Glass-forming liquid dynamics can be accurately modeled by a simple model of disordered solids
Glass-forming liquid dynamics can be accurately modeled by a simple model of disordered solids lead image
The fluidity of glass-forming liquids has only recently begun to be understood. To the surprise of the glass community, the random barrier model (RBM) – built as an idealized model of disordered solids – was recently shown to universally describe the dynamics of glass-forming liquids. Inspired by these experimental findings, Thomas Schrøder and Jeppe Dyre computationally investigated the low-temperature dynamics of a viscous model system.
“The time and frequency dependency of relaxation and transport quantities is one of the key routes to insight into the mystery of viscous liquid dynamics,” said Schrøder. “The fact that experimental results found that these liquids are well described by a model with frozen disorder was very surprising, and we simply had to investigate this.”
The authors introduced a crystallization-resistant computer liquid, which they used to confirm the RBM accurately describes the system’s behavior without including any shape parameters. Typically, the time dependence of the system’s mean-square displacement (MSD) is used as a standard examination of its dynamics, but the MSD varies for different liquids. This nonuniversality is in contradiction to the RBM.
By utilizing a modified version of the MSD, the authors normalized the data to account for a plateau that occurs as a result of the short-term cage rattling of particles. This reconciles RBM with MSD and explains the differences in universality. If the plateau is nonuniversal, the MSD is also nonuniversal.
“We do not believe that the level of agreement we see between the inherent MSD and the RBM with zero shape parameters happens by coincidence,” Schrøder said. “We do not understand why this is the case, but there are possibly important insights into the dynamics of viscous glass-forming liquids to be found.”
Source: “Solid-like mean-square displacement in glass-forming liquids,” by Thomas B. Schrøder and Jeppe C. Dyre, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0004093 .
