Particle adhesion on highly rough hydrophobic surfaces: The distribution of interaction mechanisms

Capillary forces caused by nano-bubbles at the surface have a considerable influence on the adhesive forces acting on hydrophobic surfaces. The existence of these bubbles is proved on smooth surfaces after preparation processes like solvent exchange or temperature change, which leads to supersaturated liquids and the formation of nano-bubbles on the surface. On highly rough surfaces, the typical procedures like topography scans to evaluate the existence of nano-bubbles are not possible. The approach taken in this study is the validation of nano-bubbles on rough surfaces by force/distance measurements using contact-mode atomic force microscopy. Afterwards, the obtained data is analyzed and subdivided into classes of interaction mechanisms, which represent either capillary forces or non-capillary forces. With this strategy, nano-bubbles can be identified that occur after the addition of the liquid to rough surfaces. The results indicate relations between the frequency and snap-in distance and the measured macroscopic wetting angle. This correlation allows an estimation of the probability of occurrence of capillary and non-capillary forces.