Metastable Lennard-Jones fluids. I. Shear viscosity

Area of Science:

• Thermodynamics
• Fluid Dynamics
• Computational Physics

Background:

• Understanding fluid viscosity is crucial for many physical and chemical processes.
• Accurate viscosity data, especially in metastable regions, is essential for theoretical models.

Purpose of the Study:

• To calculate the coefficient of shear viscosity (η(s)*) for a Lennard-Jones fluid using molecular dynamics.
• To develop a comprehensive equation describing viscosity's temperature and density dependence in both stable and metastable states.
• To investigate fluid behavior near phase transition boundaries and assess the Stokes-Einstein relation's applicability.

Main Methods:

• Employed molecular dynamics simulations.
• Performed calculations across a wide range of reduced temperatures (0.4–2.0) and densities (0.01–1.2).
• Obtained viscosity values for 217 thermodynamic states, including metastable regions.

Main Results:

• Calculated shear viscosity for 217 states, with 99 in metastable liquid and gas regions.
• Achieved satisfactory agreement with existing data for stable thermodynamic states.
• Developed a novel equation accurately describing viscosity across stable and metastable regions up to nucleation boundaries.
• Discussed viscosity behavior near the spinodal and examined the Stokes-Einstein relation at high supercoolings.

Conclusions:

• The developed equation provides a robust model for Lennard-Jones fluid shear viscosity, encompassing stable and metastable states.
• Molecular dynamics is effective for studying fluid properties in challenging thermodynamic regimes.
• Further research is needed to fully understand transport phenomena near critical points and spinodal limits.