Water friction in nanofluidic channels made from two-dimensional crystals

Area of Science:

• Nanofluidics
• Materials Science
• Physical Chemistry

Background:

• Membrane technologies like desalination and osmotic power generation require efficient water flow in nanoscale channels.
• Understanding and controlling water friction at the solid-liquid interface is crucial for optimizing these applications.
• Current knowledge of mechanisms enabling fast water flows in confined environments remains incomplete.

Purpose of the Study:

• To investigate the influence of confining wall materials on water friction in angstrom-scale capillaries.
• To elucidate the fundamental mechanisms governing water flow and friction at the nanoscale.
• To explore methods for controlling water friction in engineered channels.

Main Methods:

• Fabrication of angstrom-scale capillaries using atomically flat crystalline materials (graphite and hexagonal boron nitride).
• Precision microgravimetry and ion streaming measurements to quantify water friction via slip length.
• Analysis of surface properties including electrical conductivity, wettability, surface charge, and polarity.

Main Results:

• A significant difference in water friction was observed between graphite and hexagonal boron nitride channels, attributed to distinct solid-liquid interactions.
• Slip length, a measure of water friction, was successfully evaluated and correlated with surface properties.
• Demonstrated control over water friction by creating hybrid capillaries with opposing walls exhibiting different slip lengths.

Conclusions:

• The material of confining walls critically influences water friction in nanoscale channels.
• Electrostatic and chemical interactions at the solid-liquid interface are key determinants of water flow.
• This research provides a foundation for designing advanced smart membranes and bio-inspired nanofluidic systems.