Does mesoscopic elasticity control viscous slowing down in glassforming liquids?

Abstract

The dramatic slowing down of relaxation dynamics of liquids approaching the glass transition remains a highly debated problem, where the crux of the puzzle resides in the elusive increase of the activation barrier $\Delta E(T)$ with decreasing temperature $T$. A class of theoretical frameworks -- known as elastic models -- attribute this temperature dependence to the variations of the liquid's macroscopic elasticity, quantified by the high-frequency shear modulus $G_{\infty }(T)$. While elastic models find some support in a number of experimental studies, these models do not take into account the spatial structures, length scales, and heterogeneity associated with structural relaxation in supercooled liquids. Here, we propose that viscous slowing down is controlled by a mesoscopic elastic stiffness $\kappa (T)$, defined as the characteristic stiffness of response fields to local dipole forces in the liquid's underlying inherent states. First, we show that $\kappa (T)$ -- which is intimately related to the energy and length scales characterizing quasilocalized, nonphononic excitations in glasses -- increases more strongly with decreasing $T$ than the macroscopic inherent state shear modulus $G(T)$ in several computer liquids. Second, we show that the simple relation $\Delta E(T)\propto \kappa (T)$ holds remarkably well for some computer liquids, implying a direct connection between the liquid's underlying mesoscopic elasticity and enthalpic energy barriers. On the other hand, we show that for other computer liquids, the above relation fails. Finally, we provide strong evidence that what distinguishes computer liquids in which the $\Delta E(T)\propto \kappa (T)$ relation holds, from those in which it does not, is that the latter feature highly granular potential energy landscapes, where many sub-basins separated by low activation barriers exist. [Rest of abstract abridged]

15 pages, 12 figures. Accepted manuscript

References in corpus (22)

• Theoretical perspective on the glass transition and amorphous materials
• Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder
• Supercooled Liquids for Pedestrians
• Glassy dynamics of kinetically constrained models
• Irreversible reorganization in a supercooled liquid originates from localised soft modes
• The role of local structure in dynamical arrest
• Identifying structural flow defects in disordered solids using machine learning methods
• Understanding fragility in supercooled Lennard-Jones mixtures. I. Locally preferred structures
• The Relationship Between Local Structure and Relaxation in Out-of-Equilibrium Glassy Systems
• Geometric interpretation of pre-vitrification in hard sphere liquids
• Heterogeneous Dynamics, Marginal Stability and Soft Modes in Hard Sphere Glasses
• Finite-temperature critical point of a glass transition
• The instantaneous shear modulus in the shoving model
• Nonlinear modes disentangle glassy and Goldstone modes in structural glasses
• Elastoplasticity Mediates Dynamical Heterogeneity Below the Mode-Coupling Temperature
• Mechanical disorder of sticky-sphere glasses. I. Effect of attractive interactions
• A Microscopic Theory of Softness in Supercooled Liquids
• Mechanical disorder of sticky-sphere glasses. II. Thermo-mechanical inannealability
• A Theory of Localized Excitations in Supercooled Liquids
• Revisiting the Concept of Activation in Supercooled Liquids
• The Devil is in the details: Pentagonal bipyramids and dynamic arrest
• Unifying framework for strong and fragile liquids via machine learning: a study of liquid silica