# Superhydrophobic Coating Solutions for Deicing Control in Aircraft
## 2 Superhydrophobic Surface with Icephobic Behaviour for General Purpose  
In recent years, the research on the prevention of ice and frost has significantly grown since this problem affects numerous fields. Superhydrophobic surfaces, due to their low water wettability, are regarded as the most promising materials with anti-icing properties. As we shall see, this statement is partly erroneous because much depends on the actual conditions under which the coating will be exercised (aerospace, marine environment, energy systems). Much research that tries to find a solution to this problem provides results that need to be investigated through specific tests for the different industrial applications. [PERSON] et al. [22] prepared a macroscopic Al honeycomb structure by electrospray on an SHS with high mechanical strength and anti-icing behaviors. The coating on the honeycomb structure has CA = 161.1 and roll of angle (RoA) = 5.6\({}^{\circ}\). The particular honeycomb structure combined with the low wettability can explain the results from the icing test, in fact, it was observed that at different temperatures below 0 \({}^{\circ}\)C the complete freezing time increased for SHS and was better for the honeycomb structure. Also, the frost formation on the sample surface tilted at 60\({}^{\circ}\) and at T = \(-\)20 \({}^{\circ}\)C was less on the SH honeycomb surface both compared to the sample taken as a reference and especially compared to the superhydrophobic on a smooth surface. Another example is the work of [PERSON] et al. [23] in which the authors affirm preparing an SHS with icephobic behavior. The titanium SHS was prepared via chemical immersion in copper solution and a successively annealing after that the surface showed a CA of about 158\({}^{\circ}\). Icephobicity was tested just by observing the behavior of the water droplet on SH and reference surfaces cooled at \(-\)16 \({}^{\circ}\)C or observing ice melting on the two surfaces. The authors observed that on SHS, water needs more time to freeze compared to reference and ice, once melted, formed a spherical water droplet able to roll off the surface (Figure 4). [PERSON] et al. [24] reported the creation of a superhydrophobic surface with ultra-low ice adhesion without a specific application. For this reason, in this paper, the anti-icing tests did not follow standard protocol. The authors prepared an SHS based on a sprayed PDMS microsphere and OTS@SiO\({}_{2}\) np (OTS is octadecyl trichloro silane), on fluorocarbon resin (PDMS/SiO\({}_{2}\) based surface). SHS show CA = 171\({}^{\circ}\) and Sa = 0.277 \(\upmu\)m. The Sa was ten times lower with respect to the PDMS coating and in the same order of magnitude coating with only OTS@SiO\({}_{2}\). From static and dynamic anti-icing tests with the surface at \(-\)10 \({}^{\circ}\)C, it was observed that the PDMS/SiO\({}_{2}\)-based surface had good anti-icing ability as it was able to prolong the freezing time probably due to a greater CAH (not reported). Ice adhesion was further evaluated by freezing an ice block on the different surfaces and measuring the shear force to detach ice. The test produced a result in line with previous observations confirming  
Figure 3: From synthesis to tests, a passive icephobic solution design path to hybrid systems. Reprinted from Progress in Aerospace Sciences, 105, [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON], A survey of icephobic coatings and their potential use in a hybrid coating/active ice protection system for aerospace applications, 74–97, Copyright (2019), with permission from Elsevier [21]. the anti-ice behavior of the prepared SHS. Also, the surface maintains its wettability after 100 mechanical abrasion cycles. These are just a few examples where we can see how surfaces are deemed icophobic but in a general context. In addition, the used tests to assess it are nonspecific and, in some cases, exclusively qualitative rather than quantitative.