Water Droplet Adhesion on Hydrophobic Surfaces: Influence of Droplet Size and Inclination Angle of Surface on Adhesion Force

Abstract

Adhesion of various size sessile droplets on the hydrophobic surfaces is considered, and the moment generated about the locus of the droplet meniscus is determined for several inclination angles of hydrophobic surface. An experiment is designed to examine the influence of inclination of hydrophobic surface on the water droplet behavior. The flow field generated inside the droplet is simulated to predict the flow acceleration and its effects on adhesion force. Simulations are repeated for different inclination angles of hydrophobic surface. The flow predictions are validated through the experimental data. It is found that the moment about the locus of droplet meniscus increases with increasing inclination angle, which is more pronounced for the large volume water droplets, such as ∀ = 45 μL; however, further increase of inclination angle lowers the moment because of significant change of the location of the line of action of the total force during the excessive body deformation of the droplet. The flow field developed inside the droplet forms a circulation cell, and the orientation and size of the circulation cell change with droplet volume, which becomes significant at high inclination angles. The flow acceleration inside the droplet does not have significant contribution to the overall force generated on the droplet during the inclination of the hydrophobic surface. The shear force generated at the wetted surface of the droplet plays in significant role on the adhesion force.