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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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On the density scaling of liquid dynamics
1Naval Research Laboratory, Chemistry Division, Code 6120, Washington, DC 20375-5342, USA.
The Journal of Chemical Physics
|February 2, 2011
Summary
Superpositioning of relaxation data in liquids and polymers is explained by inverse power law (IPL) potentials. Scaling differences arise from using reduced vs. unreduced units, impacting the material constant γ.
Area of Science:
- Physical Chemistry
- Materials Science
- Statistical Mechanics
Background:
- Superpositioning of relaxation data is an experimentally observed phenomenon in liquids and polymers.
- This scaling behavior is often linked to the assumption of an inverse power law (IPL) for intermolecular potentials.
Purpose of the Study:
- To investigate the theoretical underpinnings of relaxation data superpositioning.
- To clarify the role of reduced versus unreduced quantities in scaling analysis.
- To determine the accurate relationship between scaling exponents and intermolecular potentials.
Main Methods:
- Analysis of scaling properties derived from inverse power law (IPL) liquid models.
- Comparison of scaling using reduced and unreduced thermodynamic variables (temperature, specific volume).
- Examination of the material constant γ in different scaling frameworks.
Main Results:
- Scaling of relaxation data is accurately predicted by IPL potentials.
- Discrepancies in scaling exponents at higher temperatures are attributed to the use of unreduced units.
- Only the material constant γ derived from reduced quantities directly relates to the intermolecular potential.
Conclusions:
- The inverse power law (IPL) provides a valid framework for understanding relaxation scaling in liquids and polymers.
- Careful use of reduced units is crucial for accurate determination of scaling exponents and material constants.
- The study reconciles experimental observations with theoretical models of liquid dynamics.
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