## 2 Materials and Methods
### Materials
Both showed a contact angle thay is clearly hydrophobic and a contact angle hysteresis below 10\({}^{\circ}\), which shows that they are unlikely to interact with water in its liquid state or adhere with water in its solid state. The second element to consider was their uniformity and smoothness. Both offered a complete smooth coating of the surface and did not show visual anchoring points for ice adhesion. The third-best ranked material was the Swix wax with an ARF of 2.2 with the CAT and an ARF of 10.7 with the PO. The results were much better with the PO than the CAT. This can be attributed to the type of ice used during the tests. Since the waxy material is not designed to adhere perfectly to a metal surface, the coating may not be completely uniform. So, when small droplets like freezing drizzle are deposited on the materials surface, some of these droplets will remain on the top of the wax; however, some may penetrate further to the substrates surface and can thus partially anchor themselves with the aluminum. This phenomenon is less pronounced with the PO test because the ice is formed by molding a fixed quantity of water that does not penetrate the wax prior to freezing. The same reasoning can be drawn with the contact angle since the water drop of 5 \(\upmu\)L remains on the top and does not penetrate. Finally, the last performant material, in terms of low ice adhesion, was the epoxy base Wearlon. Although the result in the CAT provided an ARF of 6.0, the ARF in the PO test was only 1.1. In this particular case, we can correlate it with the value of the contact angle hysteresis, which is practically the same as that of aluminum, and thus the presence of anchoring points promotes ice adhesion. Visual inspection of the Wearlon also confirmed the presence of millimetric anchoring points that may increase ice adhesion. Materials may react differently depending on the icing conditions used. Therefore, ice adhesion \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material \#** & **1: Reference** & **2: Nusil** & **3: Swix** & **4: SurfEllent** & **5: Wearlon** \\ \hline \(\uptau\) CAT (KPa) & 609.5 \(\pm\) 36.8 & 72.5 \(\pm\) 4.1 & 319.0 \(\pm\) 70 & 89.2 \(\pm\) 1.9 & 101.5 \(\pm\) 9.1 \\ ARF CAT & - & 8.4 & 2.2 & 6.8 & 6.0 \\ \(\uptau\) PO (KPa) & 604.0 \(\pm\) 8.6 & 48.5 \(\pm\) 8.5 & 56.4 \(\pm\) 9.7 & 67.9 \(\pm\) 4.1 & 527.0 \(\pm\) 5.6 \\ ARF PO & - & 12.5 & 10.7 & 8.9 & 1.1 \\ Freezing delay (sec) & 126 & 1982 & 1045 & 828 & 336 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Icephobic assessment. measurements illustrate the importance of using multiple methods prior to establishing a material as icephobic. To deepen the understanding of icephobic material behavior for aircraft application, it is necessary to thoroughly analyze the mechanism of ice formation (the process of nucleation and growth). The fundamental and crucial step for the formation of ice is known as nucleation. Freezing of a small quantity of water (e.g., a droplet) does not occur immediately after contact with a cold sub-zero surface. Prior to nucleation, the time required for a droplet of water to freeze, once in a supercooled state, is called the induction period. This induction period if often referred to as the \"freezing time delay.\" In this project, the longer the freezing delay, the better the material. The freezing time delay is defined as the time interval between the impacting of the water droplet on the pre-cooled substrate and the onset of freezing. Preliminary data on the freezing delay of the water droplet for the reference material surface, aluminum, were determined to be 126 s. Overall, the initial results showed that the maximum freezing delay of 1982 s was achieved with the Nusil surface, which was more than 15 times that of the reference aluminum. In other words, the formation of ice can be effectively delayed by the Nusil surface at a temperature and humidity of \(-10\)\({}^{\circ}\)C and 20%, respectively.