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Revisiting the Stokes-Einstein relation without a hydrodynamic diameter
Lorenzo Costigliola1, David M Heyes2, Thomas B Schrøder1
1"Glass and Time," IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark.
The Journal of Chemical Physics
|January 17, 2019
Summary
The Stokes-Einstein relation breaks down at high temperatures for Lennard-Jones fluids. Reduced diffusion and viscosity are constant along isomorphs, enabling viscosity prediction from diffusion coefficients.
Area of Science:
- Thermodynamics
- Fluid Dynamics
- Statistical Mechanics
Background:
- The Stokes-Einstein relation connects diffusion and viscosity in fluids.
- Its applicability is limited, particularly at higher temperatures and densities.
- Understanding these transport properties is crucial for characterizing fluid behavior.
Purpose of the Study:
- To investigate the breakdown of the Stokes-Einstein relation in Lennard-Jones fluids.
- To analyze diffusion coefficient and shear viscosity data across a wide temperature and density range.
- To establish a predictive relationship between diffusion and viscosity.
Main Methods:
- Analysis of diffusion coefficient and shear viscosity data for Lennard-Jones fluid.
- Examination of data along isochores above critical density.
- Evaluation of the Stokes-Einstein relation and isomorphs.
Main Results:
- The Stokes-Einstein relation shows gradual breakdown at high temperatures.
- Reduced diffusion coefficient and reduced viscosity are constant along isochores.
- A functional relationship between reduced diffusion, reduced viscosity, and temperature/density scaling was identified.
Conclusions:
- The breakdown of the Stokes-Einstein relation is linked to temperature-dependent scaling along isomorphs.
- Viscosity can be accurately predicted from the diffusion coefficient in the studied thermodynamic region.
- This work provides insights into the behavior of dense fluids.
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