Widom Lines in Binary Mixtures of Supercritical Fluids.

Area of Science:

• Thermodynamics
• Physical Chemistry
• Fluid Dynamics

Background:

• Supercritical fluids exhibit distinct liquid-like and gas-like behaviors.
• The Widom line marks supercritical liquid-gas transitions in pure fluids.
• Supercritical transitions in mixtures remain poorly understood.

Purpose of the Study:

• Investigate supercritical state transitions in binary mixtures.
• Determine if Widom lines exist in binary mixtures.
• Characterize pathways of liquid-gas transitions in mixtures.

Main Methods:

• Molecular dynamics simulations of noble gas mixtures.
• Analysis of response functions to identify transition lines.
• Comparison of miscible and immiscible binary mixture behaviors.

Main Results:

• First evidence for multiple Widom lines in binary mixtures.
• Miscible mixtures show a single Widom line, analogous to pure fluids.
• Immiscible mixtures exhibit phase separation with multiple Widom lines.

Conclusions:

• Supercritical transitions in binary mixtures are complex and varied.
• Phase behavior dictates the number and nature of Widom lines.
• Findings highlight the complexity of supercritical states in multi-component mixtures.