Water/oil repellency and drop sliding behavior on carbon nanotubes/carbon paper composite surfaces

The study examines the water/oil repellency and the sliding behavior of carbon papers (CPs) decorated with carbon nanotube (CNT) forest, prepared by using a catalytic chemical vapor deposition. The topography showed that CNTs with 20–40 nm grown on CPs form a hierarchical nano/submicron scale roughness. The CNT–CP composite surface with a thin fluoro-silica coating exhibits excellent water/oil repellency (contact angle >150°) with low sliding angles (SAs), i.e., SA: ∼6° and ∼18° for water and ethylene glycol (EG) droplets, respectively. Taking into account Young–Duprè’s equation incorporated with the Cassie parameter, the work of adhesion (Wad) between droplets and CP surface is significantly reduced because the decoration of CNTs offers an air cushion to repel the drop penetration. The appearance of CNTs contributes area fractions in contact with air, 7.4% and 14.1%, to resist water and EG drops, respectively. The analysis of Wad confirms that the smaller the Wad value, the smaller the SA value reached, thus favoring the self-cleaning effect.