The effect of the surface wettability of nanoprotrusions formed on network-type microstructures

Hexagonal network-type silicon microstructures with nanoprotrusions were designed, fabricated, and their surface wettability was characterized. The nanoprotrusions were fabricated by reactive ion etching (RIE). The microstructures were fabricated by deep reactive ion etching (DRIE). For hydrophobicity, plasma polymerized fluorocarbon (PPFC) of a hydrophobic nature was coated onto the surface of the microstructures with nanoprotrusions. Through a comparison of the contact angles between hexagonal network-type microstructures with nanoprotrusions and those without nanoprotrusions, the effect of the nanoprotrusions on the surface wettability was evaluated. The average value of the contact angles measured from microstructures with nanoprotrusions was 18. higher than that measured from microstructures without nanoprotrusions. Nanoprotrusions decrease the contact area between a water droplet and the surface, causing the contact angles to increase considerably. The wetting mode of the nano- and micro-multiscale structured surface changed with the pore ratio of the microstructures. While the water was fully supported by the nanoprotrusions at a low pore ratio, the water fully wetted the nanoprotrusions at a high pore ratio.