Fast equilibration mechanisms in disordered materials mediated by slow liquid dynamics

Area of Science:

• Physical Chemistry
• Materials Science
• Non-equilibrium Thermodynamics

Background:

• Non-equilibrium systems typically decrease free energy via molecular relaxation, dependent on density fluctuations.
• An alternative equilibration pathway with weaker temperature dependence and invariant activation energy has been experimentally observed.
• The molecular origin of this alternative pathway remained unidentified.

Purpose of the Study:

• To identify the molecular process responsible for Arrhenius-type equilibration mechanisms in liquids.
• To investigate the connection between this process and liquid dynamics, particularly in thin films.
• To determine if this process can predict equilibration rates in the glassy state.

Main Methods:

• Analysis of liquid dynamics, focusing on thin film behavior.
• Identification of a universally observed slow mode (SAP) in liquid dynamics.
• Correlation of SAP dynamics with high-temperature flow and equilibration rates.

Main Results:

• The slow-moving process (SAP) was identified as the molecular mechanism driving Arrhenius-type equilibration.
• SAP exhibits a temperature-invariant activation energy (~100 kJ mol⁻¹).
• SAP is intimately linked to high-temperature flow and efficiently drives systems towards lower energy states.

Conclusions:

• The slow-moving process (SAP) provides an alternative, temperature-independent pathway for system equilibration.
• SAP dynamics in liquids are directly connected to their ability to reach more stable states.
• Liquid dynamics measurements can serve as a predictive tool for glassy state equilibration rates.