AsianScientist (Aug. 11, 2017) – In a study published in Nature Communications, researchers at the University of Tokyo explain how glasses lose their liquid-like behavior during sudden avalanche-like particle displacements.
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. Their findings present design principles for stabilizing glasses that could lead to the development of new materials.
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.
To gain insight into how such structural change is caused and how it propagates, a team of researchers led by Professor Hajime Tanaka, then-Project Research Associate John Russo (currently lecturer at the University of Bristol in the UK), and JSPS postdoctoral research fellow Dr. 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.
“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,” said Tanaka.
“We hope our finding will contribute to the stabilization of various materials and drugs in a glassy state,” he said.
The article can be found at: Yanagishima et al. (2017) Common Mechanism of Thermodynamic and Mechanical Origin for Aging and Crystallization of Glasses.
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Source: University of Tokyo.
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