Researchers at the National Institute for Interdisciplinary Science and Technology in India have fabricated superhydrophobic nanocomposite coatings composed of carbon nanotubes (CNTs) and oligo(p-phenylenevinylene) (OPV) molecules [Srinivasan, et al., Angew. Chem. Int. Ed. (2008) 47, 5750].
To make the coating, the group suspend CNTs in organic solvents using a variety of OPVs. “OPVs are molecules with π-conjugated backbones which strongly interact with the surface of CNTs through π-πinteraction. The long alkyl chains attached to the OPV molecules wiggle around in the solution and help CNTs to disperse in organic solvents,” explained Ayyappanpillai Ajayaghosh.
The team deposited the CNT/OPV mixtures onto a variety of substrates, then applied water droplets and measured the contact angle (CA). When the contact angle is greater than 150°, the surface is considered superhydrophobic. On the nanocomposite surfaces, the CA was around 165°. “OPVs facilitate the dispersion of CNTs in organic solvents which form coatings on surfaces with water contact angle greater than 160°,” Ajayaghosh said. The CA on a CNT surface was only around 128°. On an OPV surface, the CA was found to be even lower at around 106°.
The researchers have also been able to demonstrate that the surfaces are self-cleaning by using a rolling bead of water to remove a layer of dust. Ajayaghosh explained that the superhydrophobicity originates from roughness in both the micron and nanometer length scales created by the nanotube/OPV nanocomposite, which mimics naturally occurring superhydrophobic surface such as those found on lotus leaves.