Fabrication of Transparent Superhydrophobic Surface from ZnO Nanorods.

A transparent superhydrophobic surface was fabricated from ZnO nanorods grown on Si and glass substrates in a thermal furnace for industrial applications such as surface coating. Two types of glasses were used for the substrates: slide glass and Corning glass. The ZnO nanorods were then coated with PTFE using existing sputtering technology and then grown on the glasses. The optical transparency and processing temperature of the nanorods on the substrates with and without a ZnO buffer layer were investigated, for comparison. The superhydrophobic surface formed on Corning glass with a 50-nm-thick ZnO buffer layer exhibited a transparency of 80% or higher and a water contact angle of 150° or higher in the visible light region. High optical transmittance of the superhydrophobic surface was achieved by controlling the size and growth direction of the nanorods. X-ray diffraction and scanning electron microscopy images showed that the nanorods on the glass substrates were thicker than those on Si, and the nanorods predominantly grew in the vertical direction on the buffer layer. However, the growth direction did not affect the wettability of the surface. Vertically grown nanorods can still affect optical transmittance because they facilitate the propagation of light. In the case of Corning glass, superhydrophobic surfaces with contact angles of 150° and 152.3° were formed on both samples with buffer layers of 50 nm and 100 nm, respectively. Therefore, a buffer layer thickness in the range of 50-100 nm is suitable for realizing a transparent superhydrophobic surface on a glass substrate.