Henry Hildebrand Award In The Theoretical & Experimental Chemistry Of Liquids

by Elizabeth K. Wilson
February 25, 2013 | APPEARED IN VOLUME 91, ISSUE 8

Ediger
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Credit: Courtesy of Mark Ediger
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Credit: Courtesy of Mark Ediger

Sponsored by ExxonMobil Research & Engineering

Though they’re technically liquids, glasses are mysterious substances in which molecules have seemingly ground to a halt in midmotion, leaving an amorphous, noncrystalline material. In addition to materials such as ordinary window glass, they can also be organic plastics, metallic alloys, or inorganic semiconductors. Over the past 20 years, the groundbreaking experiments of Mark D. Ediger, the Hyuk Yu Professor of Chemistry at the University of Wisconsin, Madison, have allowed scientists to investigate the fundamental behavior of this class of materials.

“The quest for understanding the glass transition has now become extremely active among both theorists and experimentalists, due in large part to Mark’s elegant experiments,” says James L. Skinner, chemistry professor, also at UW Madison.

Experiments performed by Ediger in the 1990s revealed an abstruse but seminal property of glassy materials known as spatially heterogeneous dynamics. Although it would be reasonable to assume that the molecules in materials approaching glass-transition temperatures should slow down uniformly, Ediger found that small collections of molecules in the materials still buzz around quickly, while neighboring clumps, only nanometers away, barely move. This strange behavior is still puzzling, but its inclusion in the framework of glassy dynamics is crucial to the field.

Theorists had predicted the spatial heterogeneity phenomenon, but Ediger’s work was the first to provide solid evidence for this behavior experimentally. Ediger’s comprehensive review on the subject has garnered nearly 1,000 citations. Spatial heterogeneity behavior is “now widely recognized as one of the canonical signatures of glassy dynamics,” notes Pablo G. Debenedetti, a chemical and biological engineering professor at Princeton University.

In 2007, Ediger’s group achieved another breakthrough: The team developed a method for preparing extremely stable glasses of organic compounds via thin-film vapor deposition. The Ediger group’s key step was to reduce the substrate temperature to 50 K below the compound’s glass-transition temperature. This allowed the deposited, vibrating molecules to rearrange at the surface and form very low energy states. By comparison, as many point out, traditional methods of simply cooling these molecules to their glass-transition temperature and waiting for all the molecules to find these low energy states would take 1,000 years.

Ediger, 55, received his bachelor’s degree in chemistry and mathematics in 1979 at Bethel College in North Newton, Kan. After receiving his Ph.D. at Stanford University in 1984, he embarked on his academic career at UW Madison, where he has remained ever since.

He is a fellow of the American Association for the Advancement of Science and the American Physical Society. His awards include the American Physical Society’s John H. Dillon Medal in 1993 and the National Science Foundation Division of Materials Research’s Special Creativity Award in 2006.

Ediger will present the award address before the ACS Division of Physical Chemistry.

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