Transforming an intrinsically hydrophilic polymer to a robust self-cleaning superhydrophobic coating via carbon nanotube surface embedding

Highlights: • An intrinsically hydrophilic polymer was transformed to a superhydrophobic material. • Surface roughness plays a more important role in designing superhydrophobic materials. • At longer processing times, superhydrophobicity is reduced due to penetration of polymer chains into the CNTs' pores. - Abstract: A single-step method, including surface embedding of nanoparticles into a polymer matrix, was employed to fabricate superhydrophobic thermoplastic polyurethane (TPU)/carbon nanotube (CNT) nanocomposite coatings. The main aim was to prove that surface roughness plays a more important role in designing superhydrophobic surfaces as compared with the surface energy. Therefore, TPU was used as the model hydrophilic polymer and CNTs were employed as non-hydrophobic nanoparticles. It was found that, at a certain pressing time, CNTs form an efficient hair-like morphology which is able to highly enclose air within its as-formed pores leading to superhydrophobic behavior. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal microscopy were utilized for characterization of samples. SEM and confocal microscopy results proved that surface roughness played the key role in the final wettability behavior. Based on XPS results, it was also found that a very long pressing time led to partial migration of TPU macromolecules into the CNTs' pores, and hence, superhydrophobicity was reduced. The effects of mechanical abrasion and nanoparticle type on wettability behavior of samples were evaluated as well. In conclusion, it is suggested that surface roughness factor should be highly considered in designing superhydrophobic nanocomposite coatings rather than surface energy.