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Does mesoscopic elasticity control viscous slowing down in glassforming liquids?
Geert Kapteijns1, David Richard1, Eran Bouchbinder2
1Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
The Journal of Chemical Physics
|August 22, 2021
Summary
Viscous slowing down near the glass transition is linked to mesoscopic elastic stiffness, not just macroscopic elasticity. This stiffness, κ(T), directly relates to activation barriers in some liquids, but fails in those with fragmented energy landscapes.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Computational Chemistry
Background:
- The slowing down of liquid dynamics approaching the glass transition is a key problem, with the activation energy barrier (ΔE(T)) increasing as temperature (T) decreases.
- Existing elastic models link this to macroscopic elasticity (G∞(T)) but neglect structural heterogeneity and length scales in supercooled liquids.
- These models do not fully capture the complex nature of structural relaxation in disordered materials.
Purpose of the Study:
- To investigate if mesoscopic elastic stiffness (κ(T)) controls viscous slowing down in liquids.
- To determine the relationship between mesoscopic stiffness, macroscopic elasticity, and activation energy barriers.
- To identify factors influencing the validity of the proposed mesoscopic elastic model.
Main Methods:
- Analysis of computer simulations of liquids and glasses.
- Calculation of mesoscopic elastic stiffness (κ(T)) related to inherent structures.
- Comparison of κ(T) with macroscopic shear modulus (G(T)) and activation energy barriers (ΔE(T)).
- Characterization of potential energy landscape fragmentation.
Main Results:
- Mesoscopic elastic stiffness κ(T) increases more sharply with decreasing temperature than macroscopic shear modulus G(T) in simulated liquids.
- A direct correlation (ΔE(T) ∝ κ(T)) is observed in some liquids, linking mesoscopic elasticity to energy barriers.
- This correlation fails in liquids with highly fragmented potential energy landscapes, indicating limitations of the model in such systems.
Conclusions:
- Mesoscopic elastic stiffness κ(T) offers a more relevant measure for viscous slowing down than macroscopic elasticity.
- The relationship between κ(T) and ΔE(T) highlights the importance of underlying mesoscopic properties.
- Potential energy landscape fragmentation critically affects the applicability of elastic models for structural relaxation.
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