Relation of shear viscosity and self-diffusion coefficient for simple liquids

Area of Science:

• Physical Chemistry
• Statistical Mechanics
• Fluid Dynamics

Background:

• The Stokes-Einstein relation traditionally describes diffusion of large particles in a fluid.
• Understanding shear viscosity in simple liquids requires molecular-level insights.

Purpose of the Study:

• To derive a Stokes-Einstein-type relation for the potential part of shear viscosity in simple liquids.
• To establish a connection between shear viscosity, self-diffusion, and molecular properties.

Main Methods:

• Derivation using statistical mechanics.
• Expressing shear viscosity in terms of pair correlation function, intermolecular forces, and density.
• Testing the derived formula against experimental data for noble gases (argon, krypton, xenon).

Main Results:

• A shear viscosity formula, including kinetic and potential parts, was developed.
• The formula shows good agreement with experimental viscosity for argon, krypton, and xenon at temperatures far from the triple point.
• A cutoff parameter was necessary to match experimental data near argon's triple point.

Conclusions:

• The derived Stokes-Einstein-type relation is applicable to molecular particles within the examined density and temperature ranges.
• The relationship between shear viscosity and self-diffusion provides a valuable tool for fluid property prediction.
• Deviations near the triple point highlight the influence of density fluctuations on viscosity.