Influence of relative humidlty on the pull-off force between spherical tip and plate

Abstract

The pull-off force were measured by using AFM with various curvature radius of a spherical probe in air under the relative humidity controlled. The curvature radii were 8,11,16μm. The tests were performed with four kinds of test specimen (single-crystalline <111> silicon, PTFE, and two super-water-repellent coating film). Pull-off force of silicon increased with increasing relative humidity and curvature radii. On the contrary, the pull-off force of super-water-repellent coating film with large contact angle was independent of relative humidity and curvature radii. From these results, it is found that the influence of the meniscus force by the adsorbed water on the pull-off force is reduced with the super-water-repellent coating film.