Contact-pressure-dependent fluid flow regulation at rough interfaces via wetting-modified surface coatings

Understanding fluid flow across rough contact interfaces with tunable wettability is critically important for both fundamental research and industrial applications, particularly in sealing and lubrication. In this work, we modify the wettability of metal sealing gaskets by applying functional coatings fabricated via electrochemical deposition followed by chemical etching and fluor silane grafting. Our experiments reveal a pressure dependent reversal in the effect of wettability on fluid flow. Under high contact pressures, the super-oleophilic coating exhibits a lower flow velocity than its oleophobic counterpart; strikingly, the opposite trend is observed under low contact pressures. The leakage rate of the sealing element can be as low as 0.047 g/min (under conditions of a contact force of 4 tons and a liquid pressure of 6.7 MPa). By integrating fluid pressure, capillary forces, surface roughness, and vortex induced resistance into a modified theoretical framework, we successfully explain the distinct flow behaviors at super-oleophilic and oleophobic contact interfaces. These research results indicate that the properly designed wetting coatings can control the fluid transmission within the microchannels, and the appropriate wetting coatings can be selected based on the range of contact pressure. This work provides a new paradigm for surface engineering in sealing, lubrication, and microfluidic applications.