Understanding Uncertainty and Error in Slip Length Measured by Atomic Force Microscopy (AFM)

Area of Science:

• Fluid mechanics
• Surface science
• Nanotechnology

Background:

• Slip is a crucial boundary condition for fluid behavior at solid-liquid interfaces.
• Atomic force microscopy (AFM), particularly colloidal probe AFM (CP-AFM), is used for slip length measurement but suffers from nanometer-scale errors.

Purpose of the Study:

• Investigate sources of error in AFM-based slip length determination.
• Analyze the impact of factors like curvature, roughness, and velocity on slip length measurements.
• Evaluate error propagation in data processing models.

Main Methods:

• Collected and analyzed existing AFM slip length data from literature.
• Performed quantitative error propagation analysis using Vinogradova models.
• Investigated the effect of data interval selection on slip length determination.

Main Results:

• Curvature, surface roughness, velocity, and data interval choice significantly impact slip length accuracy.
• Both original and simplified Vinogradova models amplify errors during slip-fitting due to error propagation.
• Error amplification in slip-fitting is a primary source of uncertainty in slip length determination.

Conclusions:

• Identified key factors causing discrepancies in slip length measurements using AFM.
• Highlighted error amplification as a major challenge in current slip length determination methods.
• Proposed alternative methods, including a resistance-based approach and the Stribeck interval screening framework, to improve accuracy.