Dr. James D. Martin, 919/515-3402 or email@example.com
Sally Ramey, 919/513-0300 or firstname.lastname@example.org
State Chemist Creates Structure in Amorphous Materials
chemist at North Carolina State University has
made breakthrough discoveries that advance basic
understandings of the nature of liquids and glasses
at the atomic and molecular levels. Featured in
the Sept. 26 issue of Nature, these discoveries
could lead to the development of totally new materials
with useful optical and electronic properties
- as well as applications not yet foreseen.
and glass have long been understood by scientists
to be amorphous, meaning "without structure."
Cartoon pictures in textbooks of atomic arrangements
frequently represent liquids to be much like gases,
a collection of molecules moving around randomly.
James Martin uses colorful analogies to explain
his current research.
so, according to Dr. James D. Martin, associate professor
of chemistry at NC State. "Just as a symphony is
much more than a collection of random notes, the atoms
and molecules in a liquid are quite organized - more
like those in a crystal than a gas."
this new understanding of liquid molecular organization
comes the ability to reorganize liquids.
and his colleagues have discovered the chemical principles
that allow them to essentially write new "symphonic
compositions" in amorphous materials. They have
designed the compositions and structure of several glasses
and liquids, then gone into the laboratory and made
to this new ability to design such structures, it will
be possible to engineer specific optical and electronic
properties of glasses and liquids. This amorphous-material
engineering creates the materials foundation for future
What led to this important discovery? Martin specializes
in the structure and physical properties of inorganic
materials. His work involves engineering crystals to
produce materials with desired properties.
years ago, Martin 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
first hint of the presence of structure in liquids emerged
in 1916, as scientists experimented with the X-ray diffraction
of liquids. They observed structural features indicating
some organization of molecules, but the organization
was far less than is necessary for a crystal. Since
that initial discovery, there has been significant scientific
debate about whether the structure in liquids is crystal-like
melting into a liquid, most solids undergo a very small
change in volume, suggesting that the interactions holding
molecules together in liquids, glasses and crystals
are quite similar.
these clues, scientists still have only a limited knowledge
about the structure of liquids and glasses. In a typical
freshman chemistry textbook, there are multiple pages
on gases and solids, yet only a paragraph or two on
the mystery. What is the structure of something that's
to have a structure?" Martin said. "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 like it's
possible to engineer the structure of crystals."
An analogy occurred to him as Martin stared at the crystal
models he'd made by gluing tennis balls together, and
then watched his children "swim" through big
playpens filled with plastic balls. "Picture the
balls as molecules," Martin said. "No matter
how kids may move around in the playpen, the balls always
touch each other in about the same way. And the arrangement
of the balls looks very much like my tennis-ball crystal
This new understanding of the structure of liquids and
glasses suggests the possibility of engineering new
liquids and glasses. "If you understand the network's
structure, and the chemical bonds within the structure,
you can manipulate the structure," said Martin.
"And if you change the structure, you change the
In his laboratories at NC State, Martin and graduate
student Steve Goettler have proven this by introducing
molecules of a different substance into glasses and
liquids. The foreign molecules are engineered at the
atomic level to "fit" within the liquid's
structure and interact with the liquid's own molecules.
The presence of the foreign molecules changes the liquid's
properties. Different concentrations of the foreign
molecules also change the structure, and thus produce
more changes in the liquid's properties.
To prove the structural relationships between their
amorphous materials and model crystal structures, Martin's
research group took their engineered liquids and glasses
to Argonne National Laboratory. There they are able
to look at the atomic organization of their materials
using a glass, liquids and amorphous materials diffractometer
(GLAD) instrument at Argonne's national user facility.
Martin's work, funded by the National Science Foundation,
opens a new area of scientific research: amorphous materials
engineering. He foresees the ability to control the
optical and electronic properties of glasses to produce
specialized materials that will advance optical computing
and communications technologies, among other applications.
"This new understanding," he said, "allows
us to create the materials that will be the foundation
of tomorrow's technology."
At the very least, someone will have to rewrite a lot
of chemistry textbooks.
to editors: An abstract of the Nature
intermediate-range order in amorphous materials"
Authors: James D. Martin, Stephen J. Goettler, Nathalie
Fosse, North Carolina State University; Lennox Iton,
Argonne National Laboratory
Published: Sept. 26, 2002, in Nature
Abstract: Amorphous materials are commonly understood
to consist of random organizations of molecular-type
structural units. However, it has long been known that
structural organizations intermediate between discrete
chemical bonds and periodic crystalline lattices are
present even in liquids. Numerous models - including
random networks and crystalline-type structures with
networks composed of clusters and voids - have been
proposed to account for this intermediate-range order.
Nevertheless, understanding and controlling structural
features that determine intermediate-range order in
amorphous materials remain fundamental, yet presently
unresolved, issues. The most characteristic signature
of such order is the first peak in the total structure
factor, referred to as the first sharp diffraction peak
or 'low Q' structure. These features correspond to large
real-space distances in the materials, and understanding
their origin is key to unraveling details of intermediate-range
order. Here we employ principles of crystal engineering
to design specific patterns of intermediate-range order
within amorphous zinc-chloride networks. Using crystalline
models, we demonstrate the impact of various structural
features on diffraction at low values of Q. Such amorphous
network engineering is anticipated to provide the structure/property
relationships necessary to tailor specific optical,
electronic and mechanical properties.