## 2 Materials and Methods
### Materials  
Five different materials were used to evaluate the proposed procedure and to assess their efficiency in assisting a manual de-icing. The test materials were as follows:  
* Aerospace-grade 6061-Te aluminum As previously stated, the aluminum test plate served as the benchmark or reference. The surface finish as well as its wettability can thus be used to represent a painted rotorcraft surface. * Nusil This material consisted of a commercial silicone elastomer named Nusil. A hydrophobic surface results when applied to different substrates. The silicone polymerizes at room temperature to obtain a smooth surface finish. A primer was added to the surface prior to application to promote silicone adhesion. Since silicone is a viscous material prior to polymerization, it was applied using a simple brush. * SWIX LF5 This material consisted of a commercial Ski wax named SWIX LF5. This material is fragile when applied to a substrate and is generally used to enhance the performance of skiers in alpine ski. It is a fluoro-carbon-based wax, which is most effective in the temperature range of \(-8\)\({}^{\circ}\)C to \(-14\)\({}^{\circ}\)C. Fluorinated components have been shown to be efficient against water and ice adhesion. The application process consisted of heating the wax to 150 \({}^{\circ}\)C using an electric iron. Once melted, it was applied uniformly on the substrates which were at room temperature. * SurfEllent This material consisted of the commercial coating named SurfEllent. It is a commercially advanced anti-icing coating and is used for multiple applications. The material formulation is based on polydimethylsiloxane and acetoxy silane cross-linker. The coating was applied using a spray applicator. Figure 7: Partially melted and refrozen snow over aluminum reference plate of 30 cm by 50 cm. \(112\pm 1\)\({}^{\circ}\)and a contact angle hysteresis of 6 \(\pm\) 2\({}^{\circ}\). The SurfEllent silicone coating also had a contact angle in the same range with a value of 112 \(\pm\) 2\({}^{\circ}\) but with a slightly higher contact angle hysteresis of 10 \(\pm\) 1\({}^{\circ}\). Finally, material #5, i.e., the epoxy-based coating Wearlon, had a contact angle in the same range with a value of 110 \(\pm\) 3\({}^{\circ}\); however, its contact angle hysteresis was practically the same as that of aluminum with a value of 35 \(\pm\) 3\({}^{\circ}\). From these results, we can see that all of the materials' outer surfaces are in the same range with respect to contact angle and are more hydrophobic than that of the reference material, aluminum. The same comparisons can be made with the icephobic behavior characteristics as presented in Table 2.  
The two first characteristics are concerned with the ice adhesion measurement using two laboratory tests: the centrifuge adhesion test (CAT) and the push-off test (PO). These two methods are complimentary to each other since the CAT uses simulated atmospheric ice and is widely used and recognized by the industry. While PO, although it uses molded ice, better mimics the passage of a tool, and is therefore more representative of the targeted application presented here. The results presented for both aforementioned methods are illustrated as a function of bulk shear stress (\(\uptau\)) and also in terms of adhesion reduction factors (ARF). The first material, i.e., the reference aluminum, had an ice adhesion value in the same range for both methods with 609.5 \(\pm\) 36.8 KPA and 604.0 \(\pm\) 8.6 KPA for CAT and PO, respectively. This value of ice adhesion is in the typical range obtained for bare aluminum. The material showing the best results was Nusil with ARFs of 8.4 and 12.5 for the CAT and PO, respectively. It signifies that the ice adhesion was reduced by 88% to 97% depending on the method. The second-best ranked material was SurfEllent, with ARFs of 6.8 and 8.9 for the CAT and PO, respectively. SurfEllent, similarly to Nusil, is a silicone-based coating.