# Superhydrophobic Coating Solutions for Deicing Control in Aircraft
## 3 Superhydrophobic Surface with Icephobic Behaviour for Aircraft Applications
### SHS Tested in Flight Conditions
This material was obtained on stainless steel by depositing first TiO\({}_{2}\) powder by suspension plasma spray and secondly, a thin coating of diamond-like carbon network with SiO\({}_{2}\) by plasma enhanced chemical vapor deposition. The prepared coating showed CA = 159\({}^{\circ}\), CAH = 3.8\({}^{\circ}\) and Sa = 10.3 \(\upmu\)m. The SH coating was exposed to icing/deicing cycling (IWT), rain erosion, and accelerate/adaping test, and the results were compared with those from tests performed on SH TiO\({}_{2}\)/stearic acid and commercial hydrophobic fluoropolymer. The IWT test conditions were T = \(-10\)\({}^{\circ}\)C with air speed of 43 m/s and LWC of 0.5 g/m\({}^{3}\). At the end of the study, it was possible to affirm that the prepared SH coating was resistant to UV exposure, and could resist up to 6000 water droplets impact at 165 m/s and especially started to degrade after 170 icing/deicing cycles resulting in the coating with the best performance. However, the authors pointed out that, although the test in IVT was under severe conditions, deicing by melting and removal of ice through this method was less damaging than removing it by shearing force and that, if this situation could arise, the coating would degrade much faster. As above noted, the works just reported all apply specific test conditions that are very close to real ones even if they are often different from each other. In general, it is observed that SHS decreases the energy required to melt ice in AIPS and that the greater or lesser effectiveness depends on the type of formed ice. Until now, we revised articles where wettability studies did not take into account the reported roughness values. In the following papers, however, this relationship has been carefully analyzed to draw more accurate conclusions after IWT testing. [PERSON] et al. [36] investigated by IWT tests hydrophobic and superhydrophobic surfaces created on an aluminum alloy commonly used for aerospace components. The different wettability and roughness were obtained working on the Al alloy anodization in different media, sulphuric (SA) or oxalic acid (OA), and subsequently, each sample was functionalized by spraying a commercial hydrophobizing agent. OA samples were hydrophobic (max CA = 146\({}^{\circ}\), RoA = 81\({}^{\circ}\)) with max surface roughness of 0.32 \(\upmu\)m, SA samples were superhydrophobic with CA of 162\({}^{\circ}\) and 170\({}^{\circ}\), RoA of 32 and 4\({}^{\circ}\), respectively, and surface roughness one order of magnitude higher than OA samples and smooth Al alloy reference (roughness like OA). IWT tests were performed following FAA specifications creating four different icing conditions (rime, mixed/rime, mixed/glaze, glaze) after each of them, ice adhesion strength was measured. Except for the glaze condition in which the adhesion strength remained unchanged for all surfaces (approx. 45 kPa), in the other three conditions, only the hydrophobic OA sample showed adhesion strength lower, 2-3 times, than the reference (Figure 7). This result was explained considering the different surface roughness between the samples supporting the theory that wettability alone is not synonymous with anti-ice. Another work supporting this theory is [11] in which the authors prepared, by different techniques (spin and spray coating) but the same mixture, two SHS with different surface roughness. Spin coated sample showed CA = 156\({}^{\circ}\), CAH = 5\({}^{\circ}\) and Ra = 500 nm, spray coated sample showed CA = 165\({}^{\circ}\), CAH = 4\({}^{\circ}\) and Ra = 8 \(\upmu\)m. After the IWT test (T = \(-\)10 \({}^{\circ}\)C, wind speed 10 m/s, different LWC conditions and size of microdroplets) it was observed that although the samples had similar wettability and CAH, different ice adhesion strength values were registered. The spray-coated sample showed higher values, similar to the reference, compared to the spin-coated one evidencing the dominant effect of roughness on icebrobleity.