Thermal avalanches make glasses more dynamic

Despite its apparent transparency and rigidity, glass is a complex and intriguing material. When a liquid is cooled to form a glass, its dynamics slow down significantly, resulting in its unique properties.

This process, known as the ‘glass transition’, has puzzled scientists for decades. But one of its intriguing aspects is the emergence of ‘dynamical heterogeneities’, where the dynamics become increasingly correlated and intermittent as the liquid cools down and approaches the glass transition temperature.

In a new study, researchers have proposed a new theoretical framework to explain these dynamical heterogeneities in glass-forming liquids. The idea is that relaxation in these liquids occurs through local rearrangements, which influence each other via elastic interactions. By investigating the interplay between local rearrangements, elastic interactions and thermal fluctuations, the researchers have formulated a comprehensive theory for the collective dynamics of these complex systems.

The study is a collaboration between Matthieu Wyart at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and colleagues in France and Germany. Wyart and his colleagues report their work in a paper in Physical Review X.

The team developed a ‘scaling theory’ that explains the growth of the dynamical correlation length observed in glass-forming liquids. This correlation length is linked to ‘thermal avalanches’, which are rare events induced by thermal fluctuations. These avalanches then trigger a subsequent burst of faster dynamics.

The study's theoretical framework also provides insights into the Stoke-Einstein breakdown, a phenomenon where the viscosity of the liquid becomes uncoupled from the diffusion of its particles.

To validate their theoretical predictions, the researchers conducted extensive numerical simulations in various conditions. These simulations supported the accuracy of their scaling theory and its ability to describe the observed dynamics in glass-forming liquids.

This study not only deepens our understanding of glass dynamics but also suggests a new handle on tackling the properties of some other complex systems where the dynamics are intermittent and jerky. Such dynamics are known to occur in a range of situations, from the brain's activity to the sliding between frictional objects.

“Our work connects the growth of the dynamical correlation length in liquids to avalanche-type relaxations, well studied, for example, in the context of disordered magnets, granular materials and earthquakes,” says Wyart. “As such, this approach builds unexpected bridges between other fields. Our description of how avalanches are affected by exogeneous fluctuations, including thermal ones, may thus be of more general interest.”

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.