Superhydrophobic surfaces with a dual-layer micro- and nanoparticle coating for drag reduction

We propose a facile and cost effective method for fabricating superhydrophobic surfaces with significant drag reduction in a wide velocity range. A dual structure superhydrophobic aluminum surface with a hydrophobic Al2O3 micro- and nanoparticle coating and also another superhydrophobic surface with a nanoparticle layer coating are fabricated. Then, the resulted drag from each of these surfaces is measured carefully in different velocities and compared with the drag of the as-received aluminum surface. Our results reveal that the surface with the dual structure experiences drag reduction in a wider velocity range compared with the nanoparticle coated sample. Drag reduction of the dual structure substrate is between 77 and 5% for Reynolds number of 4.7 × 104 and 2.35 × 105, respectively. The fabricated dual structure also shows a good durability which makes it favorable for many applications.