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Temperature-Dependent Segregation in Alcohol-Water Binary Mixtures Is Driven by Water Clustering
Samuel Lenton1, Natasha H Rhys1, James J Towey1
1School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , U.K.
The Journal of Physical Chemistry. B
|July 25, 2018
Summary
Aqueous ethanol and methanol solutions show molecular segregation, with water clustering driving the separation of components. This phenomenon is enhanced by cooling and is crucial for understanding excess entropy in these mixtures.
Area of Science:
- Physical Chemistry
- Solution Chemistry
- Materials Science
Background:
- Binary mixtures of methanol and water exhibit partial segregation into water-rich and alcohol-rich phases.
- Both water and methanol form percolating clusters within specific concentration ranges, with segregation intensifying at lower temperatures.
- A mole fraction of 0.27 is significant, coinciding with maximum excess entropy in ethanol-water mixtures.
Purpose of the Study:
- To investigate molecular segregation in aqueous ethanol solutions at a 0.27 mole fraction.
- To compare segregation behavior in ethanol-water with methanol-water mixtures.
- To elucidate the role of water clustering in driving partial segregation and excess entropy.
Main Methods:
- Neutron diffraction was employed to gather structural information.
- Empirical potential structure refinement was used in conjunction with diffraction data.
- Analysis focused on molecular segregation, cluster formation, and inter-molecular interactions.
Main Results:
- Ethanol, similar to methanol, exhibits bi-percolation at a 0.27 mole fraction.
- Cooling enhances alcohol segregation in both ethanol-water and methanol-water solutions.
- Water clustering is significantly amplified in both alcohol solutions compared to non-hydrogen-bonded mixtures.
- Alcohol clustering via hydrophobic groups shows minimal sensitivity to the water hydrogen bond network.
Conclusions:
- Water clustering is the primary driver of partial component segregation in aqueous alcohol solutions.
- The observed segregation and clustering phenomena explain the excess entropy of mixing in these systems.
- Findings support a unified model for segregation in aqueous alcohol mixtures across different alcohol types.
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