Superhydrophobic Micro/Nano Dual-Scale Structures

In this paper, we present superhydrophobic micro/nano dual structures (MNDS). By KOH-etching of silicon, well-designed microstructures, including inverted pyramids and V-shape grooves, are first fabricated with certain geometry sizes. Nanostructures made of high-compact high-aspect-ratio nanopillars are then formed atop microstructures by an improved controllable deep reactive ion etching (DRIE) process without masks, thus forming MNDS. Resulting from both the minimized liquid solid contact area and the fluorocarbon layer atop deposited during the DRIE process, the MNDS show a reliable superhydrophobicity. The contact angle and contact angle hysteresis are similar to 165 and less than 1 degrees, respectively. This superhydrophobicity of MNDS is very stable according to squeezing and dropping test, even in high voltage conditions with the electrowetting threshold voltage of similar to 300 V. Therefore, this micro/nano dual-scale structure has strong potential applications to the self-cleaning surface and superhydrophobic micro/nano fluidics.