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Updated: Dec 22, 2025
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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
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Microscopic origin of breakdown of Stokes-Einstein relation in binary mixtures: Inherent structure analysis
Shubham Kumar1, Sarmistha Sarkar1, Biman Bagchi1
1Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
The Journal of Chemical Physics
|May 3, 2020
Summary
Aqueous mixtures show surprising changes in hydrodynamic behavior due to inherent structure variations. An optimal balance of hydrogen bonds and hydrophobic interactions creates a unique ground state, explaining these phenomena.
Area of Science:
- Physical Chemistry
- Soft Matter Physics
- Computational Chemistry
Background:
- Aqueous binary mixtures often display non-ideal transport properties.
- The Stokes-Einstein relation frequently breaks down in these mixtures as composition changes.
Purpose of the Study:
- To elucidate the molecular origins of the breakdown in hydrodynamic behavior in aqueous binary mixtures.
- To identify the structural factors responsible for non-monotonic variations in transport properties.
Main Methods:
- Inherent Structure (IS) analysis to probe the energy landscape of mixtures.
- Molecular dynamics simulations using various water force fields.
- Application of Mode-Coupling Theory (MCT) for viscosity.
Main Results:
- A non-monotonic variation in average inherent structure energy correlates with the breakdown of the Stokes-Einstein relation.
- A unique ground state, stabilized by hydrogen bonding and hydrophobic interactions, exists at specific compositions.
- Isothermal compressibility exhibits a minimum at this composition, and effective hydrodynamic radius shows a sharp turnaround.
Conclusions:
- The observed hydrodynamic anomalies in aqueous mixtures are driven by inherent structural changes.
- A quasi-universal behavior is identified across different mixtures (water-dimethyl sulfoxide, water-ethanol).
- IS analysis and MCT provide a unified framework to understand the interplay between local structure and transport properties.
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