Active gas replenishment for super-hydrophobic surface by porous material and gas injection

Super-Hydrophobic Surface (SHS) has a wide range of engineering applications, from reducing drag, to enhancing heat and mass transfer, protecting solid surface against icing, corrosion, and bio-fouling. However, most of these benefits can be destroyed when the gas (or plastron) trapped on the SHS is replaced by the liquid, a process known as wetting transition. Here, we developed and tested an active gas replenishment technology based on creating SHS on a porous base and injecting gas through the porous material. A series of SHSs were fabricated by spraying Ultra-Ever-Dry coating (a commercial superhydrophobic coating) on porous stainless steel. The porous bases have a pore size ranging from 2 to 20 μm. For comparison, non-porous SHSs were also fabricated by the same procedure. The fabricated SHSs was experimentally tests in both stationary liquid and turbulent channel flows. The pressure difference across the porous SHS was precisely controlled by pressure regulators. The gas layer on SHS was evaluated by total- internal-reflection. We found that the porous SHSs sustained dry when subjected to high pressure, gas dissolution, and turbulent flows, while the non-porous SHSs underwent a wetting transition at same experimental conditions.