Physicists shatter stubborn mystery of how glass forms
A physicist at the University of Waterloo is among a team of scientists who have described how glasses form at the molecular level and provided a possible solution to a problem that has stumped scientists for decades.
Their simple theory is expected to open up the study of glasses to
non-experts and undergraduates as well as inspire breakthroughs in novel
nano materials.
The paper published by physicists from the University of Waterloo,
McMaster University, ESPCI ParisTech and Université Paris Diderot
appeared in the journal, Proceedings of the National Academy of Sciences (PNAS).
Glasses are much more than silicon-based materials in bottles and
windows. In fact, any solid without an ordered, crystalline structure --
metal, plastic, a polymer -- that forms a molten liquid when heated
above a certain temperature is a glass. Glasses are an essential
material in technology, pharmaceuticals, housing, renewable energy and
increasingly nano electronics.
"We were surprised -- delighted -- that the model turned out to be so
simple," said author James Forrest, a University Research Chair and
professor in the Faculty of Science. "We were convinced it had already
been published."
The theory relies on two basic concepts: molecular crowding and
string-like co-operative movement. Molecular crowding describes how
molecules within glasses move like people in a crowded room. As the
number of people increase, the amount of free volume decreases and the
slower people can move through the crowd. Those people next to the door
are able to move more freely, just as the surfaces of glasses never
actually stop flowing, even at lower temperatures.
The more crowded the room, the more you rely on the co-operative movement with your neighbors to get where you're going.
Likewise, individual molecules within a glass aren't able to move
totally freely. They move with, yet are confined by, strings of weak
molecular bonds with their neighbors.
Theories of crowding and cooperative movement are decades old. This
is the first time scientists combined both theories to describe how a
liquid turns into a glass.
"Research on glasses is normally reserved for specialists in
condensed matter physics," said Forrest, who is also an associate
faculty member at Perimeter Institute for Theoretical Physics and a
member of the Waterloo Institute for Nanotechnology. "Now a whole new
generation of scientists can study and apply glasses just using
first-year calculus."
Their theory successfully predicts everything from bulk behaviour to
surface flow to the once-elusive phenomenon of the glass transition
itself. Forrest and colleagues worked for 20 years to bring theory in
agreement with decades of observation on glassy materials.
An accurate theory becomes particularly important when trying to
understand glass dynamics at the nanoscale. This finding has
implications for developing and manufacturing new nanomaterials, such as
glasses with conductive properties, or even calculating the uptake of
glassy forms of pharmaceuticals.
Story Source:
The above post is reprinted from materials provided by University of Waterloo. Note: Materials may be edited for content and length.
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