Adhesion forces measured by atomic force microscopy in humid air

Area of Science:

• Surface Science
• Materials Science
• Nanotechnology

Background:

• Adhesive forces measured by atomic force microscopy (AFM) are typically attributed to non-surface-specific capillary forces under ambient conditions.
• Understanding the true nature of these forces is crucial for accurate surface characterization and material property assessment.

Purpose of the Study:

• To investigate the nature of atomic force microscopy (AFM) pull-off forces on diverse surfaces.
• To determine the influence of relative humidity on these adhesive forces and identify underlying mechanisms.

Main Methods:

• Utilized atomic force microscopy (AFM) to measure pull-off forces across various surfaces.
• Systematically varied relative humidity to observe its effect on measured adhesive forces.
• Ruled out potential artifacts such as tip-surface contact time and surface roughness.

Main Results:

• Demonstrated chemical specificity in measured pull-off forces, even under conditions favoring capillary condensation.
• Observed a distinct relationship between relative humidity and the magnitude of adhesive forces.
• Confirmed that capillary condensation does not solely dictate the observed pull-off forces.

Conclusions:

• Adhesive forces measured by AFM exhibit chemical specificity, challenging the notion of purely capillary-driven adhesion.
• A mathematical model was developed to explain the observed pull-off force dependence on relative humidity, incorporating chemical specificity.
• This research provides a more nuanced understanding of interfacial forces in AFM measurements.