The microscopic structure of cold aqueous methanol mixtures

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Physics

Background:

• Aqueous alcohol mixtures exhibit complex micro-segregated structures.
• Understanding these structures is crucial for predicting mixture properties.
• Previous studies often focused on bulkier water domains in similar mixtures.

Purpose of the Study:

• To investigate the micro-segregation evolution in aqueous methanol mixtures.
• To analyze structural changes from 300 K down to 120 K.
• To elucidate the role of temperature and concentration on cluster formation.

Main Methods:

• Utilized computer simulations for static structural analysis.
• Examined the oxygen-oxygen structure factor to identify heterogeneity.
• Calculated Kirkwood-Buff integrals to assess concentration fluctuations.

Main Results:

• Structural heterogeneity of water increases at lower temperatures, indicated by a pre-peak.
• Water forms predominantly chain-like clusters at lower temperatures and concentrations.
• Methanol domains maintain a chain-like structure at high concentrations, becoming monomeric at lower ones.
• Concentration fluctuations decrease with temperature, leading to quasi-ideal Kirkwood-Buff integrals.

Conclusions:

• Domain segregation in aqueous methanol is driven by linear water clusters.
• This linear water clustering differs from bulkier domains observed in other alcohol-water mixtures.
• The findings offer new insights into the micro-heterogeneous nature of aqueous methanol.