Viscosity of interfacial water.

Area of Science:

• Physical Chemistry
• Surface Science
• Materials Science

Background:

• Understanding the behavior of confined water is crucial for various scientific fields.
• Previous studies have proposed specific structures, like
• ice structures
• for ultrathin water layers.

Purpose of the Study:

• To investigate the effective shear viscosity and dynamic oscillatory shear spectra of confined ionic water.
• To explore the influence of confinement and ionic strength on water's rheological properties.
• To dynamically probe the structure of ultrathin water films.

Main Methods:

• Confining water with monovalent or divalent ions (25 mM ionic strength) between mica crystals to a thickness of 1-2 molecular layers.
• Measuring effective shear viscosity and frequency-dependent dynamic oscillatory shear spectra.
• Analyzing the oscillation of these properties with varying twist angles between the mica crystals.

Main Results:

• Effective shear viscosity and shear spectra oscillated with the twist angle, matching the pseudohexagonal surface lattice period.
• Viscosity varied by orders of magnitude with changes in twist angle.
• Confinement induced lateral spatial correlations in the water layer, enhanced by lattice alignment, but no dynamic "ice structure" was observed.

Conclusions:

• The rheology of confined ionic water is highly sensitive to the surface lattice structure and alignment.
• Confinement significantly impacts the lateral organization of water molecules.
• Dynamic experimental evidence for the proposed
• ice structure
• in such confined water films was not found.