The impact of water drops on a grooved surface exhibiting hydrophobic features is studied experimentally. The grooved surface is made of stainless steel and is comprised of a structure of unidirectional grooves. The groove structure yielded contact angles 135° and 107° for water on the surface perpendicular to the groove direction and parallel to the groove direction respectively compared to 80° on a smooth stainless steel surface. The influence of groove structure on the drop impact process is studied by comparing the experimental results of drop impact on the grooved surface with those obtained for the smooth surface. The groove structure alters the shape of the liquid lamella spreading on the grooved surface. For the impact of high inertia drops on the grooved surface, the droplet liquid flowing inside the grooves ejects out as tiny droplets during early stages of the impact. On the grooved surface, the impacting drop spreads along the groove direction in a similar manner as observed on the smooth surface, and the solid pillars of the grooved surface hinder the spreading of droplet liquid perpendicular to the groove direction. The enhanced hydrophobicity of the grooved surface makes the droplet liquid to rebound more intensely than that on the smooth surface.
Dr. R. Kannan and Sivakumar, D., “Drop Impact Process on a Hydrophobic Grooved Surface”, Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 317, pp. 694 - 704, 2008.