Exploring Defect Height and Angle on Asymmetric Contact Line Pinning

Wetting of structured surfaces is of great interest but is mainly studied for Cassie state wetting. To avoid trapping of air, surfaces structured with pyramid-shaped defects are manufactured rather than pillars. Wenzel state advancing and receding water contact angles are measured on these tailored rough surfaces. Asymmetric results are found for sessile drop and captive bubble configurations. These discrepancies are attributed to the contact line curvature and different pinning forces, which appear along the contact line, reflecting the geometry. An estimate for the effect of the surface topography on advancing and receding contact angles in both configurations is derived and compared with the experimental data.