Wetting and anti-wetting on aligned carbon nanotube films

This review covers recent advances in the wettability of aligned carbon nanotubes (ACNT). Carbon nanotubes (CNT) are inherently somewhat hydrophilic, with a water contact angle of less than 86 degrees. When they are arranged in a textured manner on substrates having different surface topographies, different wettabilities are exhibited. These range from hydrophilic to hydrophobic, and even superhydrophobic, and with isotropic to anisotropic contact angle (CA) hysteresis. If chemical modification is involved, the wettability can be adjusted from superhydrophobic to superhydrophilic on a certain structured ACNTs. Here, we first examine the structural influence of isotropic roughness on this effect (including nano-structures and hierarchical structures), where isotropic wetting (including wetting and anti-wetting) is observed. Water can wet the nanostructured CNT alignment, resulting in self-assembly; on the other hand, superhydrophobicity is durable on hierarchical and chemically-modified nano-structured alignments. Secondly, the effects of anisotropic roughness on wetting behavior are discussed. Finally, we suggest the remaining challenges in the field, and several practical applications of ACNT possessing special wettability.