Diffusion in Multicomponent Liquids: From Microscopic to Macroscopic Scales.

Area of Science:

• Physical Chemistry
• Thermodynamics
• Transport Phenomena

Background:

• Aqueous alcohol mixtures exhibit microscopic inhomogeneity, yet their transport properties are understudied.
• Complex intermolecular interactions, including hydrogen bonding, make analyzing these mixtures challenging.

Purpose of the Study:

• To investigate diffusion in the ternary mixture of water, methanol, and ethanol.
• To develop and apply a novel protocol for comparing diffusion coefficients from molecular simulation and Taylor dispersion experiments.
• To critically analyze transport processes in multicomponent aqueous alcohol mixtures.

Main Methods:

• Molecular simulation techniques were employed to study diffusion on a microscopic scale.
• Taylor dispersion experiments were conducted to investigate diffusion on a macroscopic scale.
• A novel protocol was developed to compare mutual diffusion coefficients from both simulation and experimental approaches, accounting for reference frame differences.

Main Results:

• Both molecular simulation and Taylor dispersion experiments yielded results with strong quantitative agreement.
• The study validated experimental ternary mixture results using binary limits of the Fick diffusion matrix and verified Onsager reciprocal relations.
• Maxwell-Stefan diffusion coefficients and thermodynamic factors were consistently sampled by molecular simulation.

Conclusions:

• The developed protocol successfully compared diffusion coefficients from two fundamentally different approaches.
• This coordinated study represents a significant advancement in accurately assessing cross-diffusion in multicomponent mixtures.
• The findings provide a robust understanding of diffusion dynamics in complex aqueous alcohol systems.