Reversible Superhydrophobic to Superhydrophilic Conversion of Ag@TiO2 Composite Nanofiber Surfaces

A new type of superhydrophobic material consisting of a surface with supported Ag@TiO₂ core−shell nanofibers has been prepared at low temperature by plasma-enhanced chemical vapor deposition (PECVD). The fibers are formed by an inner nanocrystalline silver thread which is covered by a TiO₂ overlayer. Water contact angles depend on the width of the fibers and on their surface concentration, reaching a maximum wetting angle close to 180° for a surface concentration of 15 fibers µm⁻² and a thickness of 200 nm. When irradiated with UV light, these surfaces become superhydrophilic (i.e., 0° contact angle). The decrease rate of the contact angle depends on both the crystalline state of the titania and on the size of the individual TiO₂ domains covering the fibers. To the best of our knowledge, this is one of the few examples existing in the literature where a superhydrophobic surface transforms reversibly into a superhydrophilic one as an effect of light irradiation.