Large slip of aqueous liquid flow over a nanoengineered superhydrophobic surface

While many recent studies have confirmed the existence of liquid slip over certain solid surfaces, there has not been a deliberate effort to design and fabricate a surface that would maximize the slip under practical conditions. Here, we have engineered a nanostructured superhydrophobic surface that minimizes the liquid-solid contact area so that the liquid flows predominantly over a layer of air. Measured through a cone-and-plate rheometer system, the surface has demonstrated dramatic slip effects: a slip length of ∼20 μm for water flow and ∼50 μm for 30 glycerin. The essential geometrical characteristics lie with the nanoposts populated on the surface: tall and slender (i.e., needlelike) profile and submicron periodicity (i.e., pitch).