Slip length measurement of pdms/hydrophobic silica superhydrophobic coating for drag reduction application

This paper aims to study the drag reduction of a superhydrophobic nanocomposite coating for engineering applications. In the method developed, a suspension of hydrophobic silica nanoparticles in PDMS/toluene solution was prepared. Then a spray-deposition method is used to deposit a layer of nanocomposite composed of PDMS/hydrophobic silica nanoparticles on the surface. After curing the samples at 100 °C for 1 h the nanocomposite coating was prepared. The surface morphology of the coating was characterized by scanning electron microscopy and static water contact angle measurement. The superhydrophobic properties of fabricated surfaces are investigated through different PDMS/hydrophobic silica nanoparticles ratios. It was found that the presented nanocomposite coating method was an effective technology which was suitable to form large-area superhydrophobic coating with a water droplet (5 μL) roll-off angle of less than 5°. The hydrostatic pressure test showed that the Cassie−Baxter state of the fabricated coating is stable in front of the applied pressure up to 50 kPa. Drag reduction tests showed that the air-layer placed at the water-superhydrophobic interface was stable in front of wall shear stress up to 11 Pa. The maximum drag reduction and slip length were measured about 25% and 70 μm, respectively.