Capillary force between wetted nanometric contacts and its application to atomic force microscopy.

Area of Science:

• Fluid dynamics
• Surface science
• Nanotechnology

Background:

• Understanding capillary forces is crucial for micro/nanoscale adhesion.
• Previous models for pendular rings were limited, especially for perfect wetting scenarios.
• Accurate force calculations are needed for nanoparticle interactions and AFM measurements.

Purpose of the Study:

• To extend existing calculations of capillary forces for pendular rings to the case of perfect wetting.
• To derive and validate an approximate analytical expression for capillary forces between highly curved, liquid-film-covered surfaces.
• To provide a quantitative tool for estimating adhesion forces in wet nanoparticle systems.

Main Methods:

• Extending the exact calculation method of Orr et al. for pendular rings.
• Deriving an approximate analytical expression for capillary forces.
• Utilizing custom-made numerical simulations based on the full exact mathematical description to assess and extend the analytical model's validity.

Main Results:

• An approximate analytical expression for capillary force in perfect wetting was derived.
• Numerical simulations validated and extended the domain of validity for the analytical expression.
• The capillary force was found to increase monotonically with decreasing vapor pressure for attractive van der Waals interactions.

Conclusions:

• The derived analytical expression accurately describes capillary forces for wet nanoparticles under perfect wetting.
• This work enables better estimation of adhesion forces between wet nanoparticles.
• The findings offer a quantitative method for interpreting pull-off forces in atomic force microscopy experiments.