Water Condensation Behavior on the Surface of a Network of Superhydrophobic Carbon Fibers with High-aspect-ratio Nanostructures

Tae-Jun Ko, Eun Kyu Her, Bongsu Shin, Ho-Young Kim, Kwang-Ryeol Lee, Bo Ki Hong, Sae Hoon Kim, Kyu Hwan Oh, Myoung-Woon Moon
 

We have explored the condensation behavior of water on a superhydrophobic carbon fiber (CF) network with high-aspect-ratio hair-like nanostructures. Nanostructures ranging fromnanopillars to hairy shapes were grown on CFs by preferential oxygen plasma etching. Superhydrophobic CF surfaces were achieved by application of a hydrophobic siloxanebased hydrocarbon coating, which increased the water contact angle from 147  to 163 and decreased the contact angle hysteresis from 71  to below 5 , sufficient to cause droplet roll-off from the surface.Water droplet nucleation and growth on the superhydrophobic CF were significantly retarded due to the high-aspect-ratio nanostructures under supersaturated vapor conditions. CFs are observed to wet with condensation between fibers of the pristine surface under super-saturated vapor conditions, which eventually leads to flooding. However, dropwise condensation became dominant in the superhydrophobic CF network, allowing for easy removal of the condensed droplets, which largely allowed the interstitial spaces of the fiber network to remain dry. It is implied that superhydrophobic CF can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell.