# Superhydrophobic Coating Solutions for Deicing Control in Aircraft
## 3 Superhydrophobic Surface with Icephobic Behaviour for Aircraft Applications  
### SHS Not Tested in Flight Conditions  
In the literature, some papers aimed to explore the application of superhydrophobic coating in aeronautical fields conducting resistance and anti-icing tests in non-standard conditions. These works could be considered as preliminary and some of them, are indeed a first step of works that applied more stringent and adherence tests to what are the real conditions of use.  
[PERSON] et al. presented two works [25; 26] in which an SH coating was characterized on a lab scale. The SHS, in both papers, was prepared following the procedure in [27] and the SH coating was applied on different aeronautical substrates, in terms of material and roughness, and the icophobicity was tested by observing the shape of water-frozen droplets (\(-27\)\({}^{\circ}\)C) (Figure 5) and then the surface wettability. Cutting and tape tests according to ASTM procedure were performed to evaluate mechanical abrasion resistance. Furthermore, the work of adhesion and surface free energy of the prepared surface was calculated and correlated with sample surface roughness. The authors observed that the SH treatment was necessary to reach high CA and the roughness, regardless of the material, decreased after surface modification, and different roughness can allow the same CA. The works conclude by stating that prepared surfaces can reduce the contact area between ice and substate and that adhesion work, obtained from surface free energy value, was reduced by more than 80%.  
Figure 4: Successive snapshots of ice melting process for adhesion test, the original Ti mesh is on the left and the SSTM is on the right. Reprinted from Applied Surface Science, 476, [PERSON], [PERSON], [PERSON], [PERSON], Preparation of superhydrophobic/superoleophilic copper coated titanium mesh with excellent ice-phobic and water-oil separation performance, 353–362, Copyright (2019), with permission from Elsevier [23].  
[PERSON] et al. [28] developed and tested different PDMS-based icephobic coatings for aircraft applications. In this study PDMS coating was fluorinated (F/PDMS) to increase the wettability (CA = 124\({}^{\circ}\)) and, to enhance the CA up to 157\({}^{\circ}\), fumed silica was added (F-PDMS/silica). An initial test used to study icephobicity was to deposit a water drop on a surface at a temperature of \(-10\)\({}^{\circ}\)C, from this test it was observed that the greater the CA, the smaller the contact area between ice and surface. On the other hand, a lower value was observed for the hydrophobic sample. This result was justified by the different roughness between the samples, SH F-PDMS/silica surface showed an average surface roughness of 7.3 \(\upmu\)m while hydrophobic F-PDMS 1.6 \(\upmu\)m, with high values meaning high interlocking of the ice within the surface. To investigate operating conditions similar to those of a future application, wettability measurements were performed at a pressure of 0.5 bar and temperature of \(-12\)\({}^{\circ}\)C. In such conditions, the CA of the SHS decreases to 104\({}^{\circ}\) (reduction of air pockets). From these works, it can be observed that, although the purpose of use of the investigated surfaces is for aeronautical applications, the conducted tests do not follow standard specifications and are rather subjective. Comparing these works, it is also observed that surface roughness at macroscopic magnitudes is important to define ice adhesion but is not sufficient to define a surface as icephobic.