# Parameter Study for the Ice Adhesion Centrifuge Test
## 3 Results
### Interdependencies of the Surface Properties and Ice Adhesion Strength  
The effects of the surface properties on results of the ice adhesion centrifuge test are assessed in the following section. Figure 8 shows exemplarily R\({}_{\text{a}}\) values (arithmetical mean deviation of the assessed surface profile) as an often-used basic parameter for the surface roughness in comparison with the ice adhesion strength per ice formation type.  
The PUR C25 material with the lowest material roughness in this study showed the lowest ice adhesion values in all ice formation types. For impact ice, accreted at 95 m/s (dotted line), the increase in the ice adhesion strength correlated with an increase in the roughness for the materials Standox (R\({}_{\text{a}}\) = 0.07 \(\upmu\)m) and PTFE-tape (R\({}_{\text{a}}\) = 0.11 \(\upmu\)m). This changed for ice accreted at lower velocities and for static ice. The measured ice adhesion strength was comparable (60 and 40 m/s velocity) or higher (static ice) for the smoother Standox material than for the PTFE-tape.  
These findings may be explained by the underlying ice formation processes. Impacting water droplets (velocity 95 m/s) may enter the surface structure of PTFE-tape. They can  
Figure 8: Surface parameter R\({}_{\text{a}}\) and ice adhesion strength data for different ice formation types.  
Figure 7: Comparison of the ice adhesion test results at different centrifuge acceleration speeds.  
overcome the low material wettability (SFE = 15.1 mN/m) due to their high energy, resulting in a higher ice adhesion than for water with less or zero impact energy. This is also of specific relevance for superhydrophobic surfaces (high surface roughness, low wettability), which were not included in this test program due to their expected limited durability.  
It is further postulated that with a significant increase in the roughness (as for the primer R\({}_{a}\) = 1.5 \(\upmu\)m), the ice adhesion strength increases significantly, regardless of the ice formation type. The surface wettability, as the second main surface property, is displayed in Figure 9 against the ice adhesion test results for different ice types. The surface free energy (SFE) was selected as the parameter for this evaluation.  
The lowest SFE of the PTFE-tape (SFE = 15.1 mN/m) in this study did not result in the lowest ice adhesion strength (as presented before). PUR C25 (SFE = 18.0 mN/m) showed lower ice adhesion test results for all ice formation types. The effects of the ice formation types and the interdependencies with the surface properties roughness and wettability included the following:  
* For high impact velocities (95 m/s), the surface roughness is of higher relevance than the wettability properties, resulting in increased ice adhesion for the rougher but low-wettability PTFE-tape compared to the Standox coating.
* For lower impact velocities (60 and 40 m/s), the roughness and wettability properties cancel each other out, resulting in comparable ice adhesion results for the PTFE-tape and Standox material.
* For zero impact velocities (static ice), the surface wettability is of higher relevance than the roughness, resulting in a higher ice adhesion strength for Standox compared to PTFE-tape.  
These findings are of significant importance for the development of icephobic materials and the definition of accompanying test designs. As soon as surface structures (used to reduce the wettability by increasing the roughness) are addressed, impact ice formations need to be considered to minimize the risk of overestimating the reduction in ice adhesion under relevant technical conditions. Therefore, the definition of test parameters should also address the desired technical applications.