Glass is a deceptively simple material, transparent and hard, but is actually very complex and intriguing. The process by which glass changes from liquid to glass is known as the "glass transition" and is characterized by a significant slowing down of the glass's dynamics, which gives the glass its distinctive properties.This transition has been a subject of scientific curiosity for years. A particularly interesting point in this process is the emergence of "dynamic heterogeneity". As a liquid cools and approaches its glass transition temperature, its dynamics become more coherent and discontinuous.
In a new study, researchers propose a new theoretical framework to explain these dynamic heterogeneities in glass-forming liquids. This view holds that relaxation in these liquids occurs through local rearrangements, which in turn influence each other through elastic interactions. Relaxation is a term in physics, which refers to the process of gradually returning from a certain state to an equilibrium state in a certain gradual physical process. By studying the interplay between local rearrangements, elastic interactions and thermal fluctuations, the researchers developed a comprehensive theory of the collective dynamics of these complex systems.
The research was carried out by Professor Matthieu Wyart of Ecole Polytechnique Fédérale de Lausanne in collaboration with colleagues from the Max Planck Institute in Dresden, the French National Academy of Sciences, the University of Grenoble Alpes and the Center for Systems Biology in Dresden. The research results have now been published in Physical Review X.
The research team proposed a "scaling theory" to explain the observed growth in dynamic correlation length in glassy liquids. This correlation length is related to "thermal collapse," a rare event induced by thermal fluctuations that subsequently triggers a faster kinetic burst.
The study's theoretical framework also provides insights into Stoke-Einstein decomposition, a phenomenon in which liquid viscosity decouples particle diffusion.
To verify their theoretical predictions, the researchers conducted extensive numerical simulations under various conditions. These simulations confirmed the accuracy of their scaling theory and its ability to describe the observed dynamics of glassy liquids.
This research not only deepens our understanding of the dynamics of glass, but also suggests a new way to address the properties of a number of other complex systems, including brain activity or the sliding between frictional objects.
"Our work links the growth of dynamic correlation lengths in liquids to collapse-type relaxation, which is well studied in disordered magnets, granular materials and earthquakes," says Matthieu Wyart. "This approach therefore creates unexpected bridges between other fields. Our description of how collapse is affected by extrinsic fluctuations, including thermal fluctuations, may therefore have broader implications."