Stable hierarchical superhydrophobic surfaces based on vertically aligned carbon nanotube forests modified with conformal silicone coating

Unique and inherent nano-roughened morphologies of vertically aligned carbon nanotube (VACNT) forests are desirable for mimicking biological superhydrophobic surface systems. In this paper, we report on a new class of robust dual-roughened superhydrophobic surfaces based on VACNT forests coated conformally with thin silicone. The vapor phase deposition of silicone considerably reduces the surface energy of the VACNTs by conformally and completely covering the vertical structures. This significantly enhances the superhydrophobic robustness of the VACNTs by preventing the surfaces from being wet, even under pressurized conditions. In addition, micro-patterning based on a simple contact transfer technique enables easy fabrication of VACNT micro-pillar arrays with various pillar-to-pillar spacings ranging from 45 to 160 μm with respect to a fixed width of ∼65 μm. A combination of simple contact transfer and subsequent silicone coating techniques facilitates the achievement of micro/nano hierarchical VACNT superhydrophobic surfaces with superior wetting properties (high water contact angle of 168 ± 0.3°, low contact angle hysteresis of 2.64 ± 0.4°, and low sliding angle of <∼5°) and water-repellent performance (even at impact velocity of up to ∼1.4 m/s) while ensuring superhydrophobic robustness.