# Superhydrophobic Coating Solutions for Deicing Control in Aircraft
## 3 Superhydrophobic Surface with Icephobic Behaviour for Aircraft Applications
### Hydrophobic and SLIP Surfaces with Icephobic Purpose Tested in Flight Complaysditions  
It was observed from the literature that it is difficult to obtain SH surfaces with anti-ice behavior and durability; some authors directed their research toward other types of surfaces. [PERSON] et al. [38] in the present study proposed three hydrophobic coatings, prepared by different techniques and materials, with anti-icing behavior to deepen the use of coatings for passive solutions in airplanes. The three coatings were tested in IWT (air speed 50 m/s, T = \(-8\)\({}^{\circ}\)C, LWC 0.36 g/cm\({}^{3}\)) evaluating ice accretion and durability after some icing-deicing cycles. From these tests, it was observed, considering also reference material such as PTFE and Al substrate, that the anti-icing behavior was a combination of surface roughness and surface energy. Materials with similar roughness (coating 1 and PTFE) showed different ice adhesion and high roughness was more important with respect to low wettability. The best coating was that showing CA = 88\({}^{\circ}\) and Ra 0.19 \(\upmu\)m but the results are far from a possible aeronautical application due to its low mechanical resistance. SLIPS are a category of materials recently investigated for applications in aeronautical applications. [PERSON] et al. [39] prepared and tested them in IWT to evaluate the ice accretion in rime and glaze conditions. Two different SLIPS were prepared, one was Al\({}_{2}\)O\({}_{3}\)-based and the other was SiO\({}_{2}\)-based and both were infused in perfluoropolyether lubricant oils (two liquids that differ in terms of viscosity). IWT were conducted in different conditions but same velocity, 50 m/s, to obtain glaze and rime regimes. Al\({}_{2}\)O\({}_{3}\)-based and SiO\({}_{2}\)-based SLIPS showed similar CA around 120\({}^{\circ}\) depending on the used lubricant oil and not on the substrate material. An important difference was the morphology of the samples: Al\({}_{2}\)O\({}_{3}\)-based coatings showed a flower-like structure, and SiO\({}_{2}\)-based showed nanoparticles agglomerate with larger pores compared to alumina coatings. Both SLIPS displayed a decrease in ice accretion with respect to the uncoated surface, in particular, silica-based showed a reduction of up to 45% in glaze conditions. In rime, ice conditions not much improvement was observed compared with the reference. Also, [PERSON] et al. [40] studied SLIPS as an anti-icing solution comparing them with self-prepared SHS. Both surfaces were formed by PVDF deposited by electrospinning technique and silicon oil was used as liquid to fill the porous PVDF structure and obtain the SLIPS. The prepared SH surfaces showed a linear correlation between CA and Sa, the highest value of CA (about 162\({}^{\circ}\)) was reached for the roughest sample (Sa = 700 nm). The SLIPS obviously showed low CA (106\({}^{\circ}\)) but the value of CAH (SHS CAH = 30\({}^{\circ}\), SLIPS CAH = 19\({}^{\circ}\)) denoted how droplet mobility was better on this surface. Anti-icing behavior, on the best SHS and on SPLIPS, was tested in two conditions in IWT (air speed 70 m/s, T = \(-5/-15\)\({}^{\circ}\)C, LWC 0.5 g/cm\({}^{3}\)) in order to produce glaze and rime ice, and adhesion test was performed using a centrifuge. PTFE and Al were used as a reference and in both glaze and rime conditions, as shown in Figure 8, SHS showed higher ice adhesion (especially in glaze conditions) than PTFE, while SLIPS achieved low ice adhesion in both conditions (four and seven times less of PTFE). SHS sample lost its property after only one cycle of icing/deicing instead of SLIPS that resisted up to four cycles. The surface was still not resistant considering that AI and PTFE did not show degradation after the test. From these studies, it is possible to observe that SLIP surfaces are more performant compared to SHS due to the presence of lubricant in the microstructure that avoids water penetration and ice interlocking with the surface.