Mechanically Robust, (Super)Hydrophobic Surfaces

In this doctoral study, applied and fundamental research on mechanically robust, (super)hydrophobic surfaces was performed. On the applied front, a simple electro-codeposition process was developed to fabricate non-wetting metal matrix composite coatings with exceptional hardness and resistance to degradation of non-wetting characteristics from abrasive wear compared with a commercial superhydrophobic surface coating. The composites were made of ultra-fine grain / nanocrystalline nickel matrix with embedded hydrophobic particles: polytetrafluoroethylene (PTFE) or rare earth oxide (i.e. cerium oxide) distributed throughout the thickness of the composite coating. Various characterization techniques, including wetting property measurements, electron microscopy, microhardness measurements, and abrasive wear testing were performed to develop the structure – property - performance relationships for this new class of non-wetting material. On the fundamental side, the inherent wettability of rare earth oxides was investigated, as there is currently an active debate in the literature as to whether these ceramics are hydrophobic or hydrophilic. To develop a better understanding on the wettability of rare earth oxides, a study of single crystals with near perfect surfaces was carried out. Epitaxial films of CeO2 and Er2O3 were grown on low Miller index oriented yttria stabilized zirconia single crystal substrates by a pulsed laser deposition technique. Through this study, the crystal orientation – surface energy - wetting property relationships for rare earth oxides were established. Fresh REO epitaxial films were hydrophilic, the water contact angle (WCA) strongly depending on the crystallographic orientation; WCA(111) > WCA(110) > WCA(001), which reflects the differences in surface energy (SN); SN(111)Ph.D