Low- and High-Density Unknown Waters at Ice-Water Interfaces.

Area of Science:

• Physical Chemistry
• Materials Science
• Thermodynamics

Background:

• Understanding water's liquid states, including high-density liquid (HDL) and low-density liquid (LDL) polymorphs, is crucial for explaining its unique properties.
• Experimental verification of liquid water polymorphs is hindered by the liquid-liquid critical point residing in the inaccessible "no man's land" region of supercooled conditions.

Purpose of the Study:

• To experimentally confirm the existence of distinct liquid polymorphs of water under accessible conditions.
• To investigate the formation and characteristics of these liquid water phases at interfaces with ice.

Main Methods:

• Utilized in situ optical microscopy to observe water-ice interfaces.
• Investigated non-equilibrium interfaces between water and various ice polymorphs under accessible depressurization conditions.
• Measured characteristic velocities of observed water phases.

Main Results:

• Observed macroscopic droplets and layers of low-density unknown water (LDUW) and high-density unknown water (HDUW) dependent on ice polymorphs.
• These unknown water phases appeared at non-equilibrium interfaces under experimentally accessible conditions.
• Measured distinct characteristic velocities for LDUW (approx. 20 m/s), HDUW (approx. 100 m/s), bulk water (approx. 40 m/s), and quasi-liquid layers (QLLs) (approx. 2 m/s and 0.2 m/s).

Conclusions:

• The study provides experimental evidence for the existence of distinct liquid polymorphs of water (LDUW and HDUW).
• These findings offer insights into the long-sought liquid polymorphism of water and its behavior at interfaces.