From fluctuating entropic neck to Rosenfeld-Adam-Gibbs crossover dynamics in supercooled liquids

Area of Science:

• Condensed Matter Physics
• Theoretical Chemistry
• Statistical Mechanics

Background:

• Supercooled liquids show dynamical slowdown with temperature changes.
• Transport dynamics transition from collision-dominated to activated relaxation.
• This transition is linked to Rosenfeld excess-entropy and Adam-Gibbs scaling.

Purpose of the Study:

• Develop a unified theoretical framework for supercooled liquid dynamics.
• Explain the crossover from high-temperature to low-temperature transport behavior.
• Provide a semi-microscopic interpretation of the observed phenomena.

Main Methods:

• Utilized a memory-function formalism.
• Extended Zwanzig's entropic-neck picture to configuration space.
• Derived a reduced description from coupled slow coordinates (intra-basin motion and inter-basin escape).

Main Results:

• Developed a model where transport occurs via entropically constrained pathways connecting metastable basins.
• Showed dynamic coupling between intrabasin and transition coordinates, creating a nonseparable memory kernel.
• Recovered Rosenfeld scaling at high temperatures and Adam-Gibbs dynamics at low temperatures due to an entropic bottleneck.

Conclusions:

• The entropic-neck mechanism unifies transport dynamics across temperature regimes in supercooled liquids.
• The framework explains the crossover behavior and its relation to mode-coupling theory.
• The model extends to nonequilibrium conditions, explaining fictive temperature evolution and fragility.