Dynamically and structurally heterogeneous 1-propanol/water mixtures

Area of Science:

• Physical Chemistry
• Materials Science
• Thermodynamics

Background:

• 1-propanol/water mixtures display complex structural and dynamic behaviors.
• Understanding the phase diagram and molecular interactions is crucial for various applications.

Purpose of the Study:

• To construct the phase diagram of 1-propanol/water mixtures across the entire composition range.
• To investigate the structural and dynamic heterogeneity of these mixtures.
• To explore the influence of confinement on water crystallization and dynamics.

Main Methods:

• X-ray diffraction for structural analysis.
• Differential scanning calorimetry for thermodynamic profiling.
• Dielectric spectroscopy for probing molecular dynamics.

Main Results:

• A phase diagram comprising liquid 1-propanol, liquid water, hexagonal ice, and various hydrates was established.
• Four distinct regimes were identified, characterized by droplet arrangements of the minority component.
• Soft confinement of water by 1-propanol prevented crystallization, yielding dynamics akin to high-density liquid (HDL) water.
• Moderate confinement enabled homogeneous nucleation of water at 205 K, within the "no-man's land" region.
• Hydrate formation in 1-propanol-rich mixtures linked to ultra-viscous water phases (HDL and low-density liquid).

Conclusions:

• The study elucidates the intricate phase behavior of 1-propanol/water mixtures.
• Confinement plays a critical role in the crystallization and dynamics of water within these mixtures.
• The findings provide insights into the nature of ultra-viscous water and hydrate formation.