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Fractional Stokes-Einstein and Debye-Stokes-Einstein relations in a network-forming liquid
Stephen R Becker1, Peter H Poole, Francis W Starr
1Department of Physics, Wesleyan University, Middletown, CT 06459, USA.
Physical Review Letters
|October 10, 2006
Summary
The Stokes-Einstein relation breaks down in network-forming liquids like water, showing fractional behavior for both translational and rotational motion across different physical conditions.
Area of Science:
- Condensed matter physics
- Physical chemistry
- Computational fluid dynamics
Background:
- The Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) relations describe the relationship between particle size, viscosity, and diffusion in liquids.
- Network-forming liquids, such as water, exhibit complex dynamics that can deviate from these classical relations, especially at low temperatures.
- Understanding these deviations is crucial for explaining anomalous transport properties in supercooled liquids.
Purpose of the Study:
- To investigate the breakdown of the Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) relations in a prototypical network-forming liquid.
- To analyze the translational and rotational dynamics in the ST2 water model at low temperatures.
- To determine if fractional SE and DSE relations emerge and characterize their behavior across different physical regimes.
Main Methods:
- Utilizing molecular dynamics simulations of the ST2 water model.
- Analyzing particle trajectories to calculate diffusion coefficients and rotational correlation times.
- Examining the temperature dependence of transport properties and comparing them to SE and DSE predictions.
Main Results:
- Observed the ubiquitous emergence of fractional Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) relations at low temperatures.
- Found that the exponents characterizing these fractional relations are largely invariant across distinct physical regimes.
- Demonstrated that both mobile and immobile dynamical heterogeneities within the liquid adhere to the same fractional SE relation.
Conclusions:
- The breakdown of classical SE and DSE relations is a fundamental characteristic of network-forming liquids like water.
- Fractional dynamics, consistent across different liquid states and dynamical populations, govern transport properties in these systems.
- These findings offer insights into the anomalous diffusion and relaxation mechanisms in supercooled liquids.
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