Controllable Wettability And Morphology Of Electrodeposited Surfaces On Zinc Substrates

Surface wettability is a property of great importance in determining the application of solid materials, which is closely governed by surface chemistry and topographical microstructure. The surfaces with reversibly switchable wettability between superhydrophobicity(with water contact angle(CA) larger than 150°) and superhydrophilicity(with water CA less than 5°) have aroused tremendous interest due to their various unique applications in self-cleaning, biomaterials, sensor devices, ink-jet printing, intelligent microfluidic, controllable drug delivery and lab-on-chip systems, etc. Zn O is a promising candidate in building functional electronic devices depending on its distinctive physical and chemical properties. Their properties and performance would be varied according to the adjustment of the shape, size, orientation, and density of Zn O. Thus, development of controllable synthesis of Zn O materials in morphology is urgently necessary for exploring the extension of Zn O. The intelligent switchable surfaces with controllable wettability and morphology offer possibilities for chemical, biological, electronic and microfluidic applications. The major studies and innovative results are as follows:(1) Superhydrophobic surfaces combining hierarchical micro/nanostructures were fabricated on zinc substrates by etching in hydrochloric acid solution, electrodeposition of Zn O coatings and subsequent thermal annealing. The optimal coatings were electrodeopsited at-1.25 V for 900 s on the etched zinc substrates and then annealed at 200 °C for 60 min, which could achieve a maximum water contact angle of 170 ± 2° and an ultra-low sliding angle of approximately 0°. By conducting SEM and water CA analysis, we found that the morphology and wettability of prepared samples were controllable by the fabrication process. Interestingly, even without any additional modification, the samples prepared under different electrodeposition conditions(including Zn(CH3COO)2 concentration from 5 m M to 40 m M and deposition time from 300 s to 1500 s) exhibited superhydrophobic character. The influences of the etching time, Zn(CH3COO)2 concentration, deposition time, annealing temperature and annealing time on the wetting behaviors were also discussed in detail.(2) The surface wettability, chemical composition and morphology were investigated by contact angle measurements(CA), Powder X-ray diffraction analysis(XRD), X-ray photoelectron spectroscopy(XPS) and scanning electron microscope(SEM). The theoretical growth mechanism and principles of the superhydrophobic surfaces were investigated in detail.(3) The stability experiment and electrochemical corrosion measurements were carried out for the superhydrophobic surfaces. The experimental results showed that such superhydrophobic surfaces possess long-term stability, and good corrosion resistance as well as self-cleaning ability. In addition, the anti-icing properties of the Zn O films were investigated. These surfaces could be rapidly and reversibly switched between superhydrophobicity and superhydrophilicity by alternating UV illumination and dark storage or thermal annealing.