Thermodynamic Analysis of n-Hexane-Ethanol Binary Mixtures Using the Kirkwood-Buff Theory

Area of Science:

• Thermodynamics
• Physical Chemistry
• Computational Chemistry

Background:

• Thermodynamic analysis of complex mixtures is challenging.
• Kirkwood-Buff theory estimates properties not directly from simulations, like Gibbs energy of mixing.
• Molecular simulations offer a powerful tool for studying solution behavior.

Purpose of the Study:

• To perform a thermodynamic analysis of n-hexane-ethanol binary mixtures using molecular dynamics simulations.
• To apply Kirkwood-Buff theory to extract thermodynamic properties.
• To investigate the influence of hydrogen bonding on mixing properties.

Main Methods:

• Molecular dynamics simulations in the isothermal-isobaric (NpT) ensemble.
• Calculation of Kirkwood-Buff integrals using Galata's methodology.
• Quantification of composition fluctuations via molecular centers of mass and segments.
• Hydrogen bond identification and analysis.

Main Results:

• Accurate estimation of activity coefficients, excess Gibbs energy, enthalpy, and entropy for n-hexane-ethanol mixtures.
• System size effects on Kirkwood-Buff integral estimation were identified.
• Two methods for composition fluctuation quantification yielded consistent results.
• Simulated results showed excellent agreement with experimental data and prior vapor-liquid equilibria predictions.

Conclusions:

• Molecular dynamics simulations coupled with Kirkwood-Buff theory provide reliable thermodynamic data for complex mixtures.
• Hydrogen bonding significantly impacts the mixing properties of ethanol-containing systems.
• The developed methods are effective for analyzing molecular interactions and thermodynamic behavior in solutions.