Superlubricity: a paradox about confined fluids resolved

Area of Science:

• Surface Science
• Tribology
• Fluid Dynamics

Background:

• Molecular dynamics (MD) simulations predicted specific behaviors of alkane fluids at solid-fluid interfaces.
• Prior experimental results showed discrepancies with these MD predictions, creating a paradox in understanding fluid behavior.

Purpose of the Study:

• To investigate alkane fluids using a surface forces apparatus.
• To reconcile experimental findings with molecular dynamics simulation predictions.
• To explore energy dissipation mechanisms at smooth solid-fluid interfaces.

Main Methods:

• Utilized the Frantz and Salmeron method to cleave mica surfaces.
• Employed a surface forces apparatus to study alkane fluids, including squalane.
• Inferred boundary slip from frictional sliding of thin films and hydrodynamic flow of thicker films.

Main Results:

• Observed an oscillatory force-distance profile for the methyl-branched alkane, squalane.
• Confirmed boundary slip in molecularly thin fluids and thicker films.
• Demonstrated exceptionally low energy dissipation for fluids moving past smooth surfaces.

Conclusions:

• Experimental results now align with molecular dynamics simulation predictions for alkane fluids.
• Boundary slip is a key phenomenon in fluid behavior at interfaces.
• Smooth surfaces enable significantly reduced energy dissipation during fluid flow.