Solving the mystery of avalanche-like change in glass Study reveals common mechanism for crystallization and aging
Researchers at the University of Tokyo have uncovered the structural origins behind the phenomenon in glasses called an "avalanche," in which particles tightly packed into a glassy solid state undergo sudden avalanche-like particle displacements resulting in the solid's transformation into a more ordered state. The group further established that the same mechanism was responsible for crystallization, such as water freezing, and the aging of glass, characterized by distortions seen in old windowpanes. The current outcome presents new design principles for stabilizing glasses that could lead to the development of new materials.
In recent years, glasses, which possess a liquid-like structure but behave like solids, have caught the attention of researchers. The research team led by Professor Hajime Tanaka, then-Project Research Associate John Russo (currently lecturer at the University of Bristol in the U.K.), and JSPS postdoctoral research fellow Taiki Yanagishima at the Institute of Industrial Science at the University of Tokyo used numerical simulation to study what are known as hard-sphere glasses, which have a large number of particles crammed together in a disordered state. The team found that rapid avalanche-like structural changes involving numerous particles begin with a small cluster of particles with large gaps between them surrounded by significantly less-ordered particles. These small particle displacements lead to a disruption in the skeletal structure supporting the mechanical balance, causing a significant cascade effect resembling an avalanche.
Glasses are solid materials possessing the properties of liquids; but they can lose many of these characteristics gradually through changes to their structure over time. Examples of some adverse effects caused by these changes include variation in the absorption rate of certain drugs, which is determined by the structure; drastic degradation of electronic properties of semiconductor materials; and ice formation in cryogenic samples, which can lead to the collapse of the internal framework of their cells. Therefore, gaining insight into how such structural change is caused and how it propagates becomes crucial in devising ways to avoid some undesirable outcomes.
"Thus far, it was unclear how a glass that apparently looks like a stable solid can crystallize and age with time. Our study shows that a loss of mechanical balance induced by the small motion of several particles triggers avalanche-like events, inducing an irreversible structural change. Therefore, this phenomenon is quite similar to a snow avalanche," says Tanaka. He continues, "We hope our finding will contribute to the stabilization of various materials and drugs in a glassy state."
Common mechanism of thermodynamic and mechanical origin for ageing and crystallization of glasses", Nature Communications Online Edition: 2017/06/29 (Japan time), doi: 10.1038/ncomms15954.
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