Chemical control of superhydrophobicity of carbon nanotube surfaces: droplet pinning and electrowetting behavior.

We report the remarkable transformation of a superhydrophobic surface of multiwalled carbon nanotubes after chemical manipulation (functionalization, especially by ozonolysis), which leads to a pinning action and eventually hydrophilic behavior, upon the application of an electric field. The effect of droplet pinning on a hydrophobic surface is an indication of the Wenzel formalism, where it is assumed that the liquid fills up the space between the protrusions on the surface. Also, the ozonized bucky surfaces show fascinating electrowetting behavior in the presence of an electrolyte, which follows a transition from a superhydrophobic, Cassie-Baxter state to a hydrophilic, Wenzel state as a function of the electric field, this has been modelled using a simple approach and the corresponding interfacial capacitance has been determined.