High-precision slip length measurement via resistance analysis.

Area of Science:

• Fluid Dynamics
• Surface Science
• Nanotechnology

Background:

• Conventional methods for determining slip length in Newtonian fluids under creeping flow and lubrication approximations suffer from large uncertainties.
• These uncertainties are often attributed to assumed ideal velocity distributions, highlighting the need for alternative approaches.

Purpose of the Study:

• To develop and validate a novel methodology for accurately quantifying slip length without assuming an exact velocity distribution.
• To address the limitations of conventional techniques in measuring slip length under specific fluid flow conditions.

Main Methods:

• Developed a new methodology converting AFM-measured hydrodynamic forces and approach rates into mass flow and velocity-independent resistances.
• Utilized the Stribeck curve to identify appropriate data intervals for analysis.
• Employed high-precision colloidal probe atomic force microscopy (CP-AFM) to study water on silicon surfaces across various velocities.

Main Results:

• The new method yields slip lengths independent of driving velocity.
• The developed approach demonstrates an extended uncertainty less than one-third of conventional methods.
• Quantitatively assessed the contribution of friction resistance (R_Friction) to total resistance (R_Total), revealing its significant decrease with increasing separation.

Conclusions:

• The large uncertainty in conventional slip length measurements arises from underestimating the contribution of friction resistance.
• This work provides a novel and reliable methodology for high-precision slip length determination by decoupling viscous and friction flow components.
• The findings offer a more accurate understanding of fluid behavior at interfaces.