Obtaining superhydrophobicity using commercial razor blades

Because the superhydrophobic characteristic appears by forming a composite surface consisting of solid and air underneath the droplets, a large number of rough surfaces that can trap air have been fabricated. Recently, the air trapping on materials whose equilibrium contact angles are less than 90 degrees was achieved by fabricating proper structures that lead energetic stability at the condition. Whereas these methods were proposed under the assumption of the static and equilibrium conditions, we take a dynamic and non-equilibrium approach in this study through droplet deposition and droplet impact experiments. By employing test surfaces that consist of commercially available stainless steel razor blades, we show the pinning effect brings the apparent water contact angle of approximately 160 degrees on a "hydrophilic" substrate. We call this state the "non-equilibrium Cassie state" and give theoretical explanations. Furthermore, the dynamic characteristics of the droplet impact on these surfaces are discussed in a range of moderate Weber numbers.