Spraying carbon nanotube dispersions to prepare superhydrophobic films

Carbon nanotubes (CNTs) are a promising material for superhydrophobic coating. In the present study, we prepared superhydrophobic CNT films by spraying CNT dispersions, and discussed the factors that control superhydrophobicity of the CNT films. Three types of dispersions (i.e., CNTs/ethanol, CNTs functionalized with dodecyl groups/ethanol, and CNTs and trimethylsiloxysilicate (TMSS)/ethanol) were prepared as spraying solutions. As increasing the amount of spray-coated CNTs, hydrophobicity of the resulting films became higher, and eventually superhydrophobicity was observed. The spray-coated CNT films had hierarchical roughness, which is preferable morphology to show superhydrophobicity. The coexistence of TMSS in the film lowered the amount of CNTs required to show superhydrophobicity because TMSS acted like glue that prevented CNTs from aggregating on substrates. Interaction force of CNTs also affected the wettability of the CNT films. The pi-pi interaction of CNTs resulted in the aggregation of them on substrates, which lowered the wettability of the films. From this viewpoint, functionalization of CNTs with dodecyl groups was effective to form superhydrophobic films because the dodecyl groups on CNTs screened the pi-pi interaction of CNTs.