When is nanoconfined water different from interfacial water?

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Water behavior differs at surfaces and under confinement.
• The transition point between interfacial and nanoconfinement regimes is unclear.
• Understanding water structure at the nanoscale is crucial for various applications.

Purpose of the Study:

• To investigate the molecular-scale behavior of water confined between graphene surfaces.
• To determine the critical slit width at which water transitions from interfacial to nanoconfinement behavior.
• To elucidate the structural changes in water under angstrom-scale confinement.

Main Methods:

• Machine-learning molecular dynamics simulations with first-principles accuracy.
• Probing water structure across a range of slit widths from open interfaces to angstrom-scale confinement.
• Analyzing density layering, hydrogen bonding, and orientational ordering.

Main Results:

• A sharp structural transition in water was observed.
• Above three water layers, interfacial water structure is similar to open systems.
• Below three layers, angstrom-scale confinement enhances ordering and restructures the hydrogen-bond network.

Conclusions:

• Established a clear molecular-level distinction between interfacial water and nanoconfined water.
• Identified a critical threshold for water structural transition based on layer thickness.
• Provides insights for controlling water structure in nanoscale solid-liquid systems.