Structural relaxation in a system of dumbbell molecules

Area of Science:

• Condensed matter physics
• Theoretical chemistry
• Statistical mechanics

Background:

• Glassy dynamics describe the slow relaxation of disordered materials.
• Mode-coupling theory (MCT) is a powerful framework for understanding these dynamics.
• Molecular shape, specifically elongation, can significantly influence material properties.

Purpose of the Study:

• To investigate the impact of molecular elongation on glassy dynamics using MCT.
• To analyze relaxation behavior and transport properties in systems of symmetric dumbbells.
• To identify universal scaling laws and deviations from them based on molecular shape.

Main Methods:

• Utilizing mode-coupling theory (MCT) for the evolution of glassy dynamics.
• Calculating interaction-site-density-fluctuation correlators.
• Analyzing dipole-relaxation functions and mean-squared displacements.

Main Results:

• For large molecular elongations, universal relaxation laws near the glass transition are observed, similar to hard-sphere systems.
• Rotation-translation coupling extends the crossover interval in mean-squared displacement for constituent atoms.
• For small elongations, the superposition principle for reorientational alpha processes is violated, and relaxation scales decouple.

Conclusions:

• Molecular elongation is a critical factor governing glassy dynamics and relaxation behavior.
• Deviations from universal laws and decoupling of relaxation processes occur for small elongations.
• The findings provide insights into structure-property relationships in glassy materials.