Influence of random roughness on the adhesion between metal surfaces due to capillary condensation

TL;DR

This study investigates how surface roughness affects capillary adhesion between gold surfaces, revealing that increased roughness significantly reduces the capillary force, with implications for nanoscale contact mechanics.

Contribution

It provides experimental insights into the relationship between surface roughness and capillary adhesion, highlighting the transition from smooth to rough contact regimes.

Findings

Capillary force exceeds van der Waals and electrostatic forces on smooth surfaces.

Increasing roughness amplitude from 1 to 10 nm reduces capillary force.

Two regimes identified: smooth limit with macroscopic contact, rough limit with asperity contact.

Abstract

The capillary force was measured by atomic force microscopy between a gold coated sphere mounted on a cantilever and gold surfaces with different roughness. For smooth surfaces the capillary adhesive force surpasses in magnitude any dispersion, e.g. van der Waals/Casimir, and/or electrostatic forces. A substantial decrease in the capillary force was observed by increasing the roughness ampltitude a few nanometers between 1-10 nm. From these measurements two limits can be defined: a smooth limit where a closely macroscopic size contact surface interacts through the capillary force, and the rough limit where only a few asperities give a capillary contribution.