Relation between concentration fluctuations and dynamical heterogeneities in binary glass-forming liquids: A...

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Physics

Background:

• Binary liquids with high dynamical contrast are crucial for understanding glass formation.
• Concentration fluctuations and microphase segregation are key phenomena in such mixtures.
• The relationship between concentration fluctuations and molecular dynamics, particularly glassy slowdown, requires further investigation.

Purpose of the Study:

• To investigate the molecular dynamics of binary glass-forming liquids with significant dynamical asymmetry.
• To explore the role of concentration fluctuations and microphase segregation in the glassy slowdown of these mixtures.
• To elucidate the anomalous dynamics observed in the fast-moving component of the binary liquid.

Main Methods:

• Molecular dynamics simulations were employed to model binary glass-forming liquids.
• Mixtures of water-like molecules with varying polarities and distinct dynamics were simulated.
• Analysis focused on concentration fluctuations, component dynamics, and particle mobility as a function of temperature and composition.

Main Results:

• Concentration fluctuations grow significantly upon cooling, indicating an impending mixing-demixing phase transition.
• Component dynamics decouple significantly at low temperatures, with the slow component resembling neat glass formers.
• The fast component exhibits anomalous dynamics, including sub-linear diffusion and quasi-logarithmic correlation decays, explained by concentration-dependent mobility and microphase segregation.

Conclusions:

• Growing concentration fluctuations and microphase segregation drive spatially heterogeneous dynamics in binary liquids.
• The slow component stabilizes microphase segregation, while the fast component navigates concentration and mobility gradients.
• These findings provide a framework for understanding glassy slowdown in binary liquids, including aqueous solutions, driven by dynamical asymmetry and concentration effects.