Significant difference in the dynamics between strong and fragile glass formers

Area of Science:

• Condensed Matter Physics
• Materials Science
• Chemical Physics

Background:

• Glass-forming liquids are classified as strong or fragile based on their dynamic behavior.
• Strong glass formers exhibit Arrhenius-like dynamics, while fragile ones show super-Arrhenius behavior.

Purpose of the Study:

• To investigate the fundamental differences in relaxation dynamics between strong and fragile glass formers.
• To link Angell's classification scheme to underlying molecular dynamics.

Main Methods:

• Molecular dynamics simulations were employed to study glass-forming liquids.
• Analysis focused on the dynamics of density fluctuations and elementary relaxation processes.

Main Results:

• Strong glass formers exhibit nondiffusive relaxation dynamics of density fluctuations.
• Fragile glass formers display diffusive relaxation dynamics.
• A key difference lies in the necessity of a density-exchange process preceding relaxation, which is absent in strong glass formers.

Conclusions:

• The study reveals a hydrodynamic distinction between strong and fragile glass formers.
• This finding offers a novel perspective on Angell's classification of glass-forming liquids.
• The elementary relaxation mechanisms directly explain the observed macroscopic dynamics.