In Situ Determination of the Water Condensation Mechanisms on Superhydrophobic and Superhydrophilic Titanium Dioxide Nanotubes

Abstract

One-dimensional (1D) nanostructured surfaces based on high-density arrays of nanowires and nanotubes of photoactive titanium dioxide (TiO) present a tunable wetting behavior from superhydrophobic to superhydrophilic states. These situations are depicted in a reversible way by simply irradiating with ultraviolet light (superhydrophobic to superhydrophilic) and storage in dark. In this article, we combine in situ environmental scanning electron microscopy (ESEM) and near ambient pressure photoemission analysis (NAPP) to understand this transition. These experiments reveal complementary information at microscopic and atomic level reflecting the surface wettability and chemical state modifications experienced by these 1D surfaces upon irradiation. We pay special attention to the role of the water condensation mechanisms and try to elucidate the relationship between apparent water contact angles of sessile drops under ambient conditions at the macroscale with the formation of droplets by water condensation at low temperature and increasing humidity on the nanotubes' surfaces. Thus, for the as-grown nanotubes, we reveal a metastable and superhydrophobic Cassie state for sessile drops that tunes toward water dropwise condensation at the microscale compatible with a partial hydrophobic Wenzel state. For the UV-irradiated surfaces, a filmwise wetting behavior is observed for both condensed water and sessile droplets. NAPP analyses show a hydroxyl accumulation on the as-grown nanotubes surfaces during the exposure to water condensation conditions, whereas the water filmwise condensation on a previously hydroxyl enriched surface is proved for the superhydrophilic counterpart.

3D core-multishell piezoelectric nanogenerators

“…[20][21] In recent articles, we have successfully applied such approach for the alignment of magnetic molecular wires, [18] formation of nanoscale waveguides, [19] development of 1D and 3D photoanodes for dyesensitized solar cells [24] and the fabrication of tuneable superhydrophobic-superhydrophilic surfaces. [25] In this communication, we aim to do a loop forward towards the exploitation of the advantages of the method by demonstrating its successful application to develop highly integrated energy harvesting devices.…”

Influence of Titanium Oxide Pillar Array Nanometric Structures and Ultraviolet Irradiation on the Properties of the Surface of Dental Implants—A Pilot Study

“…Together with the main peak, a shoulder appears at 288.6 eV, which corresponds to the species –CCO–. Furthermore, in the untreated grade V sample, a signal can be seen between 280 and 285.5 eV, which could correspond to the species TiC [47].…”

Plasma‐Assisted Deposition of TiO2 3D Nanomembranes: Selective Wetting, Superomniphobicity, and Self‐Cleaning

“…Here, we will profit from the photoactive response of the TiO 2 shells to allow the reversible superhydrophobic-to-superhydrophilic conversion upon illumination with UV light. [25,26] The graphs in Figure 5 present the evolution of the 3D nanomembrane's contact angle to water under a) visible (Vis) and b) UV-vis illumination. Interestingly, the water contact angle of the surfaces fabricated on cellulose and metallic grids is decreased after the first minutes of illumination with Vis light, and an unexpected result as the TiO 2 presents photoactivity under excitation at UV wavelengths.…”

“…Other hydrophobic membranes decorated with TiO 2 nanoparticles have revealed slower photoactivation [29] or needed high synthesis temperature protocols. [30] Mechanisms of water condensation onto hydrophilic or hydrophobic TiO 2 thin films and highly porous nanostructures have been previously studied [26,31,32] to control precisely the photoactivation of wettability. As also reported for other photoactive, low-dimensional metal oxide nanomaterials, the superhydrophobic character of the surfaces can be recovered by heating, dark storage during a few weeks, or in a low vacuum overnight.…”