We describe a technique to fabricate, for the first time, superoleophobic coatings by spray casting nanoparticle-polymer suspensions. The method involves the use of ZnO nanoparticles blended with a waterborne perfluoroacrylic polymer emulsion using cosolvents. Acetone is shown to be an effective compatibilizing cosolvent to produce self-assembling nanocomposite slurries that form hierarchical nanotextured morphology upon curing. Fabricated coating surface morphology is investigated with an environmental scanning electron microscope (ESEM), and surface wettability is characterized by static and dynamic contact angle measurements. The coatings can be applied to large and/or flexible substrates by spray coating with ease and require no additional surface treatments of commonly used hydrophobic molecules such as fluorosilanes; i.e., the nanocomposites are inherently superoleophobic. The superoleophobic nature of the coatings is also discussed within the framework of Cassie-Baxter and Wenzel wetting theories.

A method to reduce the surface roughness of a spray-casted polyurethane/silica/fluoroacrylic superhydrophobic nanocomposite coating was demonstrated. By changing the main slurry carrier fluid, fluoropolymer medium, surface pretreatment, and spray parameters, we achieved arithmetic surface roughness values of 8.7, 2.7, and 1.6 μm on three test surfaces. The three surfaces displayed superhydrophobic performance with modest variations in skewness and kurtosis. The arithmetic roughness level of 1.6 μm is the smoothest superhydrophobic surface yet produced with these spray-based techniques. These three nanocomposite surfaces, along with a polished aluminum surface, were impacted with a supercooled water spray in icing conditions, and after ice accretion occurred, each was subjected to a pressurized tensile test to measure ice-adhesion. All three superhydrophobic surfaces showed lower ice adhesion than that of the polished aluminum surface. Interestingly, the intermediate roughness surface yielded the best performance, which suggests that high kurtosis and shorter autocorrelation lengths improve performance. The most ice-phobic nanocomposite showed a 60% reduction in ice-adhesion strength when compared to polished aluminum.

Downwind force angles are small for current turbines systems (1–5 MW) such that they may be readily accommodated by conventional upwind configurations. However, analysis indicates that extreme‐scale systems (10–20 MW) will have larger angles that may benefit from downwind‐aligned configurations. To examine potential rotor mass reduction, the pre‐alignment concept was investigated a two‐bladed configuration by keeping the structural and aerodynamic characteristics of each blade fixed (to avoids a complete blade re‐design). Simulations for a 13.2 MW rated rotor at steady‐state conditions show that this concept‐level two‐bladed design may yield 25% rotor mass savings while also reducing average blade stress over all wind speeds. These results employed a pre‐alignment on the basis of a wind speed of 1.25 times the rated wind speed. The downwind pre‐aligned concept may also reduce damage equivalent loads on the blades by 60% for steady rated wind conditions. Even higher mass and damage equivalent load savings (relative to conventional upwind designs) may be possible for larger systems (15–20 MW) for which load‐alignment angles become even larger. However, much more work is needed to determine whether this concept can be translated into a practical design that must meet a wide myriad of other criteria. Copyright © 2017 John Wiley & Sons, Ltd.

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Substrate adhesion was investigated experimentally for superhydrophobic coatings fabricated from polyurethane modified with waterborne perfluoroalkyl methacrylic copolymer and a (fatty amine/amino-silane surface modified) montmorillonite clay nanofiller. The superhydrophobic coatings were obtained by spray casting precursor solutions onto aluminum surfaces. Upon thermosetting, initial static water contact angles exceeding 160 and contact angle hysteresis values below 8 were measured, yielding antiwetting and self-cleaning characteristics. Adhesion strength was then characterized with a 90 tape testing method and was analyzed with respect to changes in surface morphology via electron microscopy as well as changes in wettability. The coating remained adhered to the substrate after repeated adhesion testing with 3850 N/m tape (one of the strongest available), showing higher adhesion than any superhydrophobic coating reported to the author's knowledge. Superhydrophobic performance was also shown to be retained even after repeated tape testing. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: E445-E452, 2012