Measuring forces with the AFM: polymeric surfaces in liquids

Area of Science:

• Surface science
• Materials science
• Biophysics

Background:

• Atomic Force Microscopy (AFM) is a key technique for probing forces at the nanoscale.
• Understanding intersurface forces is crucial for applications in materials science and biology.
• Previous studies have investigated forces between various surfaces, but a consolidated view of practical measurement challenges is lacking.

Purpose of the Study:

• To review the practical aspects of force measurement using AFM between polymeric, surfactant, and biologically coated surfaces in liquids.
• To compare AFM force measurements with those obtained from Surface Force Apparatus (SFA).
• To analyze the similarities and irregularities in measured forces and discuss their origins.

Main Methods:

• Literature review of studies employing AFM for force measurements between different types of surfaces in liquid environments.
• Comparative analysis of AFM data with existing Surface Force Apparatus (SFA) data.
• Discussion of practical considerations and challenges in performing and interpreting force measurements.

Main Results:

• Forces between surfaces in liquids are a complex combination of steric repulsion and conformational changes.
• Long-range attractive forces, often termed 'hydrophobic' forces, are frequently observed but their origin remains uncertain.
• AFM measurements reveal similarities and irregularities when compared to SFA, highlighting the importance of experimental context.

Conclusions:

• AFM is a versatile tool for studying intersurface forces, but practical challenges in measurement and interpretation persist.
• The 'hydrophobic' force remains a significant area for further investigation due to its prevalence and unclear origin.
• A comprehensive understanding of these forces requires integrating data from various techniques like AFM and SFA.