Interplay between capillary and dispersion forces in adhesion under ambient conditions

Area of Science:

• Surface Science
• Tribology
• Nanotechnology

Background:

• Conflicting adhesion force measurements for hydrophilic rough surfaces below critical humidity exist.
• Previous studies attributed discrepancies to roughness or capillary interactions, but lacked a unified explanation.

Purpose of the Study:

• To resolve the controversy surrounding adhesion forces on rough surfaces at controlled humidity.
• To provide a unified model explaining discrepancies between adhered cantilever and atomic force microscope (AFM) measurements.

Main Methods:

• Utilized detailed atomic force microscope (AFM) scans to extract surface information without assuming roughness.
• Applied a force balance equation incorporating long-distance dispersion forces and nominal contact area.
• Determined adhesion force, its variation, and average contact distance from experimental data.

Main Results:

• Demonstrated that for larger roughness, capillary and short-distance forces increase slower with area, enhancing the role of dispersion forces.
• Showed that varying nominal contact areas in adhered cantilever versus AFM experiments explain the observed contradictions.
• Identified average contact distance as a critical factor influencing the relative contributions of different adhesion forces.

Conclusions:

• The study reconciles conflicting adhesion force measurements by considering surface roughness, contact area, and multiple force contributions.
• A comprehensive force balance model accurately predicts adhesion forces and variations on rough surfaces.
• Experimental conditions, particularly the nominal contact area, are crucial for interpreting adhesion measurements.