Contribution of Capillary Adhesion to Friction at Macroscopic Solid–Solid Interfaces

Capillary adhesion is commonly present in ambient conditions. It can be measured single-asperity contacts through atomic force microscopy using a sharp probe that pulled off smooth substrate. However, for macroscopic multiasperity interfaces, the adhesive always close to zero because of elastic energy stored into deformation surface roughness; this known as paradox. Here, we experimentally show how capillary influences friction between $\mathrm{Si}$-on-$\mathrm{Si}$ covered with native oxide, two vapor environments: humid air and isopropyl alcohol (IPA) vapor. To quantify contribution friction, boundary element method successfully models interplay adhesion, topography, without adjustable parameters evolution topography during sliding dramatically increases thus friction. Replacing water an organic vapor, find lower due smaller tension.