Reversible Electrowetting of Vertically Aligned Superhydrophobic Carbon Nanofibers

Reversible electrostatically induced wetting (electrowetting) of vertically aligned superhydrophobic carbon nanofibers has been investigated. Carbon nanofibers on a 5 × 5 μm pitch were grown on Si substrates, electrically insulated with a conformal dielectric, and hydrophobized with fluoropolymer. This nanostructured scaffold exhibited superhydrophobic behavior for saline (θ ≈ 160°). Electrowetting induced a contact angle reduction to θ ≈ 100°. Competitive two-liquid (dodecane/saline) electrowetting exhibited reversibility on the same nanostructured scaffold. Without applied bias, ultra-fine-point tip (∼25 nm radius) nanofibers result in effectively zero capacitance with the overlying saline layer. Complete electrowetting of the substrate is confirmed as capacitance values increase by several orders of magnitude with increased wetting. These results demonstrate the applicability of reversible electrowetting on nanostructured scaffolds and use of nanofabricated structures that can be integrated with various micro- and nanoelectronic technologies.