Moving in sync, slowly, in glassy liquids

Tokyo, Japan – Glass might seem to be an ordinary material we encounter every day, but the physics at play inside are actually quite complex and still not completely understood by scientists. Some panes of glass, such as the stained-glass windows in many Medieval buildings, have remained rigid for centuries, as their constituent molecules are perpetually frozen in a state of disorder. Similarly, supercooled liquids are not quite solid, in the sense that their fundamental particles do not stick to a lattice pattern with long-range order, but they are also not ordinary liquids, because the particles also lack the energy to move freely. More research is required to reveal the physics of these complex systems. 

Now, in a study published in Nature Materials, researchers from Institute of Industrial Science, The University of Tokyo used advanced computer simulations to model the behavior of fundamental particles in a glassy supercooled liquid. Their approach was based on the concept of the Arrhenius activation energy, which is the energy barrier a process must overcome to proceed. One example is the energy required to rearrange individual particles in a disordered material. “Arrhenius behavior” means that a process needs to rely on random thermal fluctuations, and the rate exponentially decreases as the energy barrier gets larger. However, situations that require cooperative rearrangement of particles may be even more rare, especially at low temperatures. These are sometimes called super-Arrhenius relationships.

The new study was the first to demonstrate the relationship between the structural order and dynamic behavior of liquids at a microscopic level. “Using numerical analysis within a computer model of glass-forming liquids, we showed how fundamental particle rearrangements can influence the structural order and dynamic behavior,” the lead author of the study Seiichiro Ishino says. The team demonstrated that a process they call “T1”, which maintains the order formed within the liquid, is the key to understanding cooperative dynamics. If a T1 process disrupts local structural order, it must involve the independent motion of particles, which results in normal Arrhenius-like behavior. By contrast, if the T1 rearrangement maintains local order in a cooperative manner, its influence spreads outward, leading to super-Arrhenius behavior.

“Our research offers us a new microscopic perspective on the long-sought origin of dynamic cooperativity in glass-forming substances. We anticipate that these findings will contribute to better control of material dynamics, leading to more efficient material design and enhanced glass manufacturing processes,” senior author Hajime Tanaka says. This may include stronger and more durable glass for smartphones and other applications.

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The article, “Microscopic structural origin of slow dynamics in glass-forming liquids,” was published in Nature Materials at DOI:10.1038/s41563-024-02068-8.

About Institute of Industrial Science, The University of Tokyo

The Institute of Industrial Science, The University of Tokyo (UTokyo-IIS) is one of the largest university-attached research institutes in Japan. UTokyo-IIS is comprised of over 120 research laboratories—each headed by a faculty member—and has over 1,200 members (approximately 400 staff and 800 students) actively engaged in education and research. Its activities cover almost all areas of engineering. Since its foundation in 1949, UTokyo-IIS has worked to bridge the huge gaps that exist between academic disciplines and real-world applications.